Is CRI really dead?
 

I found the following excerpt from a lighting manufactureres website. Now I consider the statements about CRI not being very important complete bunk but it does raise a question, are the new cameras so good that bad lighting (color wise) doesn't make as much of a difference as it used to? There is so much more to a high CRI rating than just color temperature. I feel that the better the light quality the better the image, and being able to match light sources with a given standard is important.

Interested to see what others think about the importance of CRI.

-Start quote
"The CRI rating of light sources, is an old out-of-date standard developed by the International Commission on Illumination (CIE). It is a relative index which compares the relative color reproduction ability of one light source to another for a standardized FILM medium. The maximum value of 100 is given to tungsten light sources, therefore all other light sources including sunlight will have values less than 100. This was an important reference for film photography because tungsten balanced film rendered perfectly in tungsten light and color shifted for almost all other light sources that have lower CRI values.

This outdated light valuing method is mostly irrelevant to digital photography because all digital cameras include compensation for color temperature and are more accurate at 5500-6000K than the 3200K color temperature of tungsten light. In reality tungsten light does not render very well as it has an abundance of red and infrared (heat) and is relatively weak in the blue part of the spectrum. In reality, light sources that are closer to 5500K (like the XXXXX Lites) will render color better in a digital camera than tungsten light.

Conclusion: We include CRI ratings in our product descriptions because many customers request it as it is the only reference commonly used. But in terms of using CRI to determine the rendering ability of a light source CRI is useless. In reality we are anxiously waiting for the CIE to develop a better index that address the many light generation technologies present today that are far better than tungsten sources."
-End quote

Hi Chris.............
 

Gonna try not to dig myself a big hole on a subject I know little about, but this has me a bit stumped:

"There is so much more to a high CRI rating than just color temperature"

Er, what, exactly?

If a CRI rating is measured entirely against Tungsten, with it's preponderance of red and absence of blues, how can it have any relevance whatsoever to what renders best in digital imaging systems that don't use silver as the imager?

From my reading of your quoted article, the whole basis of the CRI related to FILM, not digital, and they go on to say that the standard is basically out of date with current technology.

I won't argue with that, 'cos I can't. It is (out of date for digital imaging).

Good as the new digital cameras (still or video) are, I've yet to find one that will render colour correctly (no matter how analy it's WB has been set) with pure tungsten lighting.

Whether the "XXXXX Lites" from manufacturer "X" are any better, is another question entirely.

The CRI system was thrashed out between film manufacturers and lighting ditto over many years and served the industry well for a very long time indeed.

It's now "all change" on the camera front and there needs to be the same in lighting as well.

That's my take, for what little it's worth.


CS

CRI wasn't thought up for film or media production use at all. Its a rating for all lighting manufacturers to use. Its not really dead until another system comes into place to replace it and every one accepts it.

Real film people think its important because they have no way to filter out the extra green found in lower CRI lighting other than minus green. A lot of people brought up under film people therefore think its important even though they it may not be a concern today with so many using digital mediums.

Video/digital media use has made it super convenient and many times the custom white balance on a camera can take care of any infractions in the green/magenta balance, getting it back into order.

Whether you add more magenta inside a bulb in the form of extra phosphors, magenta outside in the form of a minus green filter or compensation in the white balance, they are all pretty much accomplishing the same thing for digital use. Some kind of filtering is coming into play one way or another. For film people, the first two are their only choices since film and film cameras have no nature filtering ability built in.

I to am not an expert, just interested in finding the best colour quality and knowing how to tell it when I find it.

CRI is more than just a colour temp rating, it’s a rating of how well a given light source renders colours to the eye, or camera in this case. It considers the emission of full spectrum light, free of nasty spikes, and the smoothness of the spectral curve covering all of the given wavelengths of light in a light source. The fuller and smoother the curve the “nicer” the light looks to the eye and the camera.

I think when using digital cameras as soon as you put up a white card and carry out a white balance procedure on your camcorder, you are immediately altering the red, green and blue values of the cameras three CCD chips (not sure how this works with CMOS), this can result in inferior skin tones and other colour inaccuracies. Digital cameras internal white balances are biased towards corrections on the green/magenta axis but the chips see in RGB, to my little mind it seems the digital white balance is leaving out some of the spectrum from its correction that makes for less than perfect skin tones.

True the tungsten standard has colour peaks but they are smooth and full spectrum. It may not be the colour your looking for but it is a standard, with modern cameras a click here and a quick gel there and great looking video can be recorded even with the limitations of digital white balance – film guys aren’t so lucky. With higher CRI light sources less gelling will be needed and thus light powers can be lower or fewer fixtures used to get the same light level as well.

Oh well, just more material for the water cooler debates.

By the way, CRI and color temperature are unrelated. You have two measuring axises in light: red/blue and green/magenta. Color temperature is rating of the particular shade of white light with a bias between red on one end (3200K for instance but of course goes much lower) and blue on the other end (5600K for instance and beyond). CRI can indirectly be related to the green/magenta axis. The more out of balance on the green/magenta axis (either toward green or magenta bias) the less the CRI. The more in the middle of the scale, the closer to 100 you come. You can easily have a 5600K light that's a bit green (lower CRI) and you can also have a 5600K light that is in balance (high CRI). They're both still 5600K though.

On the subject of full spectrum. There's only really 3 full spectrum sources I know of: tungsten, daylight and carbon arc. Other than that, anything else that claims to be full spectrum is more of a simulation of full spectrum but if you actually look at the readout taken from an integrating sphere of the particular light being measured, you'll find it to be mostly pretty spikey in red green and blue and the rest of the spectrum more shallow.

Ahh the ol' integrating sphere , not your standard meter in everyones bag of tools. Thanks for the input. Still anticipating the arrival of my Kenko 3100 colour meter you reccommended Richard, gonna see what trouble I can bring to the next shoot for the grips.

I think there's a lot of truth in the statements but the conclusions are the opposite.
With the narrow emission spectra of some modern light sources we should be looking at the spectral emission curves rather than relying on averaged numbers.

That's true but many wouldn't really understand what its telling them. In this day and age, people want a quick way to sum things up, make it easy to understand and unfortunately CRI is the quickest way to communicate this until someone else comes up with a way to sum up the spectral output.

Can you (or someone else) go into a little more detail about the "many times" part? Is it that some cameras custom white balance better than others? And/or are there circumstances whereby the custom white balance works better than other circumstances? Thanks! -JP

Johnathan,

One excellent example is in shooting in mixed lighting situations.

Imagine a set where you have reception area with daylight admitting windows. Then, beyond the reception counter you have a inner workspace lit by fluorescent fixtures.

Your camera takes a "white balance" on the entire scene which - due to the mixed light, is less than satisfactory. No matter HOW sophisticated the camera's internal white balance circuitry - you have a problem - because no camera that I'm aware of can set some of the CCD pixels to one WB and others to another.

So you're faced with telling your camera what YOU want. Do you want to skew to take the green spike out of the inner office - at the risk of making the reception area and it's people look too "ruddy?" Or would you prefer to balance on the reception area people and let the inner office people look sickly green?

Your choice.

If I can add one other note to the discussion - one reason that Tungsten -for all it's inefficiencies in converting electricity into light stays with us is that the technology is so well understood.

Pop on line and you can find tungsten to daylight conversions anywhere. Tungsten is a standard.

Daylight, on the other hand is pretty arbitrary. What kind of daylight? Daylight at 12 noon? Daylight at 5pm. 5pm where? Northern or southern hemisphere? Is it daylight through clouds? What kind of clouds? Silky stratus or threatening clumulus? Is it daylight reflecting off the white sands of New Mexico? Or bouncing off the blue walls of the restaurant next door?

With sunlight, you're constrained by using it as it falls on your scene. Adapting or filtering it is typically a hassle often involving giant silks, sandbags and large crews.

Tungsten is a snap by comparison.

BTW, Richard. Maybe you should look into a line of carbon arc fixtures! I kinda miss the smoke and heat of my days as a Strong Super Trooper follow spot operator back in High School!

Hehe, I ran one of those in College. Terrible is the best way to sum it up from an operator's viewpoint. HMI was someone's attempt to redo it better but not completely full spectrum though like a real carbon arc. So now most all of those spots are retired and in their place is either a spot with an HMI bulb or a Xenon which is incredibly powerful but not necessarily all that efficient.

One thing I was curious about recently, sort of O.T. the original question. What was the color temperature of the carbon arcs used in filmmaking? In other words, what type of color temp film did they use when filming with predominantly carbon arcs? My guess is daylight but I was thinking though that carbon arc was actually not quite in the 5600K range though.

Jonathan, Bill said it. Mixed light situations confuse the camera white balance logic. Mixing color temps or simply mixing different kinds of light even within the same color temperature can be an issue or it may be no issue at all. Testing will tell you.

Another reason that using manual white balance is better is that many cameras only auto white balance within a certain range. For example the Canon auto white circuit has a lower limit of reading 3000K and many residential interiors lit by practicals are below that limit so AWB goes whacky. It's the Star Trek Ferenge (sp) yellow skin syndrome:)

but as said above , CRI and color balance are different things.
Good CRI is the warranty that if you expose a color chart, all colors will render more or less as they should relatively to each other. With bad CRI, you will get some colors to be ok (usually blue,green red) and some being totally messed up (usually yellow, brown, purple).
So you can adjust white balance to any value you want (and god knows that NO commercial movie is released with original colors), if some colors are ok and some are wrong, it is an heavy work to get them back ok.

As far as I can tell preset white balances like 3200K or 5600K don't necessarily have any green/magenta correction ability in them. You have to go custom to get that logic to kick in.

Ok, I get it about mixed light situations. So where the light is homogoneous it makes more sense to do a custom white balance. Like if you've got an LED source with a green spike, it seems a lot easier to just use the wb than to gel the source with a plus green, besides which you lose some light with the gel. I guess there are situations where you just can't do a custom white balance...anyway I just didn't realize that the custom white balance could do just as good a job. Really it should do a better job since you're often guessing when you use a gel...

That said, it seems safer to gel the source if you're in a mixed light situation...

Does this make sense?

If your in an environment where you are only dealing with two mixed sources, usually sunlight and something else, you have to decide which light source will be the easiest to control (or alter), and that often will make the choice for you. If you can eliminate or control some of the light and get it down to the least troublesome light to use I always take the easy way and match to that. Closing curtains, putting garbage bags or cardboard over windows is a pain but it eliminates the ever changing sunlight (or streetlights) and lets you then control all the light sources. The fewer gels the better as you have mentioned but if you are using flos or leds you almost alway have to gel.

Sure it makes sense to "gel the source" in a situation where you're facing mixed lighting.

But that's OFTEN not possible.

You going to gel the sun? Gel every square inch of all the exterior windows in an office suite. Gel 500 fluorescent tubes on the big factory ceiling?

Yes, people do this. For a big budget feature or for something of lasting value where the stakes are high, good gaffers do whatever it takes to control the lighting. I know a guy who for a twice a year shoot for a company that sells corporate jets, not only rents every Kino flo in this state, he imports more from California at well.

That's the point. Experience people light for the job. They don't buy a fixed group of lights then try to fit EVERY job to the capabilities of that kit. That's the road to mediocre results.

FWIW

CRI May be quite properly outdated...
some of the issues I see with CRI are the following- some of you have already commented on these, but I thought I would riff a littlle... Hope you dont mind!

CRI was based around colour rendering using Tungsten as the reference source, and does not really take in to account discontinuos spectrum sources such as HMI, Fluro, Or LED acuurately.

CRI Uses a small sample size (8 samples) to generate the averaged result .
These samples are typically all from low saturation colour samples and have an uneven spacing around the black body locus (the central line that runs through the planckian graph, along which is 'white' light)

Unfortunately, CRI can not tell you any info about which direction your light is incorrect, just that it is bad. (In the Film and Video, world a CRI > 90 good, CRI< 90 bad, which is not strictly the case. we need to look more at how our gear responds to actual colours rendered.)

I Agree with what Richard Andrewski said about green, unfortunately CRI has been the only thing that indicates if a light is deficient or dominant in some area for quite some time now (it was invented in the 60's)

I've Just written a bit of a blog on all things CRI, and also a bunch of links and images on the subject, if anyone is interested in having a look, the post is at http://tama.typepad.com/blog/2010/01...l-to-work.html

The good news is there may be a replacement for CRI in the Pipe, the Colour Quality Scale.
More samples from a broader range of saturated colours, giving more ballanced colour data..

Let me know if you have any thoughts or comments, would love to hear from you all !

Cheers,

Tama

Tama,
The link to your blog is not working.

Thanks Bob, It was momentarily down,as I linked to an accidentally created post that was a duplicate, then deleted. My apologies !

Here it is again, Or just click on my signature.


CRI, LED's, CMOS and actually getting it all to WORK. - Tama Berkeljon's blog

Cheers,

Tama

Well Tama, I must add as the instigator of this thread that your reply was exactly what I was hoping for.
Of course I appreciate all the other replies and insights but you have given me some food for thought, however I must tell you I disagree with a few of your statements, particularly about the colour bias of CMOS and other semiconductor materials-----BUT---- I'm going to double check my facts before I blurt out a reply as you have also turned a few of my thoughts around. I have been looking at the CQS system as well as discussions on an LED only colour standard from some of the major LED manufacturers and will chime in on those topics as well.
I anxiously await your postings of meter readings (or should I say mis-readings as you seem displeased with the results) from your work with non-full spectrum sources.
Now we’re cookin’
Cheers Chris

Thanks for the Kind words, Chris ! Your instigative question was one of the motivating factors for me to finish my blog article and get it out - sometimes I need a bit of a push !
When It comes to silicon devices- my example with the diodes is slightly exagerrated to demonstrate the point. silicon purity and homogenity govern the electrical characteristics of any piece of silicon, and because silicon has a grain structure that is variable due to purity, and has a cut thickness that can vary even by small amounts, my understanding is that these factors can affect the way silicon interacts- even by small amounts.

If anyone can clarify this further I would be very interested, as these are only my own observations and also the result of conversations I have had with material scientists who work in the field of silicons.. Not popular things to publish if you are in the business of making money from silicon chips, but as a designer or an engineer you may come across this quite a bit..

Cheers !

T

allintext: doped cmos etched - Google Search

i assume like a lot of the semiconductor things, they use the Doped and Etch type of stuff, to make the gate things. I have seen a video on the processes, and a person could say that the processes of making (at least some) semiconductor devices is what i call "organic"

we think of many of these things as locked rock stable made to microscope specs with robotics and clean rooms and that somehow every Atom in the process is exactally where it should be. instead the Microscopic surfaces of the semiconductors looks like rugged mountains of randomness, not perfect surfaces or aligned blocks.

They are all still made of highly purified elements of this earth, being eaten away by acids, coated with chemicals/elements , and other such "organic" processes, they dont physically or mechanically align every atom :-) Yet! The semiconductors i saw being made went through 6-10 processes cleaning, etching, doping, coating, cleaning, and back around again.

So i would ASSUME that is why a signal comming from each miniature photo diode gate thing (pixel), could vary one from the other, and especially when it is at its first "trigger point" the lowest light hitting it, where one item will react before another, and that being more noticable change from 0to1 vrses 50to52.
i assume, that is where color grain noise comes from as different locations trigger slightly different, add in that the filtered light waves trigger it, probably have randomness, and effect the triggering of the diode depending on where they land exactally.

all that can also be observed in many other semiconductor gates, like multi-emitter leds and transisters in processors and all.

So the whole array of collector items, would have variances among the "pixels" but each overall Cmos chip item, should be similar to the next one made in that batch. so the variation of each Pixel item would be pretty visable, the randomness there. but each of the whole chip items should be relativly the same.

like a Patch of organic DIRT :-) with different specs in it, but wide whole areas of dirt, that look similar to the rest of the dirt.
so each cmos of a batch should be overall similar to its brother in the bath.
then you have the chemicals , and baths and acids all changing over time, just like the batch of chemicals at 1Hr photo has to be changed up, cleaned, added to.

Why does Chip grain look like a small version of Silveroxide grain on Film , because they both have somewhat organic random distributed components reacting to light slightly differentally.

No i have no idea what i am talking about, but that is what i gathered from seeing many of the processes.

Oh the thread topic :-)
we now have 8 different "colors" of lights in/out of this one house, most with rotten Spectrums, many with Rotten "CRI" pan five feet and the color is different .

What is it going to be like when there are leds of 20 "white" shades, florescent of 10 types, 3 forms of incadescent, plus the wonderfull sun.
I wonder if they shouldnt start doing somthing NOW, about the camera overreaction (compared to human eyes) to the different colors and spectrums and lacks of CRI in the efficency lighting. Single color lighting is Dead, that is for sure.
ATW is not capable of coping with the differences at all.

Ouch! My head hurts now:)

I'm still digging up some info here but I'm sure in the end I'll conclude (and share) that any real issues with the colour interpretation of a CMOS is more influenced by the camera circuitry that lies beyond the CMOS sensor in the image processor circuits. Any influence by the CMOS's random manufacturing variences will be infintismal (sp) when compared to the influence of the image manipulating actions within a camera.

More on this later.

Thanks to Tama for bringing the proposed CQS standard to my attention. One concern I have is it relates to human perception of color which is not the same as how our cameras see color. Also the new standard uses more saturated colors and gives some weight to color differentiation as something desirable in human perception. Also of note it's been jigged so the existing fluro lamps get the same score to avoid confusing the public.

Certainly the new standard is better than the old, not certain though how much it will really help in our game and I sure lack the knowledge to translate how they are rating colors and the new color spaces being used, into how our cameras work.

Marty--I disagree! Single colour light is NOT dead, single colour fixtures maybe yes, but we have to correct existing fixtures to generate light that works for our cameras. We dont have to accept poor light unless we are lazy and dont want to get out the gel kit. Until they come out with a camera that can have multiple colour correction capabilities and a sensor that can activate the various options automatically as we change the light falling on the sensor our only option is to correct all the light sources until we are happy with their uniformity. In the very near future I think we will be seeing some fixtures that have very high effiency as well as very high CRI and full spectrums. Keep our fingers crossed until then.

CRI is not about light temperature. You can get an yellowish light with excellent CRI (but a yellow cast) and a white light with bad CRI.
fluorescent tubes or LEDs are known to give good white light with bad CRI, because the technology of exciting a gaz (giving mainly UV light) and transforming it into visible light by a photonic reaction (the chemical layer inside the tube or over silicon) can only give bad result (CRI wise). sodium vapour light is the worst example.
Mainly because this give burst of energy in particular wavelength (like laser are) .
So it can happens that almost all color can render correctly and only one color cannot render at all (giving a grey instead purple for example).
there are tons of color chart you can find showing the problem.
It is particularly difficult to correct because you cannot use regular color correction applied to all the picture. You have to set the pixels that are bad and replace them with good color.
and you cannot correct that in the camera either.

Even when they have LED with Multi Phosphors, which they are working on making as we speak. single Color Leds that gain thier efficency with phosphors just like the white ones do with phospors. meaning they can put groupings of RGB phosphor based leds in for lighting, in the same House , someone will have florescent there, and Some incan in the bathroom, or down some hall, or some halogen thrown in there.

The phosphors are what is making the light efficient in ccrt led and florescent, even when they pepper these things with different color outputting phosphors or mix groupings of different colors, there is spikes in the color areas, not a full spectrum. When they have a full spectrum, they arent "efficent" at all. a person could even say that efficency is just tricking the human eye. it just doesnt fool the camera :-)

using RGBYC leds on (say) the top of a video camera without phosphor based leds, takes almost as much power as a halogen :-(

Phosphors being energized outputting the photon things do not live forever, different phosphors die sooner/later than other, more or less of one type or the other are needed, and therefore, the one type is depleted before the other , , etc etc. so phosphor based (efficient) lighting with multicolor spiking phosphors will also change color over the life of the output item. So some stuff will look great on a chart today, and a year from now , mabey not so.
i think most people can observe that in thier phosphor based florescent lighting of different types and (original) CRI indexes. something a little different about that older bulb that has 7000 hours on it ?

Energy to light efficency isnt magic, the way they are getting energy to light AND being efficent about it has major ramifications to the spectrum, and untill they are all made by ONE huge corporation the ramifications are all different.

dead , it is dead untill they make the Fusion light and replicate the sun everywhere :-)
they have the Microwave Plasma light out, and its spectrum again different.

Sure WE can get lights with good "CRI" or just good RGB and send that RGB into 3 RGB chip things, but the stuff they are working on for efficent house and commertial lighting is all over the spetrum. Different things in different fixtures IS efficent by design of the fixtures themselves.

Over in the light forum, i dont see some standard Efficient lighting comming on the horizon, i see 50 different ones, each with thier advantages and disadvantages, and little with any concideration for video. i luv that efficient lighting, just dont like it to try and video with.

if your saying we should be Buying light for doing all the lighting of the entire set , with a "CRI" index number things, we should indeed. If we want an expanded CRI in EFFICIENT lighting it will be little spikes in the colors the chart is supposed to show correct :-)

If we want the full total spectum, then we still need the energy to output that full total spectrum from something?

Let's Stir Things Up A Bit
 

When I started this thread I thought it would go in a different direction but the comments have been very interesting. I'm thinking it may be time to throw out a statement that may stir up some reactions.

Really now, aren't all these claims that CRI is outdated and not important for consideration in selecting an LED device for video lighting just the skewed ramblings of LED light manufacturers that can't get their products to perform very well and still make a bundle selling them. Surely it must be possible to make a good LED video light without all the colour issues at a fair price. I have seen LED lights offered for $75 and for $7500....there must be a way to bring the price and quality paradigms closer together, afterall a high power top-of-the-line 80+ CRI LED like a Lumiled Rebel only costs $6 in its raw form. MAybe it's time for some of the big LED boys to fall off 5mm LED and look at the new breed of high power LEDs.

indeed there is a lot of "white" LED stuff that "can" light for video, depending on how important All the colors and all aspects of the colors are.
There are white leds with higher CRI things, if you want to do the "chart" thing :-) Nitchita is one i am thinking of (5mm).
but yes if were to get real, they tossed in some 1W china blue leds into a box tossed in a amber flip filter on the front, and are selling them for a tidy profit, and they arent very professional. but high powered led is not cheap, even UGLY high powered led is not cheap, cooling and drivers and all.

are the CRI Claims even REAL at all? Hype, do manufatures Hype and BS people to sell them things. naw never happens. Ex: 100,000hr phosphor based 5mm leds dont last 9000hr to 50%, First complete fraud lie. Overdriven or overheated in some consumer items they are sold in they are at 50% in less than 300hr. (not the same for non-phosphor based, or "high-powered")

All the high powered leds still suffer from reduced spectrum, even if they can light a CRI chart, most of them you can see it with the lowest form of color chart the camera being aimed at. Rebel LED with CRI? only one i know that could do even a good CRI is the RGB array, and it isnt $6?

They have RGB leds, and RGB combined lighting for stage and screen and all, its very expencive. but they arent efficent. if i put arrays of rebel RGB on my On-Cam light it will take more than the 20-25W they give me on the cam (for example)

i would like to know exactally what happens to the picture if i output 3 SPIKES of red green and blue , into 3 seperate filtered photon collection units 3CCD 3CMOS kinda thing? even if its not efficent or cheap.

Chris,From a manufacturers perspective, When it comes to CRI and Leds, I believe that a certain portion may be as you say "spin" from the LED manufacturers, but certainly there is also some truth to the theory that standards change and become outdated, and need revision. Untill I did research myself into CRI, I did not realise that this was NOT a be all and end all standard, Rather something constructed to serve a purpose as best it could at the time.

As far as fair pricing goes, there are many ways of looking at the factors that make a price "fair" including- build quality and reliability, efficiency of the LED's used, Quality of the Led's used and whether they've been implemented to get the maximum specified life or are being overdriven for short term gains (output), and what support and backup you get if there is a problem with your light, spectral quality, lensing if any, and light properties such as homogenity and even colour distribution.

That said there is a simple way of looking at apparent value, but it only takes ONE of these factors into account.
That is to look at $ per watt, How much do you spend per watt of light you get.

For Example,

Litepanels using their 5mm leds - approx $ 1800 for 45watts (1800/40) = $40 per Watt.

Cool Lights USA 5mm Leds - Approx $529 for 48 watts (529/48) = $11 per Watt

KometLed 12 - using 12 x 18 watt Leds, approx $6400 for 216 watts (not including PSU consumption) (6400/216) = $ 29 per Watt

Outsight Creamsource using 84 high power Luxeon Leds, Approx $7000 for 400 Watts ($7000/400) = $17.5 per Watt

(all pricess approximated in USD.)

This is a very rough comparison, as it obviously does not take into any of the abovementioned factors, nor does it have any way of measuring the EFFICIENCY of the LEDS Used, which is a Major factor relating to consumption of power vs output.
(also,all of these kits have very different accesories, just for further confusion.. )

Sure, Its true that you can buy a Rebel LED for as little as $6 or $8, but this takes into account nothing for the drive circuitry needed to regulate current, the PCB needed for mounting the LEDs, the Heat management system, lensing, DC supply, mounting and rigging, connectors, cabling, or design.

Unfortuntely I think that the lack of standardisation will continue in this area for quite some time, but all we can do as a manufacturer is try to supply the highest quality information about our products so that people can make the best choices for themselves and their needs at that point in time.

Marty, Yes this is a terible thing that some manufacturers are doing, but unfortunately it is partially due to their own ignorance of the properties of LED and drive currents/ heatsinking as well as using the wrong leds for the job also.
Im not condoning it. Im just acknowledging that it is a sad situation. Many manufacturers have jumped onto the LED bandwagon without understanding the technology, and unfortunately this hurts the consumer as much as it does the LED industry.

As with any new technology, especially at the beginning, there will be large extremes between the ends of the market, some manufacturers get the price/quality point right, and others do not.

Good luck to you all in your search for the right LED's for your situation ! there are many good ones out there for different applications/ expectations.

T

Isn't the rating of wattage/$ somewhat of a less than ideal standard by which to metric the performance of an LED lighting device. Many manufacturers also list light performance using a lumen reference--completly not appropriate for evaluating lighting device performance. The only way to really evaluate the light output (not quality) is via a Lux or Foot Candle reading at a given distance from the fixture. What matters in terms of brightness is the amount of light falling on our subject. Of course the evenness and falloff characteristics are another matter, some lights are way bright in their central sweet spot but fall off so quickly that they're only good for the "deer in the headlights" look:)

So really what we are saying over a few of these posts is that a method of metricing LED lighting devices light output for video purposes is a somewhat ellusive science. To do the job right we have to consider all of the following--and in some cases if one component is poor it impacts the other considerations so greatly that the entire fixture should be written off:

1. Colour rendering quality, now is that as seen by the eye or the sensor?
2. Light intensity, and the homogenous nature of its pattern
3. Colour temperature, for consistancy and matching with other light sources
4. Full spectrum output, free of peaks and valleys

What else did I miss?

And another thing, why hasn't anybody mentioned the fact that LED lights currently seem to be a disaster at single shadow rendering. It's probably not possible to deal with this as long as the fixtures keep using hundreds of LEDs.

Or is single shadow rendering just a bunch of bull put out by the hard light manufacturers to put people of the LED revolution? Comments?

Too right.. We've just built a tool to start showing the test values of some of these metrics- both of our own lights, and those made by traditional lamp manufacturers plus other LED Manufacturers.. It really is a work in progress, but with only three lights up, you can already see where the idea is heading.. Im thinking of something that very simply allows you to profile or compare several lights to each other quickly.

We've started by only showing power output (lux/ft-candles/f-stop) but im keen to add other metrics also, to help give a better overall picture of what a light might do..
(one of the next simple things to add is watts consumed / efficiency)
If anyone wants to have a play and give some feedback that would be very helpful !

the "Compare" tool is at Outsight
Its very newly up, if you break it, let me know how and we will get it fixed !

Chris, I really like your list of consideration metrics.. I wonder if somehow we can all come up with a way of scoring each, then translating that into an overall score for a light, an overall metric. (obviously you would want to show it's makeup also, how you arrive at that number when presenting it for it to be REALLY useful)

I have added a couple of metrics that I think may be helpful - and rearranged a little

1. Colour rendering quality, now is that as seen by the eye or the sensor?
2. Light intensity, and the homogenous nature of its pattern
3. Colour temperature, for consistancy and matching with other light sources
4. Full spectrum output, free of peaks and valleys
5. Colour homogenity with other units from the same product line (Taken from X individual pairings)
6. Lumens per watt total efficiency (how much light do you actually recieve at the target for a cost of x watts)
7. Homogenity of the beam (how even the distribution of light is)

So if you added all of these 6 up, say like this :

1. gets 20% (colour rendering, to a chip, film, or eye. )
2. gets 20% (output power is important, right ? )
3. gets 10% (CCT should be within range of tungsten or daylight.)
4. gets 10% ( my weighting would suggest color rendering more important than spectrum coverage)
5. gets 10% (colour homogenity is also a slightly less important metric but still something to be aware of..)
6. gets 20% (efficiency )
7. gets 10% (homogenity)

Thats a very rough hack at the idea...

My question now is : How far can we push this ? Are there enough people interested in the truth about their LED's to get in to scorings of this sort ? Seems like it might be worth the work for us all. :)

Now we're cookin'
What does everybody else think is important for LED to rule the roost of location and studio lighting.

I doubt my mention of doing some work could have scared everyone away from the thread,
I thought we were all chomping at the bit to solve some stuff, sorry if I seem overly enthusiastic !

Any further thoughts anyone ?? :)

T

I think the majority of DVInfo members are simply after "a light".
Once you get into the more indepth considerations you're outside the orbit of the one man operation because of cost and portability. This is what's making LED lighting popular, one can buy an affordable, convenient light. The quality of the light it provides might not be perfect but it's better than no light. Once you get beyond the $500/light pricepoint the landscape changes and the size of the market decreases.
For studio lighting the majority have already moved away from tungsten, at least down here. This is a conservative market, lights last a long time and the current fluro and HMIs work well. For LEDs to gain market share they need to offer something dramatically better or a new feature. So far I see the ability to change color without gells as being the strongest selling point.
Sorry if this is way off the original topic, more addressing the issue of why this isn't raising a huge amount of interest.

Tama, Oh yeah I'm in, just been shooting 24/7 for the past week. The show wraps tomorrow night so I'll be returning to the forums over the weekend. Been pondering a game plan, let's see if anyone cares. I agree that many just want a fairly priced light that works but if you look at the hundereds of posters over at the candlepower forums CRI is a hot topic. Probably not an area of interest for many but some inquiring minds surely need to know.

Cheers 'til then

In the mean time someone care to enlighten me on the difference between a spectrophotograph and a spectroradiograph?