www.litepanels.com

Some issues with LEDs
 

I spent a fair amount of time on the phone with one of the LED light panel manufacturers.

There are some interesting issues with using LEDs:

1. They have a very sharp demarcation between the area they light and the area outside the illuminated circle. It is a very sharp cut-off, not like an incandescent lamp with its gentle fall-off.

2. The shadow cast by the LED light falling on an object tend to be rainbow colored rather than the gray that would be cast by an incandescent lamp.

3. LED light output is highly sensitive to input voltage. For example, a LED panel rated for 12 to 14 volts input power will only deliver its rated amount of light at 14 volts. At 12 volts it is significantly less.

4. The colder the white (higher color temp), the more light a LED puts out. As they approach Cool-White color temp, the light output has gone down because the phosphor coating has to be made thicker to bring down the color temperature.

5. A white LED is generally made by using a blue LED to excite a phosphor coating to emit the white light.

6. The high-powered LEDs, the 1 watt LEDs, may not be suitable for video lighting according to my source. He said that while they are great for stop light and panel light applications, the methods used to create the apparently high output won't work with a CCD sensor. I think he means that the bright LEDs are driven with a pulsed, not a DC power and that the pulses may be detected by our cameras.

I may have one of those 198 LED panels to test in the next few weeks. I'll keep you informed.

I'm told I'll be able to get my hands on one of thise big panels this week. I'll keep you informed.

I"ve seen pictures taken with and without this lamp outdoors with a digital still camera and they look OK.

Tomorrow I'll get my hands on the unit and take some pictures with my PD150.

Great Mike, please do keep us in the loop. Thanks.

OK, played with the big panel and some other interesting lights.

The big panel does exactly what I want except:

They way they wired it, there are 3 LEDs in series and then each string of 3 is in parallel with other strings to make up the light.

This causes a problem. Each LED requires 3.8 volts to 'fire'. With 3 in series, the string requires 11.8 Volts to fire. What this means is that a 12 volt battery belt or 12 volt lead acid battery will not last long before the panel turns off. That's because battery voltage 'droops' over use. Lead Acid being worse than NiCads or LiON or NMH cells.

So, instead of my 85 watt battery belt being able to power the panel for 6 hours or so, it will only run it for about the same, or perhaps lower number of hours that the belt will run my DSR-300 before it complains of a low battery.

May have to get a 14.5 volt battery belt or use the big LiONs from my DSR-300.

At least that is what I think it means. I'm trying to find a reliable source of discharge curves for my belt.

BTW, they also have a 400 LED panel ($750) as well.

It does put out a reasonable amount of light. Exactly what I'd want for filling shadows and popping colors. The LEDs are noticably cream-colored (warm white, 3000 degrees K) compared to the cool white of the 'normal' LEDs.

I like the panel a lot.

However, it is very popular all of a sudden and they are back-ordered. Probably take 2-3 weeks to get one now.

I also saw some 40-LED lights in the lamp configuration that is used in slide projectors and NRG lights. So we plugged it into my NRG light and promptly smoked it. Don't know why since the light is not polarity sensitive. Possibly the pulsed source is what caused the problem. That light is quite reasonable for use as a fill light for video.

More later

As a quick fix, since I am leaving for a shoot in Pennsylvania next week, I've purchased 2, 7-LED Flashlights that will run for about 150 hours on 4 AA cells.

I removed the light module and inserted 2 softgels between it and the front plastic lens. This gives a nice smooth light for the distance and angle at which I'll be shooting. Since these are fill lights only, not main lights (the exhibition hall has lots of light, all from the overhead but just not good enough for good color on vertical surfaces and nooks and cranies.

Now all I have to do is machine a carrier for the lights to fit on top of the PD150. Later I'll probably mount the light module in something smaller for the camera and place the batteries somewhere else.

For use on a DSR-300, I could run both light modules off the built-in power tap on the camera.

LEDs are costing nothing, so if you like to grab you solder iron.
http://www.superbrightleds.com
and even cheaper
http://www.lsdiodes.com/5mm/

and if you do not like the idea of putting together hundreds of LEDs, try the luxeon stuff.
http://shop.dotlight.de/shop/index.p...8ac6425a642bc9

Right, except grabbing the soldering iron has its own cost too. My most limited asset is time so purchasing, where costs aren't too out of line with the components makes a lot of sense.

A 198 LED array in an enclosure is worth $198 in my estimation. 40 LEDs in a M16 (projector) bulb configuration for $58 is also.

So far the only led panel i have seen was priced almost a thousand dollar, so if you know where to purchase around 300$ , il will be happy to read some references.

For $750, you can get a 400 LED panel here
http://www.ledtronics.com/datasheets/RGB.htm
Some assembly required. $198 for the panel I like.

the 198$ panel looks good , except the dead center that is pretty bad for video use.
the litepanel.com look great but 750$ for 160 leds it is about
4$ the led, so since you can get one for half a dollar, i think it still worth to grab the iron solder.

if somebody wants to start a business, he can even buy several thousand led for probably cheaper, add a printed circuit and sell the stuff as a kit.

<<<-- Originally posted by Giroud Francois : the 198$ panel looks good , except the dead center that is pretty bad for video use.

There is no dead center. The LEDs are evenly distributed. I've had that one in my hands.


the litepanel.com look great but 750$ for 160 leds it is about
4$ the led, so since you can get one for half a dollar, i think it still worth to grab the iron solder.

There are 400 LEDs in the $750 unit.

if somebody wants to start a business, he can even buy several thousand led for probably cheaper, add a printed circuit and sell the stuff as a kit. -->>>

I doubt it but go ahead and try!

OK, flashlight adapter #1.

Go to hardware store, get an 2" L-bracket (Stanley part # 75-6371), 2 x spring-loaded broom holders (Stanley part # 75-2025)for hanging brooms on wall. These are the type witha round spring arm and a plastic pad to grip the object in their jaws. Costco 7-LED flashlights fit in very nicely.

Mount broom holders to the L-bracket (one on each side) with 2 screws. You will have to drill one hole. I used 8-32 screws to fasten the broom holders to the L-bracket

Mount L-bracket on camera shoe adapter that has 1/4-20 stud.

Flashlights are now mounted side by side above the camera without interfering with CAC-12 microphone holder on Sony PD150.

I placed two disks of diffusing material and one disk of CC filter material on backside of lens cover, clamped between LED holder and lens cover. Warm White LEDs would be nicer than these Cool White LEDs.

Works very nicely.

Interesting, the LEDs get quite hot in constant use. Burn your hand on the inside metal power connectors hot. Have to turn them off from time-to-time.

Total cost for flashlights and bracketry - About $50.

Run-time is said to be about 140 hours per each load of 4X AA Cells.

Total weight, 1 Lb., 0.7 Oz.

I'm off to Pennsylvania on Friday to try them out.

The flashlights worked OK but I want a bit more power.

I've ordered the LEDTronics MR-16 warm white, 42-LED lamp. Now I'll build a good looking enclosure for it and set up for a battery. It is real tempting to use a pair of Sony LiON cells (or one of my DSR-300 LiON cells) to power it.

A major design issue is whether to mount the battery on the camera (it could be powered directly from the DSR-300 which has a power tap) or to use a remote battery. A single gel cell should power this lamp for quite a while at its maximum power consumption of 5 watts.

Any suggestions are welcome.