Portable studio light

[sisto]

I want to make a small and portable light for studio photo and video recording. I was thinking about using 3 AA NiMH batteries in series.
Maybe I can power up to 2 or 3 leds?I'm not sure how many I can power with 3 AAs.
Also the leds would be connected in parallel.

Here's a diagram of my idea, an image is worth a thousand words.
http://img135.imageshack.us/my.php?image=text4696lg2.png
Thanks for reading!

 

[bbgobie]

Ive been thinking of a similar project.
Several concerns are the amount of light.
And the quality of light. Would need a daylight CCT with high CRI and a system capable of delivering very constant results.

I will be looking into this further after I finish my bike light project

 

[qwertyydude]

I've been tinkering with an idea of a dimmable studio light for video. It uses 21 SSC P7 led's driven at max using a solid copper heatsink base with fan cooling. Should be about 15,000 lumen. I guess if you don't need the dimmability you can use a simple HID setup. But if you want AA powered you'd at most be able to drive 1 P7 which should be plenty for just close up video work. And brighter than generic 3w leds or even 3 fully driven crees.

 

[TigerhawkT3]

First, read about the disadvantages of parallel LEDs here.

Next, read about video lights I've made here.

qwertydude, what power source and driver will you use for your project? (21 P7s at more than $20 each would be over $400... ouch. )

 

[sisto]

TigerhawkT3, Thanks for the tips. I think your first link points to this same thread. :thinking:
BTW, those are some very nice studio lights you have there!

 

[snarfer]

It uses 21 SSC P7

SSC P7 has CRI 70. Pretty awful for professional photographic applications, although might be OK for home video and ENG. I think CRI about 88 is really the absolute minimum needed, but most professional lighting is 92+.

There are other LEDs out there more appropriate for such use. Nichia 083 for example.

 

[TigerhawkT3]

Whoops, sorry about the link - copied this thread's link to get the right format, then forgot to change the thread ID.

snarfer, two words: white balance. Any decent camera will have no problem with light from blue>phosphor LEDs.

 

[bbgobie]

Whoops, sorry about the link - copied this thread's link to get the right format, then forgot to change the thread ID.

snarfer, two words: white balance. Any decent camera will have no problem with light from blue>phosphor LEDs.

WB is not related to CRI at all.
To have cheap crap lighting is no problem.
To have excellent light is difficult.

 

[TigerhawkT3]

WB is not related to CRI at all.
To have cheap crap lighting is no problem.
To have excellent light is difficult.

Yes, they are related. If a light like a white LED is slightly deficient in red, giving it a lower CRI rating, white balance will make the camera boost the red in relation to blue and green. Cameras only care about the ratios between red, blue, and green. As long as you don't have a royal blue or a violet light source, a decent camera should be able to white balance a slightly off-white source into what looks like neutral white.

 

[snarfer]

Yes, they are related. If a light like a white LED is slightly deficient in red, giving it a lower CRI rating, white balance will make the camera boost the red in relation to blue and green. Cameras only care about the ratios between red, blue, and green. As long as you don't have a royal blue or a violet light source, a decent camera should be able to white balance a slightly off-white source into what looks like neutral white.

Like I said, that may be OK for home video or ENG, but not for studio lighting:

(1) If you boost the red by using white balance on your video camera you introduce lots of grain into the red channel.

(2) There's a discontinuous spectrum problem too. Some wavelengths are completely absent from the output of the light, therefore you can boost all you want but they're not coming back.

(3) You assume that the LED light is the only light. If there are other light sources and you change white balance, well then you won't get a consistent color unless you gel the other light sources to match, which might be difficult if the other light source is, for example, the sun, or the sun reflecting off some large surface.

(4) Gel the LED all you want, you can't fill in the gaps in the spectrum.

(5) Add some red and cyan/green LEDs to balance things out and now you see the weird extra colors whenever the light reflects on any shiny surface or makes a hard shadow. So you diffuse it to get rid of that, well now you can't use it undiffused and you lost a lot of output.

(6) There are other cameras besides video cameras out there. Some of them still even use actual emulsion. And those don't have white balance when I last checked.

(7) Do you really want to have a $300 an hour plus color correction process dealing with issues like this?

(8) The P7 wasn't designed for this application. So why use it when there are more appropriate alternatives available? If you're spending hundreds or thousands of dollars on LEDs is it that hard to pick up the phone and call a manufacturer in order to place an order?

 

[TigerhawkT3]

1-2, 4: AFAIK, today's power LEDs just have some slight deficiencies in red and cyan. If large sections were completely absent, it wouldn't look white to us. In my experience, it hasn't been much of a problem.

3: Also in my experience, we've gone with (my) LED lights because there were no other available sources. It'd take a monster light to compete with the sun, while the OP mentioned a "small, portable light."

5: Yep.

6: Like I said, you just need "a decent camera." (Just kidding! :nana: )

7: I haven't had this issue. In my first video production project, I didn't use LED lights, but some of the scenes that I must not have WBed properly had a greenish cast from overhead fluorescents (footage at an indoor shooting range). Took about five minutes to fix in Avid. :shrug:

8: I think we might have different applications in mind. Portable, small, efficient, easy to use, and hopefully inexpensive has been my general goal with video lights. It's only in my most recent one that I've decided to go with mains power as opposed to batteries. It sounds like you have much bigger goals in mind.

I like using LED lights because they work for me. If you don't like 'em, don't use 'em. Different strokes for different folks.

 

[snarfer]

I didn't meant to disparage use of LED lights for video. I manufacture an LED light for professional film/video applications myself.

I was referring to the poster who stated that he was planning to make a studio light with a large array of P7s, not the OP.

I just wanted to point out that there are many other white LEDs to use besides a P7, a great many of which would produce a more useful quality of light, at no additional cost. It might not make such a difference for your average video shooter. But to someone shooting on Red, for example, it would be important.

Of course, yes, the applications I have in mind, professional feature film production and television commercial production shot primarily on 35mm film, is probably not what the OP had in mind. But that doesn't mean we should throw the idea of color rendition out the window.

 

[blasterman]

Having worked in high end photo reproduction for years I'll be the first to promote high CRI light sources for video recording and especially display (the later is actually more critical). White LEDs behave a lot like 'full spectrum' or 'daylight' CFLs in terms of color reproduction because of their spikey spectrum. The result is a lack of color fidelity with specific, high saturation colors (dense reds, off blues/grees, etc.,) and poor rendition of continuous colors. Skin tones often look bland and lack depth.

However, this can be 'helped' by the simple approach of cranking up the saturation in post production and let the colors lay as they may. This might blow out some colors, but gets you in the ball park with other colors. If it's not that critical, this approach is viable.

It'd take a monster light to compete with the sun

Again, Solux Halogen bulbs do this at 50watts / 12-14 Volts with no problem, but 50watts isn't practical for small batteries.

 

[bbgobie]

I did some preliminary calculations last night.
AB800 are rated at 14000 Lumens / second. 90% of this light comes within 1/2000 second.

So really you have about 28 000 000 Lumens for 1/2000 second.

If you don't mind longer flash duration ie 1/1000 you could do 14 000 000 Lumens for 1/1000 to get the equivalent exposure.

Assuming you care about CRI, you could burst a Nichia 083 at about 150 lumens, so 93 333 Nichias required.

If you dont care about CRI, you could probably burst an MCE for 1000 Lumens, or 14 000 MCEs required.

If those #s are correct than in no way will I turn this into a studio light project. When my hand heals, I will do some testing with the MCEs I have on hand with my SLR, but do not think current LEDs are well suited to this application.

The #s work out about the same for th AB400 if your thinking less light. The duration for them is about 1/2 the AB800, and double the brightness.

 

[snarfer]

Whoah. Those are some big numbers. I don't think that making a portable flash unit for professional use is really something you can do very well with current LED technology. At least if you are going to try for 1/1000 exposure.

On the other hand, I know a few serious studio photographers doing celebratory portraits and that kind of stuff who like to use constant lighting. Typically they're using Kinoflos or similar. But it is totally possible to make an LED continuous lighting system with superior output and color characteristics.

Using continuous lighting offers some advantage because it really is what you see is what you get. Of course it might not be your photographic style to have the additional blur of a longer shutter.

 

[bbgobie]

I'm not 100% sure on my numbers, but reading the def of lumenseconds, that is how I understand it.

Personally, hot lights are not what I'm after, so if my quick tests show the #s may be anywhere near correct the project would end there for me.

However for others, LEDs can be viable. If you have a small light tent for example.

I've seen them used on cheap ring flash, although probably only useful for macro work.

I've also seen arrays used as a soft diffuse light, but I think a reflector with proper lighting would be more flexible.

The thing with soft studio lighting is the weaker the light, the closer you have to be, the harder your light becomes.

For me, the allure of LED was being able to have enough light, in a cheap, long lasting system that didn't hog power, which would also mean portability, and great recycle time.

 

[blasterman]

But it is totally possible to make an LED continuous lighting system with superior output and color characteristics.

Just as close CRI-wise doing it with CFL/Fluorescent, and that technology is already on the shelf and much cheaper per lumen. Assuming the greater power requirements of course.

 

[sisto]

Based on some suggestions I changed my design a bit like this:

Bear in mind that I want it to be very lightweight and portable.
I also want it to be inexpensive. I've found the leds for 3 dollars each.
Is there anything wrong or do you think I should just go for it?
Thanks!

 

[qwertyydude]

To help with color deficiency you can always use a few gel filters to warm things up. But I think the whole purpose of portable light is first and foremost portability. I understand there may be higher cri leds but if you need to get 15000 lumens you would need to get insanely expensive like those led panels for like several thousand dollars. I don't even think they offer something that bright and if they did the power requirements would be insane that you might as well get several hid headlights but you lose dimmability. CRI again isn't everything, again as everyone knows color temp means something too a 100 cri 2700 k bulb would look like crap and I've taken video with my P7 led and with just a white balance adjustment everything looked fine definitely better lit than a 20 watt video light because that was too dim. All I'm saying is there is no other affordable dimmable yet very bright video lighting product, $600-700 for 15000 lumens of decently white dimmable and portable light is cheap.

 

[sisto]

To help with color deficiency you can always use a few gel filters to warm things up. But I think the whole purpose of portable light is first and foremost portability. I understand there may be higher cri leds but if you need to get 15000 lumens you would need to get insanely expensive like those led panels for like several thousand dollars. I don't even think they offer something that bright and if they did the power requirements would be insane that you might as well get several hid headlights but you lose dimmability. CRI again isn't everything, again as everyone knows color temp means something too a 100 cri 2700 k bulb would look like crap and I've taken video with my P7 led and with just a white balance adjustment everything looked fine definitely better lit than a 20 watt video light because that was too dim. All I'm saying is there is no other affordable dimmable yet very bright video lighting product, $600-700 for 15000 lumens of decently white dimmable and portable light is cheap.

Thanks! I don't really need professional quality because I only have a Casio Exilim digital camera. It's just a plain digital camera. Not an SLR like the Canon Digital Rebel but it does have shutter speed and f-stop adjustments.

I think I'll mostly use this for macro photography at home. Maybe some short clips also. I was thinking about spending 10 or 20 dollars total.

My question was aimed more at finding out whether my circuit is correct and efficient and won't drain my batteries too fast. I'm very new at using high power leds.