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Spectral distribution of LED softlights?


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#1 Karel Bata

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Posted 02 April 2009 - 03:09 PM

In my wanderings I found this page http://ledmuseum.hom....net/ledwht.htm about the white LEDs available. What strikes me is how uneven the spectral distribution is. Far better than most other LEDs, but still pretty bad.

Does anyone know if the LED softlights currently available from hire companies use some proprietary LED? Or are they just as bad as those listed? :(
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#2 John Brawley

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Posted 03 April 2009 - 12:13 AM

In my wanderings I found this page http://ledmuseum.hom....net/ledwht.htm about the white LEDs available. What strikes me is how uneven the spectral distribution is. Far better than most other LEDs, but still pretty bad.

Does anyone know if the LED softlights currently available from hire companies use some proprietary LED? Or are they just as bad as those listed? :(


LED's are inherently very monochromatic so i don't think we'll see LED's matching the evenness of tungsten or the sun. Several years ago i started building lights out of combinations of LED's and some are starting to do this now. But even mixing RGB and more you still tend to get spikes (or dips really)

They are getting pretty close to fluros and people seem happy using them for a lot of film and TV work.

jb
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#3 Keith Walters

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Posted 03 April 2009 - 12:38 AM

In my wanderings I found this page http://ledmuseum.hom....net/ledwht.htm about the white LEDs available. What strikes me is how uneven the spectral distribution is. Far better than most other LEDs, but still pretty bad.

Does anyone know if the LED softlights currently available from hire companies use some proprietary LED? Or are they just as bad as those listed? :(

White LEDs are actually blue LEDs with a synthetic Garnet crystal added that fluoresces yellow under blue light. The mixture of yellow and blue gives a reasonable approximation of white, but the yellow light tends to have a deficiency toward the green end, while the blue component is basically a monochromatic spike.

So basically a white LED works on a similar principle to fluorescent lights, except fluorescents produce ultraviolet light and use white fluorescing powder.
White LEDs have been made which use ultraviolet LEDs and similar white fluorescing material, but the highly concentrated nature of the UV light produced tends to rapidly degrade both the fluorescent material and the plastic moulding of the LED. True UV LEDs are also very expensive.

The actual colour of white LEDs available varies considerably, so I would imagine that the manufacturers of the LED softlights probably do some sort of pre-assembly matching.

By the way, white LED Xmas light strings can be used to make excellent softlights. Generally, the LEDs are rated at about 20 milliamps, but most light strings only run them at a tiny fraction of this. With all the LEDs drawing about 20mA each, typical 300 LED light assemblies can be made to safely draw something between 2 and 6 Amps, depending how the string is wired. You may need some technical help to do this, but the results can be well worthwhile.
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#4 John Brawley

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Posted 03 April 2009 - 12:42 AM

By the way, white LED Xmas light strings can be used to make excellent softlights. Generally, the LEDs are rated at about 20 milliamps, but most light strings only run them at a tiny fraction of this. With all the LEDs drawing about 20mA each, typical 300 LED light assemblies can be made to safely draw something between 2 and 6 Amps, depending how the string is wired. You may need some technical help to do this, but the results can be well worthwhile.


And a DC PW power supply too.....

jb
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#5 Karel Bata

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Posted 03 April 2009 - 05:21 AM

Cheers guys! :D

You might be interested to know that Justin Lovell makes budget softlights http://www.framedisc...8mmspecials.htm from stuff supplied by Luminous film $80 for a 6x6 unit. Maybe next time I'm in Toronto I'll get one. I was curious as to how white these things actually were.

Anyone considering making one of these themselves should check out the candlepower forum. There's guys there who know more about making budget light sources than can be considered really healthy. Power supplies and heat sinks are major topics. You can also vote for your favorite flashlight!

And as always Keith you are a walking encyclopedia! :D
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