# Portable studio light



## sisto (Nov 27, 2008)

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!


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## bbgobie (Nov 27, 2008)

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


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## qwertyydude (Nov 27, 2008)

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.


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## TigerhawkT3 (Nov 28, 2008)

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. )


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## sisto (Nov 28, 2008)

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!


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## snarfer (Nov 28, 2008)

> 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.


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## TigerhawkT3 (Nov 28, 2008)

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.


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## bbgobie (Nov 28, 2008)

TigerhawkT3 said:


> 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.


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## TigerhawkT3 (Nov 28, 2008)

bbgobie said:


> 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.


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## snarfer (Nov 29, 2008)

> 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?


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## TigerhawkT3 (Nov 29, 2008)

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.


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## snarfer (Nov 29, 2008)

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.


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## blasterman (Nov 30, 2008)

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.


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## bbgobie (Dec 1, 2008)

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.


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## snarfer (Dec 1, 2008)

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.


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## bbgobie (Dec 1, 2008)

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.


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## blasterman (Dec 1, 2008)

> 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.


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## sisto (Dec 3, 2008)

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!


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## qwertyydude (Dec 3, 2008)

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.


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## sisto (Dec 3, 2008)

qwertyydude said:


> 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.


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## qwertyydude (Dec 4, 2008)

Your design is valid though it will drain power quite fast, each one will draw close to one amp if directly driven, plus you may have issues with heat. But for macro work you'll probably be better served by buying or making a ring light or ring flash as it'll distribute the light more evenly.


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## sisto (Dec 4, 2008)

qwertyydude said:


> Your design is valid though it will drain power quite fast, each one will draw close to one amp if directly driven, plus you may have issues with heat. But for macro work you'll probably be better served by buying or making a ring light or ring flash as it'll distribute the light more evenly.



Thanks for your comment!
I could use a pushbutton instead of an off/on switch to use it as little as possible and keep from draining my batteries so much.
I could probably arrange the leds around the camera's lens somehow so as to form a ring light. Thanks for that idea.
It's more fun for me to do it myself than to buy it.


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## SemiMan (Dec 4, 2008)

1) To the comment made above about white balancing and CRI not being related this is absolutely true. In fact, even though an LED has valleys (not so much holes) in the spectrum, you can fairly accurately white balance it AND accurately render colors, as long as you know that the LED is the predominant light source. Since you know the relative balance of the colors being projected, you can work things in reverse. It is not perfect, but will be pretty good.

2) #1 being true, not a camera on the market I am aware of balances for LEDs so you are out of luck....

3) Hence, you should go for a real high CRI warm white which will likely balance fairly well with a tungsten lighting setting.

Semiman


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## qwertyydude (Dec 4, 2008)

There may not be a specific setting for led but led light is close enough to really cool overcast daylight to use that setting. Also my camera has 3 fluorescent light settings and 1 of them is also very very close, not to mention a manual white balance and white card auto setup. It's not even anything fancy just an Olympus SP-350.


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## carnal (Dec 4, 2008)

snarfer said:


> 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.



For sure on the High CRI idea with the Nichia. Where to get and the cost?

Is the Edistar high Cri also? It is a 50w array on a board. http://www.edison-opto.com.tw/news_detail.asp?nno=23

I'd love to play with one of these.

Brian


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## bbgobie (Dec 4, 2008)

Even though we are going away from what the OP needs, just because I dont like wrong info being posted on the net all the time, low CRI means not all colours are being produced by your light source. If a colour is not being produced, no amount of WB is going to bring it back.

WB can shift the overall hue of an image, it will not magically make a colour appear.

The best simple example I can think of is if you take a picture with a red piece of plastic in front of your camera, try and WB it. You will have an image resembling a black and white image rather than a colour photo. The reason is there wer no greens, blues etc in your image. You may have been able to shift the hue of the image, but you can't make up for the missing colours.


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## bbgobie (Dec 4, 2008)

Forgot to mention, Semiman, I like your idea. Ideally you could make a spectrographic map and use it like a filter in PS, but I dont know how you would go about doing such a thing, but it would certainly be interesting!


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## carnal (Dec 4, 2008)

bbgobie said:


> Forgot to mention, Semiman, I like your idea. Ideally you could make a spectrographic map and use it like a filter in PS, but I dont know how you would go about doing such a thing, but it would certainly be interesting!



McGizmo started this thread called "High CRI and its significance". https://www.candlepowerforums.com/threads/199054&highlight=nichia+083

Sorry if you knew about it already.

This thread will answer any question you have had about spikey narrow banded led's vs High CRI' leds. 

Somewhere near the end they talked about CS3 and 4 being able to create a custom profile. This is a very cool thread. Get out your note taking paper and pencil!

Brian

quotes and link to page:

Posted by BobQubed message 196 in thread
https://www.candlepowerforums.com/threads/199054&highlight=nichia+083&page=7

Hi Folks,

This is my 1st post. Found this interesting thread using 'The Google', as Bush would say.

My primary interest in this rapidly-evolving LED technology is as a light source for photography (advanced amateur)---mostly macro and light-painting of landscape scenes.

Thought I’d add some thoughts regarding the posts on photographic color correction that I didn’t see mentioned. For critical photo work, it is possible to create a custom profile which can be used in Photoshop (CS3 and CS4) or LightRoom using a new (free) program from Adobe (released a few months ago) called ‘DNG Profile Editor’.

To build a profile, you just photograph a ColorChecker chart (in RAW format) illuminated by the intended light source (LED, etc.). Then convert it to .dng format and open in the editor. The download and details are on Adobe’s site. You end up with a camera/light-source specific profile that can be used in PS (Camera Raw) or LightRoom to color-correct any image taken under the same illumination.

I’ve been using this method with a wide variety of light sources, incl. LED’s, incandescent and fluorescent and it works extremely well, even with low-CRI sources (as long as there is a minimum level of output at all visible wavelengths). It’s even possible to color correct scenes with multiple (mixed) illumination sources having different spectra, as long as you take a shot of the ColorChecker in the same lighting as you subject.

So far I’ve used this technique with up to 6W LED lights (TeraLUX K2 drop-in for Maglite). I have SSC, MC_E (K-bin, WC) and Cree, P7’s (C-bin) parts on order from KD-they shipped today. Should provide enough throw to light-paint a large segment of desert landscape!

Bob in OC, Calif.


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## SemiMan (Dec 4, 2008)

bbgobie said:


> Forgot to mention, Semiman, I like your idea. Ideally you could make a spectrographic map and use it like a filter in PS, but I dont know how you would go about doing such a thing, but it would certainly be interesting!



Qwertydude, while the color temp for cool-white is close to the color temp for cool LEDS, the spectrum is much different. Hence, while "white" may look right, many other colors may not.

bbgobie, I think one place where it could be done, somewhat approximately at least, is in the RAW conversion. If you have a RAW output from your camera, you can adjust the conversion from what is likely bayer matrix to RGB. 

Semiman


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## snarfer (Dec 5, 2008)

For the OP here is a very cool DIY ring light project that uses fiber optics to redirect the flash. Cheap, effective, and possibly fun to build.

Regarding color correction for LED sources. One factor that definitely needs to be taken into account is the noise factor. This is especially true when color correcting video, but applies to still photography as well. Normally one or another of the color channels will exhibit considerably more noise and artifacting than the others. Usually that's the color that was missing in your light source. So when you try to color balance, all of that artifacting and noise gets amplified even more. Sometimes applying a noise filter to just the one channel can get rid of it. Other times it is so bad that the noise filter gives it a kind of weird plastic look. 

Also I will definitely second SemiMan's point about mixing sources. It certainly is important to keep in mind that most of the time the LED will not be the only source lighting the scene. So if has a completely different color cast then things are going to get weird. Weird could be good, but maybe it's not what you're looking for. 

Finally it's worth noting that the "just gel it" approach has a downside. If you are gelling a more efficient low CRI source in order to make it into a high CRI source, then you are decreasing the output. If you are decreasing the ouput you are decreasing the efficiency. If you just reduced your 15,000 lumen source to 10,000 lumen with gel, then you might as well have started with less efficient high CRI LEDs instead, and skipped the gel.


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## qwertyydude (Dec 5, 2008)

But what about if you're using 100 CRI minimag light bulbs and use the incan camera setting? I guarantee that all the blues will look black even corrected because that's exactly what happens, 100 CRI black body radiation under 2700k is pretty much useless as there is almost no blue as in less than 10% of the light is in the blue, 3200k halogen is barely acceptable in the blue range at right around 10%

Led's are not necessarily bad with a CRI of 80 it's good enough, even on the cree site if you look at the spectrograph it may seem spikey but no part of the spectrum dips below the 20% light output. And if anyone is actually a real photography enthusiast you'd know that the standard xenon flash has a CRI of only ~85 much like the led's in fact my camera's flash bulb setting is the second best setting with only manual white card balancing beating it out. So everyone trying to beat CRI into your head is only partially right, color temperature is also important.

Still don't believe me? I was talking to the lighting director of the NBC show Life while they filming the Christmas episode in the store I work at, it's a short segment in the Paws and Claws store in the Southland Mall. They were setting their HMI flood lamps and I asked him if he considered LED lights and he said he may buy them since their CRI's were close enough to work with and he was amazed at my P7 flashlight that it could produce light that looked just like their HMI's. The high powered projection lights only had CRI's of 85 and the floating blimp flood lights they used were only 70. And when the blimp lights were on you'd swear it was daylight and it's only 70 CRI and when I took a picture with my camera it was perfect at ONLY 70 CRI! All they did was put some warming gels in front of the lights and it was more than acceptable for HD video. This is the whole reason I was even considering a massive P7 array because their CRI is just as good as professional television HMI's.

So unless you really think you're quality needs to be that much better than professional television guys and you have as much experience as their lighting director who was doing professional film and television lighting for 15+ years, you can't just make a flat across the board judgement that an 80 CRI led is no good especially because xenon flashes are only about 85 and video HMI's range from 60+. All of these lights produce a similar spiky spectrum like leds yet all are able to be used even in professional work.

Plus give the guy a break, he's only trying to light up some some macro with a point and shoot.


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## TigerhawkT3 (Dec 5, 2008)

To the OP: your revised circuit should be fine. You might want to remove one cell to get reduced output but more runtime and less heat. Remember that output will decline over time, if you're planning on exact comparison shots or something.

To the "other" discussion ( :laughing: ): when I say "white balance," I mean filling the camera's field of view with a white card/paper/etc. and hitting the WB button. I wasn't thinking about built-in presets. I've had much better luck with the former than the latter.


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