Florescent and LED spectrum is nowhere near flat
 

I've been researching light spectrums for LEDs, florescents, and tungsten lights. I'm aghast at how non-flat the spectrum is for even the best of the LEDs and florescents. Even the best of class (Litepanels and Kino) are nowhere near as smooth as tungsten light when you look at the graphs.

In the case of flourescent there are huge spikes in the blue and green, and good LEDs have broad peaks in blue and then a dip, then another broad peak up towards red. Non best of class can have all kinds of nonlinearities in addition.

This echoes my experience, that I can get white to be daylight white fairly easily with tungsten or strobes, but with my medium-grade LEDs and florescents I'm going to need to do quite a bit of experimenting to find just the right gel to match daylight.

For those of you who successfully use LEDs or florescents, I am curious, are you able to mix them with daylight and still get whites, or do you custom-balance at camera or in post to get them white? And do you find that once balanced they give just as good color rendering as tungsten?

In other words, even if you get the RGB balance spot on, is it even possible to get really great color with spikey or peak/valley spectrums like these? I would think that if something in your scent happened to reflect the same wavelength as a flourescent spectrum it would glow unnaturally bright. The one thing I can't figure out from the graphs I see is how much energy is in those spikes... I know they are really high, but just how wide and how much area is underneath them? That is hard to evaluate.

It would seem that because LEDs generally don't have those huge florescent spikes, they should give better CRI once RGB balanced. But then why do LEDs seem to always be said to have lower CRIs than florescents by those tho know? Is it just the RGB balance that needs correction on the good LEDs or is there something I'm missing?

After buying and testing a few LED and florescent lights I'm considering selling them and going to tungsten because this problem is more intractable than I had imagined. I know part of the issue is that I'm not willing to spend for the best (Kino and Litepanels), but is this industry still so immature that medium grade stuff just can't be mixed with real daylight to critical standards?

I'm using ephotoinc LED 1200's, a Flo-light FB2500, and an assortment of 45w, 65w, and 85w CFLs.

Re: Florescent and LED spectrum is nowhere near flat
 

Tom,

The major driving force behind both fluorescent AND LED lighting is not color spectrum. It's energy efficiency. And there are TWO very important elements to that.

In the field, the VASTLY superior energy efficiency yeilds significant cost savings in powering them - whether on location or on a set. In fact, LEDs are so energy efficient, that area lighting via simple lightweight battery powered units is finally possible.

In the studio not ONLY do you get direct energy savings by virtue of the minor power draw, but UNLIKE tungsten units, the vast majority of the energy in BOTH of these technologies goes into producing light - rather than HEAT - a factor that eats up MORE energy and drives up direct costs when it comes to studio HVAC.

Yes, there are spectrum issues. However, the judicious use of filtering (subtractive magenta for counteracting some of the green) - and more important, the ability of modern editing suite software to "re-color balance" in post - makes it perfectly possible to generate very good on-screen results with these amazingly efficient light sources.

If perfect color balance or absolute color reproduction is your holy grail - you may never be satisfied with these light technologies. If lights that do a decent job, sip rather than gulp power, and are much, MUCH, easier to pack and travel with than any tungsten kit on the planet are more important to your practice, than there's a place for all of these.

As in all lighting - horses for courses.

Re: Florescent and LED spectrum is nowhere near flat
 

Yes, I am closing in on getting the color balance back to white with gels and perhaps some tweaking in post. But this hassle is nontrivial. And yes these are amazing energy savings.

But I rarely hear people talk about the way that skin tone looks more sickly, and green casts can still come about.

The spectrums can be seen overlaid on each other by going to this page:

Solid State Lighting Project | Science & Technology Council | Academy of Motion Picture Arts & Sciences

Then starting the "Summary" video under "Symposium videos" on the middle right of the page, and going to 1:37 in that video.

You can see that LED and Florescent have much different slopes and peaks than the film responses (designed to match human vision) which video tries to emulate.

The case study videos underneath also demonstrate the sickly skin tones that can come about, especially with lighting source number three, which is probably florescent.

Re: Florescent and LED spectrum is nowhere near flat
 

Looking at charts and graphs drives me crazy. I can't stop focusing on stuff like green spikes.

The same thing happened to me when I was looking at the 5DMkII when it first came out. How can anyone shoot with a camera with so much judder? I looked at youtube videos by the dozen where the photog was zoomed in on a brick wall and would swish pan back and forth - the lines between the bricks were so curved that you couldn't tell it was a brick wall anymore!

I ended up buying the camera anyhow - I've never replicated the problem in real life. Turns out I don't do a lot of swish panning in front of brick walls.

I was totally worried about the green spike when I moved to Kino Flo, I used to gel everything with 1/4 minus green. One day left that roll back at the shop. Thought we'd have to cancel the shoot. Decided to shoot it anyway just to see. Could hardly tell the difference.

Didn't even worry about gelling the LEDs. Love the flexibility to run them off 12V or in an office without a generator mucking everything up. The best move I've ever made.

One man's opinion.

Re: Florescent and LED spectrum is nowhere near flat
 

technically fluorescent AND LED lighting are the same technology, so you can expect the same behavior.
What you get is is the light emitted by some layer of phosphor activated by some IR or UV light.
you can expect the led to be better only if you mix several leds with different spectrum (intentionally or being lucky).
for my home made led lightsm i use a mix of warm white (yellowish) and white (blueish) so the average is better than only one type of led.

Re: Florescent and LED spectrum is nowhere near flat
 

Just FYI, even real daylight doesn't have a "flat" spectral content graph.

The best lighting tools get close, but not precise. Knowing where the deficiencies are, and your purpose, can help you make the best decision.

Re: Florescent and LED spectrum is nowhere near flat
 

Just out of curiosity, where are you getting your spectrum graphs? I wish it was standard procedure for manufacturers, like including lumen rating and estimated bulb life.

Re: Florescent and LED spectrum is nowhere near flat
 

I have a spectrometer that will create a graph of a light's spectral distribution.

I'm able to compare different light sources and see where they might be excessive or deficient in terms of wavelengths. It makes it a little easier to find the right filters sometimes.

My LED work-in-progress experience (long)
 

Tom, if it's any consolation, I've been going through the same problem you are. As for background, I'm what one would call a hobbyist or amateur and got really bitten by the video bug last summer when I was given a free video camera. Since then in order to improve my videos I've acquired literally hundreds of dollars of equipment and the more I get into this the worse things are looking, and sounding (there's audio too). The past couple weeks has been my lighting nightmare from hell which is basically the same thing you're dealing with.

Here in the Great Northwest we're experiencing winter - you know, rain, rain, and more rain. And, it's cold and windy outside. This will continue basically until August when I can finally get outdoors and capture the video I've been dreaming about. But for the time being I decided to use my video lighting (three Cool Lights CL-600LED Floods) to take still pictures of stuff in the house in order to de-clutter the place. Now the problem starts: The pictures were too green. I tried editing in iPhoto but getting the right color temperature, tint, contrast, saturation, and exposure is, shall we say, a royal pain.

Plan A: I found that by using the camera flash I could mostly drown out the green but this caused other problems such as reflections from the subjects (items intended for sale on crags list and eBay).

Plan B: I found a Lowel L-light fixture for sale on crags list and since they were close by and it was cheap so I bought it with the intent of flooding the scene (dining room table with my items on a foam white board) using a fluorescent EiKO 5500K "daylight" bulb which is supposed to be one of the best (I was told). Well, this didn't work either because the pictures actually came out more green! It may be that the fluorescent bulb needed to be on longer to warm up more but I didn't test this aspect.

Research: A call to Lowel about what bulb they would recommend led me to their technical person who was a lot of help with explaining my problem but didn't have a particular bulb recommendation. The next call was to EiKO and I talked to Rick Porter, National Sales Manager for North America Photographic Bulbs. This was very enlightening and while I've been a little long-winded here, what I learned would easily double or triple what I've written. In summary, bottom line, for me the best solution would be to go with tungsten. Why? because (1) it is very consistent in the 2600K to 2650K range, (2) it is a known science, and (3) it has repeatable results.

Depression: So here I sit with three LED "daylight" light fixtures. What to do? Switch to Tungsten?

Masochist: Naaaa….. let's try one more thing. While the current pictures are for crags list and don't need to be that perfect, this IS laying the groundwork for my future videos.

Plan C: I didn't get any filter packs with the lights so that option was out until I had digested all this new information. Rather than switch to a new system I decided to order filter packs. They came yesterday and within 30 minutes I had run test pictures using no filter, 1/4-minus green, and 1/2-minus green. The results showed that the filters really helped but I'm not very satisfied because the 1/4-minus looks a little green and the 1/2-minus looks a little pink. Maybe that's because of my computer screen or the light I'm viewing the computer screen in, but that was yesterday. This morning the 1/2-minus seemed to look better.

Continuing Problem: The green spikes are clearly visible during the color editing process and I'm not very adept at removing them. One can increase or decrease certain things like the OVERALL color temperature, tint, etc. but, at least in iPhoto, not INDIVIDUAL, and especially multiple individual, areas of the color spectrum, and it's not good with dealing with spikes. Maybe a different and more expensive program ("modern editing suite") will but that's not on my option list. If I'm having this much trouble with still life I can only imagine what it's going to be like with video.

Plan D: Go to DVinfo.net and read what others have to say.

Bill Davis, Post #2, said it well. The LEDs have their advantages but a table-top "studio" (aka "wife's dining room table") in the hands of a novice is probably not one of them. Mixing light types someone said is not a good idea either. What Bill said about HVAC loads is not a problem here, well, at least not he AC part.

I can identify with Mike Watson, Post #4, about the green spikes driving one crazy - I can identify with that.

Currently I'm monitoring the local craigs list ads for some tungsten lights with soft boxes but in the meantime progress is continuing with my "close enough" product shots of "stuff" for selling but I'm very concerned about the next step which will be my dream video effort.

I want: a spectrometer like Dean has!

Re: Florescent and LED spectrum is nowhere near flat
 

I'd love to have a high-tech spectrometer too....but there is a free alternative I found here:
A CD spectrometer

Re: Florescent and LED spectrum is nowhere near flat
 

I guess I'm just a little old fashion, as I have been gelling lights for over 30 years and have never thought that getting the right look was a nontrivial hassle. Unless you are a hobbyist it's part of the job.

With using fluorescent or LED lights, I simply use my old trusty Minolta Color meter II to quickly determine the appropriate gels needed to bring the lighting instrument into spec. It may be a 1/8 minus green along with a 1/4 CTO for example. For what it's worth... I own a variety of different lighting instruments, and have found that LED and Flo lights can be used to great effect once you learn how to balance them.

Good Luck!

Dave

Re: Florescent and LED spectrum is nowhere near flat
 

I can't tell you what the technical difference is between high and low end flos and LED's, but the bottom line is that the products packaged for the film industry photograph just fine. Most features and TV shows utilize both technologies and the skin tones are obviously acceptable there.

I use LED's from companies like Litepanels, Zylight and Litegear--the last being a fantastic system developed by an IA gaffer based around color corrected LED's which is a great problem solver for tight spaces. Just like the other manufacturers, these LED's are a lot more expensive than the similar looking variants but are suitable for lighting talent. I haven't seen information on whether or not they present spikes under a spectrograph, but all I know is that they look good in the final product, which is all that counts to me.

Re: Florescent and LED spectrum is nowhere near flat
 

I've kind of got used to all this over the years because I do theatre work where the main sources illumination is tungsten halogen at 3200ish, however theatre lighting tends to run at almost any point on the dimmer scale, rather than the TV method of a bit over and a bit under .7 on the dimmer - which is a manageable colour shift. The trouble for me is that we also now have lots of discharge sources at 6000ish and it's always difficult to know what to colour balance to. My usual method depends on if the show has follow spots, and white balance on their colour temp - this leaves everything else with a predominant red cast - but now we add in led lighting and it's yet another weird colour - the spikes aren't really a big problem, but they mean that it's almost as if they have a bit of gel on them. For us theatre types we can cure this fairly easily, because our LED fixtures are usually RGB (or even RGBA) so we can adjust the 'white'. We do now have some white LED theatrical fresnels, but these are a nuisance to try to return back to white. In most cases, the shift isn't too noticeable - especially if they're bright because they tend to squash the whites anyway when they are used in multiples.

The only time I see problems is with mixed face light.

BINGO! (1/4-minus *plus* 1/8-minus)
 

Oren (Post #10): That was a great link to the CD spectrometer. Talk about a low budget setup and this has to be it. The examples were very interesting and example (12a), the Moon where he used a telescope was a good one because it shows that the light can be manipulated/concentrated and the spectrometer can still work.

By the way, tonight, March 19, 2011 (or maybe tomorrow night?) the moon will appear it's largest for over a decade. Details should be googleable.

Speaking of Internet research, I looked up David Jones' Minolta Color Meter ii (or II) and found a number of hits, including one at Minolta Color Meter II Review where he tells how his II is making a comeback. Used ones on eBay run in the $300 to $400 range and the III in the $700 to $800 range. Now that's getting up to what I paid for all my lighting!

Another item of interest is the daylight color setting that is designed into the camera. While talking to Rick Porter (see post #9) I learned that camera manufacturers use different daylight norms in the design of their cameras, and even within various models of the same manufacturer. Then add the computer program that is used to view the digital data and the computer itself, and now you have a real assortment of how a picture can be viewed, and this is assuming someone doesn't have eye issues.

Also, David Jones (#11) said he might use a 1/8-minus along with the 1/4-minus and based on my test results I think that will be my solution too.

Re: Florescent and LED spectrum is nowhere near flat
 

Great points all around with regard to the absolute accuracy of lighting, but it's missing the point. With more efficient lighting, the scene/room/studio stays a cooler temperature (and I'm not talking color temperature). That means my talent doesn't sweat as much and I don't need to slow production to do touchups every other take.

And less chance of a fire or injury means lower liability exposure, cheaper insurance, etc. A slight shift in color won't get noticed by 99.999% of the audience and if the performances are better as a result, then the product has improved.

I'm not crazy about LED/fluoro lighting from an optical standpoint but it makes up in other areas.

Re: Florescent and LED spectrum is nowhere near flat
 

I'm with Jad. I hate walking into a new room and praying that I can use more than 3 tungsten lights at a time without:
A) cooking the talent
B) blowing a fuse
C) frying a bulb
D) melting the fake Ficus tree

Tungsten has had a great run. Three cheers for Thomas Edison. My future lighting budget will probably not spent on hot filament technology.

Re: Florescent and LED spectrum is nowhere near flat
 

I was shooting our cooking segments in a room that had lots of cool daylight but needed additional lighting to provide some directional qualities.

The supplemental lighting was from two CoolLights 600s, fitted with "minus 1/2 green" filters, plus one small Kinoflo that I got via Craigslist for $65.

I put a tungsten "hair light" in the back to provide some additional warmth to the stainless steel environment.

There has never been a problem with a green spike. And the food comes out looking good.

Attached is a frame grab from the Sony EX1.

http://hawaiigoesfishing.com/images/...ok_&_print.jpg

Re: Florescent and LED spectrum is nowhere near flat
 

Hey, that CD spectrometer was a fun little project. I'm not getting anywhere as nice results as the web, but I do feel like I'm getting a sense of the spectrum of my lights with it.

I've been watching video more carefully since this discussion, and often noticing sickly color casts in some of the newer TV shows that might be using flourescent lighting (House, 24). I'm guessing this is one of those "you'll get used to it" things, kinda like CD sound in the 1980's.

I did some experiments and determined that 1/8 minusgreen on the LEDs and CFLs, and 1/4 minusgreen on the 5000k linear tubes looks like it will come closest to neutral. Next task is to try them out and see how close we came.

I've always liked incandescent light, and now I really know why... there's just more information there.

Re: Florescent and LED spectrum is nowhere near flat
 

Hmmmm...probably not. Kino's have been in use now for 25 years. You've seen plenty of movies and TV shows shot with them without "sickly" color casts. That particular look is deliberate and often dialed in in post as a choice. If there is a difference between corrected fluorescent and tungsten light, it's pretty subtle. I've always meant to shoot a head to head comparison, might still be an interesting procedure and maybe include a quality LCD unit as well.

Re: Florescent and LED spectrum is nowhere near flat
 

You know, that's the one thing I haven't seen on the kino site is a side by side flor vs tungsten photo to show how well they can render light. If anyone has good examples I'd like to see. Obviously it's not trivial getting the light shaped the same from different bulb sizes, but a really accurate test could be done illuminating a frosted window indirectly to illuminate a scene.

Re: Florescent and LED spectrum is nowhere near flat
 

It would be fairly easy to duplicate the effect of a Diva 400 or a 2 ft 4 bank with diffusion over it by using a tungsten unit and shooting it through the same size diffusion (to minimize variables). The color temperature may shift as a result but at least it will be the same shift in both. Don't know if I'll ever get around to it but it would be an interesting experiment, especially to put the images up here as a blind test.

Re: Florescent and LED spectrum is nowhere near flat
 

Tests recently performed by The Academy of Motion Picture Arts and Sciences (AMPAS) has revealed a lot of the information in this thread to be untrue. The AMPAS tests clearly demonstrate that all LED panels that use Phospher White LEDs (Litepanels, Cool Lights, etc.) are so deficit in certain parts of the color spectrum that they are inherently incapable of rendering colors accurately and so don’t mix well with other light sources. It also reveals that the high CRI claims of LED manufacturers to be nothing more than the “emperor’s new clothes”.

If you look at the Spectral Power Distribution graphs of Phosphor White LEDs (available at ScreenLight & Grip's E-Newsletter) you see that, as Tom noted at the outset, they have a discontinuous spectral quality that is unlike that of natural daylight, HMI, or incandescent light. In the case of the 3200K Phosphor White LEDs, the phosphors added shape the spectral distribution by enhancing certain colors in the spectrum to simulate the spectral distribution of incandescent light. As a result, the spectral distribution of Phosphor White LEDs resembles a series of peaks and valleys with a big spike at about 465nm (the blue “pump” LED) and a broader bump between 500 and 700nm produced by the phosphors. While the discontinuous spectral distribution of high CRI White Phosphor LEDS may appear white to the eye, and the color of objects illuminated by it appear natural to the eye (hence their high CRI), to film emulsions and digital imaging systems designed to reproduce accurate color under continuous spectrum light sources (like daylight or incandescent lamps), the color of the same objects appear slightly off on screen. For example, in a company newsletter on this subject, I have posted a split Macbeth chart showing the visible effects of studio tungsten light in the top half of each color patch, and a high CRI White LED (that shall remain nameless) in the bottom half.
It doesn’t take a calibrated reference monitor to see the wide variations in color patch hue caused by the discontinuous spectral distribution of the Phosphor White LED.

What accounts for these results? Phosphor White LEDS, compared to continuous light sources, have no output at wavelengths shorter than about 425nm, which means that violet colors don't render well. Second, there is minimal output in the medium blue-cyan-turquoise range from about 465-510nm, which is why the aqua-type colors don't render well either. Third, with the long-wavelengths cutoff in the high-600 nm range, pinks, reds, oranges, and other long wave-length colors tend to look a little dull under Phosphor White LEDs, compared with how they look under a continuous spectrum light source like Tungsten which extends all the way out on the long-wavelength end. Lacking these colors within the spectrum, skin tones also look pale under Phosphor White LEDs.

For side-by-side comparisons between Phosphor White LED fixtures and Tungsten see a newsletter article I wrote on this subject that is available at ScreenLight & Grip's E-Newsletter.

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

Good luck trying to correct all the deficiencies of LED panels noted above with gels. Even the better LED light panels, like the Litepanel 1x1s (forget about the Cool Lights LEDs), are so deficit in certain parts of the color spectrum that by the time you came up with a color gel pack to match them to a continuous light source like a tungsten or HMI light, the LED panel would put out very little light with all those gels on it.

While you can white balance out/time out the characteristic green/magenta bias of Phosphor White LEDs in digital video cameras/digital film intermediate, the camera/timer is not able to replace the parts of the spectrum that are missing all together. And since gels only rebalance the spectral distribution of a light source by passing the wavelength of the color that they are, gels cannot correct for these deficiencies either because there is not light of those wavelengths to pass in White Phosphor LEDs to begin with.

This inability of Phosphor White LEDs to render color is very visible in the tests Tom mentioned that The Academy of Motion Picture Arts and Sciences (AMPAS) recently performed. In one a model was photographed wearing a dress that had a number of different blue/cyan tints. Footage was shot with both a tungsten source and a Phosphor White LED source (see ScreenLight & Grip's E-Newsletter for the results.). The tungsten-lit footage displayed all of the subtle differences in blue/cyan tones in the fabric, while the LED-lit footage, lacking cyan output, showed just a nice blue dress, without the same richness of hue. Since the light doesn’t put out much cyan, the camera/film simply can’t record it. You can also see in the side-by-side comparison that, the skin tones of the model don’t stand out because of the rapid drop off of long wavelength colors within the spectrum of White Phosphor LEDS. The bottom line is that, simply by nature of their discontinuous spectral distribution, all high CRI Phosphor White LEDs (Cool Lights and Litepanels included) will never accurately reproduce colors on screen regardless of how much gelling or post production correction you do.

While they are less than perfect at reproducing parts of the color spectrum, the color rendering of Phosphor White LEDs may, as Bill points out, be adequate in certain situations. For a specific application, say where lights must be operated off of batteries, a LED fixture offers the unique advantage of greater power efficiency over conventional lights, which may out weigh its shortcomings in color rendering. However, a Phosphor White LED is clearly not the best choice in applications where color rendition is critical (food/product shots) or mixed with a uniform continuous light source, such as a studio lit with tungsten fixtures, where its color deficiencies will be quite noticeable and unacceptable in comparison. For this reason, to pick the right LED luminary for a particular job it helps to have a thorough understanding of the technology. For our company newsletter I have put together an overview of the technology and what products are available for motion picture lighting (available at ScreenLight & Grip's E-Newsletter.)

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

Unfortunately this is not true. In fact, it was a bad experience that Daryn Okada, ASC, (a AMPAS Science and Technology Council member) had mixing a Phosphor White LED lite panel with tungsten lights on a studio set that lead to AMPAS undertaking their Solid State Lighting Project tests that have revealed the high CRI claims of LED manufacturers to be nothing more than the “emperor’s new clothes”. According to Matt Hurwitz’s article “It’s a Phosphorous World” that appeared in the June issue of ICG Magazine, Daryn Okada, first noticed color rendering problems mixing Phoshpor White LEDs with tungsten sources when he used a “Tungsten” LED panel to touch up a face on one talent mark of a tungsten lit set. As the story goes, he hid a small LED unit behind a chair, to add some glow to an actress’s face when she reached a mark where the keys had fallen off. “The manufacturer claimed the unit to be a ‘tungsten LED source,’” he recounts. “She stopped right in the doorway, where I had this LED, and looked fine. But when I got the dailies back, her face was totally magenta.” What’s worse, Okada says the image could not be repaired in post, because there wasn’t enough of the right color of light in the scanned negative for a color timer to bring out.

It is a common mistake to think that a custom camera white balance can correct for the deficiencies of LEDs in every situation. Take Daryn Okada’s situation above. Had Daryn Okada been shooting with a digital video camera, he would have noticed the off color of the LED source immediately. But, given the limited spectral output of LEDs, his ability to remedy the problem would have been limited. If he white balanced the camera for the LED source, the background of the room beyond the doorway that was lit by tungsten lights would turn very green. In a mixed light situation such as this, the only alternative is to match the LED source to the prevalent tungsten source with a custom gel pack on the LED head. But, since gels rebalance the spectral distribution of a light source by passing the wavelength of the color that they are, it is not practical to use gels to correct for these deficiencies either because there is not light of those wavelengths to pass in White Phosphor LEDs to begin with.

To understand why this is so, we need only look at a similar situation: the conversion of tungsten light to daylight using full CTB gel. As you can see in the Spectral Power Distribution graph of tungsten light, tungsten light is so deficient in the blue part of the spectrum that it takes a quite saturated blue gel to balance it to daylight. In fact, the transmission coefficient of full CTB gel is only 36%, which means that it passes only 36% of the source. That is why gelling tungsten lights is a very inefficient way to create a daylight source (a tungsten 1000w gelled with CTB becomes a 350W daylight source.)

If you look at a Spectral Power Distribution graph of a White Phosphor LED light, a gel pack that would match it to tungsten light would have to include a violet gel to extend its’ spectral output below 425nm. It would have to include medium blue, cyan, and turquoise gels to fill in the missing wavelength from 465-510nm. Finally it would have to include pink, red, and orange gels to extend its’ spectral output beyond its’ 600nm cut-off. All of these gels would have to be quite saturated, since there is very little, if any, output of these wavelengths in White Phosphor LEDs to begin with. Imagine how much light you will get out of a LED light panel with such a gel pack (LED light panels put out barely enough to begin with, and have no output to waste to such accurate color correction.) In other words, White Phosphor LEDS are so deficit in certain parts of the color spectrum that by the time you came up with a color gel pack to match them to a continuous light source like a tungsten light, the LED panel would put out very little light with all those gels on it.

The bottom line is that color gel packs, camera white balance, or digital intermediate timing can’t bring out a color if it isn’t there to begin with. Simply by nature of their discontinuous spectral distribution, even high CRI Phosphor White LEDs will never accurately reproduce colors on screen regardless what you do on set or in post
Kino Flos, on the other hand, have a much more continuous spectrum. Once you filter out their green spike with minus green (magenta gel), they are able to render flesh tones more accurately than LED lights. For details, see my newsletter article available at ScreenLight & Grip's E-Newsletter.)

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

In the case of LEDs, color meters, like the Minolta III F, are completely useless. The meter makes its calculation of the color temperature based on an assumption that the light source has a continuous spectrum – LEDs don’t. Color readings of an LED have been shown to be misleading for both correlated color temperature and green/magenta shift because of their discontinuous spectral output.

Another drawback to White Phosphor LEDs is that their color output is very inconsistent. That is because their color output is affected by a number of factors: the binning and manufacturing tolerance of their blue pump, the thermal management of the fixture, the ageing of the phosphors, and even the ambient temperature. For example, a one degree shift in the junction temperature of the blue InGaN LED (pump color) in remote phosphor LEDs, will cause a +/- 2nm shift in the dominant wavelength. If compounded by the average wavelength variation of +/- 2nm of blue InGaN LEDs, a 5nm divergence from the prescribed 455nm wavelength of the pump color will create color inconsistency of 5 MacAdams ellispses. While not readily apparent to the eye, image capture systems will easily see this variation.

And, as broadcast studios lit exclusively with Phosphor White LEDs are finding out their output depreciates overtime and their color shifts much faster than the manufacturers say. The useable lamp life of Phosphor White LED luminaries designed for motion picture lighting applications is probably no more than 1500 hrs. To put that in perspective, it is the equivalent of burning through two HMI globes. Since these types of LED fixtures have no interchangeable parts that can be replaced after reaching low-light failure, after 1500 hrs the fixture can only be thrown away while an HMI head can be lamped with another bulb.

You have to be wary of all the claims made by LED head manufacturers because they all put a little spin on the scientific data which has a tendency to cloud issues. For this reason, it helps to have a thorough understanding of the technology. For our company newsletter I have put together an overview of the technology and what products are available for motion picture lighting (available at ScreenLight & Grip's E-Newsletter.)

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

But Guy, your always incredibly thorough research and white papers notwithstanding, what I was saying that IS true is that these units are out there working and producing results all over the industry without causing consistent problems. Obviously if they were, we wouldn't be using them. Daryn's issue as described could just as easily have been duplicated with, say, a Diva; I've had plenty of issues over the years with those going magenta on me. We all know that the green/magenta shift is not going to be anywhere near as noticeable to the eye as on film (video will tend to reproduce it similarly to the eye). I am regularly mixing tungsten, kino and LED's and I don't see ill effects. I just finished a pilot where I used the Litepads from Litegear as a beauty fill, either under lens or near lens axis. Their "tungsten" ribbon has a green cast and I use 1/4 minusgreen to correct it out. I watch at the monitor and dial the Litepad up and down to the appropriate level. If there was something "evil" happening in the spectrum, I'm not seeing it on the monitor--and in a WYSIWYG world of digital acquisition, what else do I need?

I'm not saying that LED is the be-all and end-all, I use it as a tool along with everything we've always used. I'm not giving up on tungsten yet. I'm just not sure what to do with this information being that empirically speaking, I'm satisfied with what I'm getting. It's a little bit like the naysayers with the DSLR's--on paper the specs are substandard, but the proof is in the pudding; a ton of great work has been shot on them. At some point you just have to get the work done, and in this day and age, speed and flexibility is key. I can (and do) stick the Litepads just about anywhere and get a good result far quicker and easier than I used to with non-LED technology.

This all said, it's interesting to learn about and I will keep an eye on color rendition in the tones you mentioned to see if I can detect issues.

Re: Florescent and LED spectrum is nowhere near flat
 

Sorry, pet peeve of mine. The "correct" quote seems to be: All the proof of the pudding is in the eating which at least makes sense. That quote is often attributed to William Camden, who wrote it in his Remaines of a Greater Worke Concerning Britaine, 1605. An old quote very often misused.

Re: Florescent and LED spectrum is nowhere near flat
 

Excellent Bruce! Consider me corrected and I will spread the gospel!

However: considering that LED's deliver such an apparently disorganized spectrum, is it not perhaps accurate to apply such a misquote to them?!

Re: Florescent and LED spectrum is nowhere near flat
 

Here's some thoughts that come up for me as I see this "revived" thread.

1). I can't particularly speak for other manufacturers but we don't claim LEDs have a high CRI. I just looked at the Litepanels site and I don't even see mention of CRI. There are probably some that do call it high CRI. Its real simple, if there is a color rendering problem they aren't high CRI. Most people using digital mediums today and LED fixtures are not having a problem, are white balancing and using filters and not seeing any big issues. They seem to want to say in the study that filters don't work and yet people using real film have been using this filter method for decades to correct on location lighting like parking lot or office flos, street lights, etc. How was it they got along till this study came out to tell them they're wrong? Filters may not correct a spectrum but they do correct bias and that's more than enough for most uses.

2). Far from trying to cover up anything, we've been at the forefront of education on this subject. We published at the time of release of the LED 600 some articles on LEDs in our site blog in early 2009, long before the AMPAS study came out in late 2010. We've also talked about it many times on sites. Here's one recent thread in particular which even links back to threads that go back to like 2008:

http://www.dvinfo.net/forum/photon-m...weirdness.html

This AMPAS study is primarily showing the response of LEDs and other sources on film. They barely scratched the surface of talking about what happens with digital. How many here, other than Charles, are still using real film a lot (or have ever used real film stock for that matter). I think in the study, they used a Dalsa Genesis (defunct digital motion picture camera) and a Nikon D7000 in a couple of tests and they barely talked about it at all--not particularly widely discussed or used cameras either. Why is that relevant? This is a site primarily talking about mainstream digital cameras motion and still. Digital is used more and more everyday and film less and less. That's a very elite group now and getting smaller all the time. That population here that deals with real film stock is very small compared to the users that use nothing but digital. So the response of lighting to film isn't very relevant to talking about the WYSIWYG world of digital except as an academic topic--and to definitely note, that there are differences between the two mediums. For example, digital is modeled after human perception and has a built-in mechanism for compensating for over-bias in lighting. In other words, a white balance takes care of most issues and if there is some issue of missing color in the spectrum it doesn't come up as an issue for most productions except the most critical. Whatever shift there is is mostly taken care of by taking out the bias of the light in the white balance. On film (which is not even close to human perception and the results had better be well engineered by people that understand how to make it work) the "white balance" so to speak is built in so its appropriate to talk about these issues for film people as they have other problems they have to deal with that digital people don't. I would even go so far as to say there could be a CRI rating for film and a CRI rating for digital. Again, digital is modeled after human perception and so is the CRI rating system. Thus CRI is very relevant to digital users. Not so much for film users. They totally have to understand how light affects the film stock they are using or they will have bad surprises in store when the dailies come back. If a light that is called high CRI isn't working on digital, then it simply isn't high CRI as claimed. The effect of the same light will be even more pronounced on real film given the way it reacts to discontinuous lighting like flos and LEDs (among others). Real film users should already know this however. Seasoned pros have had to deal with these issues for decades. And who would be using film that isn't a seasoned pro? The non-WYSIWYG nature of film doesn't tolerate or suffer fools very well. Mistakes are expensive. With digital you can see the results immediately if you want and correct anything right away. These issues with lighting and real film have existed as long as color film and discontinuous lighting have both existed at the same time which is pretty much since the 50s but the 60s in a more mainstream way with filmed color television dramas. Flos and LEDs are basically the same technology so why would you expect anything different? Knowledgeable film people would already be treating LEDs like they did the lower CRI flo and metal halide counterparts they've had to deal with on location for decades.

3). In the study they used 3200K tungsten lighting as the "reference" for their film shots of the color charts. Flipping it around to a more relevant subject here on this primarily "digital" site, there is no proof that using 3200K lighting with digital would be a good reference. Most sensors I know about were optimized for the daylight range. In a perfect world, color rendering is not affected by color temperature and is more related to spectrum. There is no perfect world however so tungsten lighting may not be all that optimal for digital given the way the sensors are optimized for daylight. Many have said they feel that 3200K (heavier on the RED side of the spectrum than on the BLUE) lighting which lacks in exciting the blue channel of a digital sensor leaves something to be desired. The point of this is, if you were to do some tests yourself using your digital camera, what would you use as a "perfect" reference? Where is the proof that your reference shot (with tungsten) is the real color to compare against other lighting with your digital camera? I hope you won't use tungsten. Even high CRI flos aren't all that perfect in their spectrum, there are always spikes of one kind or another. Probably need to use real sunlight, but then how would you light the other Macbeth chart with the test fixture using this split chart idea where both reference and test are shot at the same time?

4). Cool Lights LED fixtures weren't a part of the AMPAS test--not sure why we get several mentions in Guy Holt's post like we were there somehow. I saw clearly in one of their BTS scenes a Litepanels 1x1 was there along with some Arri tungsten fixture. I don't know what else they used, they didn't even bother to mention it. How scientific is that? Its basically over-generalization in the packaging of a "study" and they barely scratch the surface of how digital reacts to light. Perhaps relevant to their small group of film users but not so relevant to most of the rest of the world which is now using digital mediums. Probably the spectrums of most LEDs are similar but there will be some that are better than others. Certainly I've done tests recently with real, high CRI LED phosphors and I think they stack up every bit as well as the high CRI fluorescents that many have been using with great results in the film and TV world for about 21 years or so. Now we just need the price of said phosphors to come down so we can enjoy them in LED lighting like we do in fluroescent.

Re: Florescent and LED spectrum is nowhere near flat
 

I don’t deny that LEDs are a valuable tool in certain circumstances and can’t be mixed with other sources. For a specific application, say where lights must be operated off of batteries, a LED fixture offers the unique advantage of greater power efficiency over conventional lights, which may out weigh its shortcomings in color rendering. However, a Phosphor White LED is clearly not the best choice in applications where color rendition is critical. For instance I wouldn’t try to light a table top food/product shot with them. Because of their limited color rendering capability, food presentation that will look vibrant and colorful to eye under LEDs, will tend to look a little dull under on camera. By comparison a full spectrum daylight source such as HMI or LEP will capture the vibrant colors.

Or, imagine you were shooting an Air India spot and the uniform of the first class stewardesses were the blue/cyan dress in the AMPAS test I mentioned above. One would think LED light panels would the perfect choice because they are small, flat, soft, and hence ideal for lighting the inside of an airplane. But, in such a situation the Air India reps would be concerned by the fact that the subtle blue/cyan hues of their stewardesses’ uniforms are not being accurately rendered on screen where they would be if they were lit with true tungsten sources (side by side comparison available at ScreenLight & Grip's E-Newsletter.)

I also wouldn’t try to mix them with a uniform continuous light source, such as a studio lit with tungsten fixtures, where if caught in isolation as in Daryn’s case, their color deficiencies will be quite noticeable and unacceptable in comparison.

But, with a Diva, once you have corrected for the magenta shift, you have a nearly full spectrum source. With LEDs, it is nearly impossible to correct for their deficiencies with gels.

I wouldn’t think you would see the color rendering deficiencies of LEDs when used as a fill in a mixed light situation. I am talking about situations where LEDs are used uniformly or when seen in contrast to other sources in the same frame. I am not saying that you can’t use LEDs successfully. As long as you understand the limitations of the tools you have at your disposal you can do good work. But, in the case of LEDs it helps to have a thorough understanding of the technology to avoid bad situations like those discussed above.

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental & Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

Here's an easy test for everyone.
1. Get a color chart, one that shows vivid red, green, blue, cyan, yellow, and magenta.
2. Light it with tungsten 3200K, then white balance for 3200K.
3. Look at the results in post. (Preferably with a vectorscope) The colors should look fairly accurate, and can easily be corrected in post.

4. Light the same color chart with LED or flo, then white balance.
5. Look at the results in post. In most cases, you'll see some colors that aren't quite right.

If you try to color correct for those inaccuracies, you'll throw off the balance of everything else. Your conclusion will be that obtaining accurate color with LED or flo is impossible or near impossible.

Re: Florescent and LED spectrum is nowhere near flat
 

...then move on to PART TWO of the mental exercise...

LOOK at your scene. If you're shooting fashion and you have a bunch of purple and ecru scarves that MUST render color accurately - then bite the bullet and leave your limited spectrum choices behind.

But if you're doing a video interview with anyone OTHER than Elizabeth Taylor (those violet eyes?) then save the weight, power draw, and hassle of taking along gear that is over-heavy and inefficient since you can likely get a PERFECTLY acceptable interview shot - and save yourself a lot of hassles in the process — with Divas or even LESS expensive and power hungry LED solutions.

Sure you MAY knowingly devalue PERFECT color rendering. But sometimes that's a perfectly sensible trade, particularly if you know in advance that the the specific spectrum colors that a technology does not do particularly well are NOT a critical part of your shots.

THIS is the point of experience, folks. It's knowing enough to evaluate a scene - figure out a proper approach to that particular scene, and then to choose to do that which makes the most sense for THIS shoot in THESE conditions.

Or heck, go ahead and believe that your venerable Arri Tungsten kits, "portable" gennies and half a dozen sherpas is the ONLY way you can get great results on your next video gig. I just hope for your sake that it's not a gig titled - "Let's Go Climb Yosemite"

They knew better a few hundred years ago when somebody first mumbled "horses for courses."

Simple as that.

Re: Florescent and LED spectrum is nowhere near flat
 

Bill, your "horses for courses" phrase has been echoing through my mind many times, and is I think a good way to approach these deficiencies. Everything has deficiencies, and it's a matter of choosing which ones you can get away with for a particular project.

I just got an SSD hard drive for my laptop, and love it, even though it has some glaring deficiencies like small capacity and high cost.

Guy has done some really great work in putting this information together in a digestable format, and I think it's useful especially for those who work with LED and flo lights, to understand what issues to look out for and work around.

I just bought a third LED panel from the same manufacturer as the first two. I was very glad that I had the opportunity to go into the store and look at these in person, because I discovered that the smaller size I was planning on getting had a significantly different color, different enough that it would have made mixing them problematic. This despite the fact that these were all lights in the same series from the same manufacturer. Even the store employee was surprised to notice the difference.

I instead got a third LED panel in the same exact size/model as the first two, and indeed the colors match. But the uniformity of the LEDs is much worse than the first two panels; some LEDs are brighter than others yielding a speckled quality, whereas the original ones I had are uniform. It doesn't affect functionality, but it goes to show how LEDs from different lots clearly are not the same, even when from the same source. Guy's paper goes into the issue of sorting and binning LEDs to achieve consistency.

No need for us to disagree. There can be serious issues and still be good enough for many purposes.

Re: Florescent and LED spectrum is nowhere near flat
 

Tom,

I agree with what you wrote wholeheartedly.

The big issue is that it's an age where many people are coming to video production with a "do it yourself" mentality - which is excellent. However, often this is combined with a "just point me to the piece of gear that will do this thing I want done automatically, and professionally, whenever I throw the switch" - and such things have always been fantasy.

THAT is the problem. People think that making video is done with things akin to an iPod, the magic of which is that it appears at first blush to be a stunningly easy machine to operate. Press a button and you get beautiful music. You do - and that instant satisfaction is sweet. But as you get to know it, you face the issues of music purchase, library management, interfacing it to something other than headphones, battery life - and the seduction of simple yeilds to the complexities of the reality that you're doing something much more complicated that it looks at first blush.

Lighting is the same. The new folks want "buy this LIGHT you can light anything." and that's the same as saying "buy this piano and you can play anything." It's true in a sense. It just neglects that small step of actually becoming a piano player!

Re: Florescent and LED spectrum is nowhere near flat
 

The piano player analogy is apt, but I would suggest that the iPod one is less so, in that the structure of working with an iPod is essentially finite. Yes, there is more to it than pushing one button, but it can be mastered by most in a fairly short amount of time, and once you learn the structure, it's a matter of simple repetition to achieve the desired results.

Lighting is an open-architecture pursuit; while there are basics to learn and apply, there will always be variations presented by circumstances that can and should inspire one to always keep trying new things. I don't doubt that the vast majority of shooters go about lighting headshot interviews exactly the same way every time, and that being one of the more simple setpieces in the book, it's not surprising. But at the same time, those who care to pay more attention learn that the exact height and angle of each source will have a specific effect on the results, and because each person is different, it's critical to understand this to make them look their best.

Agreed that there is a perception out there that there must be shortcuts to all of this, but fortunately some aspects of filmmaking are immune to the immature, entitled thinking that advances in technology have made filmmaking "easy", and lighting is one of these. There is no substitute for learning by doing and observing.

For me, the very fact that I have and probably never will "master" the art of lighting is what keeps me interested. Every setup I shoot, I draw on 25 years of personal experience but the results are rarely 100% predictable and I'll take away something new every day.

For the record, for interiors and night work I still light primarily with tried and true tungsten, but I like the space-saving and speed aspect of Kinos and the even faster and more flexible aspects of LED's.

Next time I'm shooting camera tests I'll have to experiment with each of my LED units and see how they fare with the Macbeth charts.

Re: Florescent and LED spectrum is nowhere near flat
 

You really need to test with the meduim you're using. Video cameras have traditionally been pretty blind towards the green in standard fluorescents, whilst with film the green does come out pretty strongly. You need to test with the camera you're using to see how it's responding with the greens, some of the new digital cameras may pick up green because they not limited to rec 709.

Re: Florescent and LED spectrum is nowhere near flat
 

No truer words have been spoken, but there are a couple of important differences between Kino Flos and LEDs that are pertinent to this discussion. One: the discontinuous color spectrum of Kino Flos can be easily corrected with gels, LEDs can not, making Kino Flos a better key source, in my opinion, for documentary interviews because they will render flesh-tones better. Once the green spike of Kino-Flo’s True Match tubes have been corrected by the application of minus green (magenta) gels, the resulting spectral distribution is nearly continuous and contains a greater proportion of the long wave length colors that are so critical to rendering flesh-tones accurately. As can be clearly seen in the side-by-side comparisons in my newsletter article, skin-tones are significantly altered by the steep drop-off of long wavelength colors in LED light sources. Kino-Flo’s high CRI True-Match tubes, on the other hand, contain sufficient light in that critical part of the spectrum to render skin-tones realistically. Once corrected for their green spike, Kino Flo True Match tubes provide a nearly full spectrum source. With Phosphor White LEDs, it is nearly impossible to correct for their deficiencies with gels. To see side-by-side comparison go to ScreenLight & Grip's E-Newsletter.

The second distinction is that while the out-put of both sources depreciate overtime, when you reach low light failure of a Kino Tube after 2500hrs you can simply replace it. The useable lamp life of Phosphor White LED luminaries designed for motion picture lighting applications are probably no more than 1500 hrs. Since these types of LED fixtures have no interchangeable parts that can be replaced after reaching low-light failure, after 1500 hrs the fixture can only be thrown away (see ScreenLight & Grip's E-Newsletter for more details.)

- Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental & Sales in Boston.

Re: Florescent and LED spectrum is nowhere near flat
 

We've had LED 600s out for 2 1/2 years now. No "low light failures" that we've heard of. The LED 600 is completely modular and if a customer wanted to upgrade or change out an LED panel, dimmer or battery interface for whatever reason they could even do it themselves or have us upgrade it for them for reasonable fees. I anticipate that as LEDs improve in output or spectrum, people may do just that.

As far as color is concerned, see post #19 in this thread. Bill Davis, who Guy told to "forget about Cool Lights", was showing some work he did with our LED 600 which he's had since they came out. Said he didn't even use any correction on the fixture.

http://www.dvinfo.net/forum/photon-m...irdness-2.html

I don't see anything wrong with that photo, where's the problem?

Re: Florescent and LED spectrum is nowhere near flat
 

Then why are online production forums filled with posts like the following:

“The few times I have been around LED's, the green spike or blue leaning color issues were unacceptable. Two weeks ago I was on a doc/interview shoot that was using some and the skin tones on the RED's monitor were very green.” Read more: Any truly color accurate LED panels out there? - Cinematography.com

The problems with LEDs go beyond color rendering. We have noticed that they cause interview subjects discomfort. John Rossetti, a well known DOP in London recently related on the Cinematographer's Mailing List : " It does not matter how many LED's there are in the head, its still a pointsource, from the talents point of view.... I have had some well known names refuse to be lit by them" (full account available at Message.) Having personally lit a number of Senators and even one President I know that the rendering of skin tones and the multiple shadows created by LEDs are on the radar of political media consultants. How are you going to look when the media handler for a Senator tells you that you cannot use them to light the interview.

The industry didn’t “(get) along till this study came out to tell them they're wrong?” Anyone that has worked on dramatic productions, be they well crafted dramatic shorts, commercials, episodic television, or feature films shot on film or digitally will attest that they have NOT been “using this filter method for decades to correct on location lighting like parking lot or office flos, street lights, etc.” I have spent many an hour changing out office fluorescent tubes for Movietone tubes, changing out CFLs for PH bulbs, replacing sodium vapor bulbs with tungsten bulbs in streetlights, and wiring tungsten peanut bulbs behind lamp posts. Why? Because the color deficiencies of these light sources could not be corrected by simply slapping on gels. The AMPAS study only confirms in regard to LEDs what we have known for years about these other light sources.

If only this were true. Unfortunately the reality is that camera white balance CAN NOT correct for the deficiencies of LEDs in every situation. Take Daryn Okada’s situation above. Had Daryn Okada been shooting with a digital video camera, he would have noticed the off color of the LED source immediately. But, given the limited spectral output of LEDs, his ability to remedy the problem would have been limited. If he white balanced the camera for the LED source, the background of the room beyond the doorway that was lit by tungsten lights would turn very green. In a mixed light situation such as this, the only alternative is to match the LED source to the prevalent tungsten source with a custom gel pack on the LED head. But, since gels rebalance the spectral distribution of a light source by passing the wavelength of the color that they are, it is not practical to use gels to correct for these deficiencies either because there is not sufficient light of those wavelengths to pass in White Phosphor LEDs to begin with.

If the actress in Daryn Okada’s shot were the model in the blue/cyan dress posted in my newsletter article, you can imagine what would happen when she stepped onto the mark lit only with the LED source by looking closely at the contrasting photos in my newsletter article. Since, under the circumstances, Daryn Okada could not white balance for the LED source (and it would not be feasible to match the LED source with a gel pack) the rich blue/cyan hue of her dress in the left photo would turn into the simple blue of the right photo. The vibrant skin tone of the left photo would turn into the flat skin tone of the right photo, and it would have an overall magenta cast to boot.

The bottom line is that color gel packs, camera white balance, or digital intermediate timing can’t bring out a color if it isn’t there to begin with. Simply by nature of their discontinuous spectral distribution, even high CRI Phosphor White LEDs will never accurately reproduce colors on screen regardless what you do on set or in post. Kino Flos, on the other hand, have a much more continuous spectrum. Once you filter out their green spike with minus green (magenta gel), they are able to render flesh tones more accurately than LED lights. For details, see ScreenLight & Grip's E-Newsletter for more details.

Only in so far as humans are basically the same as whales because we are both mammals. You make the same self serving reductionist argument on your website in regard to HMI and your CDM (Ceramic Discharge Metalhalide) fixtures. LEDs and high CRI Fluorescents couldn’t be more different. For one thing, the discontinuous color spectrum of Kino Flos can be easily corrected with gels, LEDs can not. Once the green spike of Kino-Flo’s True Match tubes have been corrected by the application of minus green (magenta) gels, the resulting spectral distribution is nearly continuous and contains a greater proportion of the long wave length colors that are so critical to rendering flesh-tones accurately. As can be clearly seen in the side-by-side comparisons in my newsletter article, skin-tones are significantly altered by the steep drop-off of long wavelength colors in LED light sources. With Phosphor White LEDs, it is nearly impossible to correct for all their deficiencies with gels.

Richard as much as answers his own question in the same paragraph when he states “the spectrums of most LEDs are similar but there will be some that are better than others.” The Litepanel and Arri LED panels used in the AMPAS tests being the better ones because they use more stringent criterion in the binning of the LEDs they use which accounts, for a large part, why they are more expensive. I mention Cool Lights LED panels among the others because they also use Phosphor White LEDs with the same deficiencies in color output.

For one, he looks awfully pasty and pale for a Texan. The skin tone in Bill’s photo is consistent with the results one would expect when lit with an LED source. Absent the long wavelength colors above the 600nm cut off of Phosphor White LEDs, the flesh tone lacks “color” or vibrancy. I don’t deny that LEDs can be a valuable tool in certain circumstances. For a specific application, say where bulk and weight when traveling is a factor, a LED fixture offers the unique advantage of being compact and lightweight (but then so are Kino BarFlys.) Under the circumstances, for Bill this advantage to LEDs out weighed their shortcomings in color rendering. Bill says as much in this thread:

“… you MAY knowingly devalue PERFECT color rendering… sometimes that's a perfectly sensible trade, particularly if you know in advance that the specific spectrum colors that a technology does not do particularly well are NOT a critical part of your shots.”

For example if you were to look at the image of model in the cyan/blue dress lit by Phosphor White LEDs in isolation, you wouldn’t know that she doesn’t look like that and so wouldn’t think it was a “bad” likeness. But, when viewed side-by-side with the same image lit by a continuous tungsten source, you see what it should have looked like (the side by side comparison is available in my newsletter article.)

As Bill rightly points out, the value of experience is knowing how “to evaluate a scene - figure out a proper approach to that particular scene, and then to choose to do that which makes the most sense for THIS shoot in THESE conditions.”

When I read posts, like Bill’s (#32), from working professional DPs (as opposed to newbies and salesmen), I don’t hear them saying that “people using digital mediums today and LED fixtures are not having a problem, are white balancing and using filters and not seeing any big issues.” I hear them saying there is a problem. So choose the appropriate lighting technology for the job and clearly Phosphor White LEDs are not the best choice in applications where color rendition is critical. For instance, Bill himself says in this thread: “If you're shooting fashion and you have a bunch of purple and ecru scarves that MUST render color accurately - then bite the bullet and leave your limited spectrum choices behind.”

I, for one, wouldn’t try to light a table-top food/product shot with them. Because of their limited color rendering capability, food presentation that will look vibrant and colorful to eye under LEDs, will tend to look a little dull on camera. By comparison a full spectrum daylight source such as HMI or LEP will capture the vibrant colors.

Likewise, when I lit Ted Kennedy in his old age and his media handlers wanted to convey the impression of a robust and healthy elder statesmen, I fought to use an HMI interview kit, with its additional weight and cost, when the show producers wanted me to use a cheaper LED kit. To convince the Producers I brought the LED kit, and after seeing the results they came up with the extra money for the HMI kit because it was important to render a healthy flesh tone.

I also wouldn’t try to mix LEDs with a uniform continuous light source, such as a studio lit with tungsten fixtures, where if caught in isolation as in Daryn’s case, their color deficiencies will be quite noticeable and unacceptable in comparison.

I am not saying that you can’t use LEDs successfully. As long as you understand the limitations of the tools you have at your disposal you can do good work. But, in the case of LEDs it helps to have a thorough understanding of the technology to avoid bad situations like those discussed above. For this reason, I have put together an overview of the technology for our company news letter (available at ScreenLight & Grip's E-Newsletter.)

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

Re: Florescent and LED spectrum is nowhere near flat
 

Guy, I wasn't quite sure how to evaluate the RGB LED results in the graphs you posted--seemed like the spectrum was even choppier than the white ones. Have you tested the Zylight, for instance?

p.s. you get a special bonus for bringing your answer in under 500 words...!!