Re: [OM] LEDs R Us

[Mike Gordon via olympus]

CN writes:

> I received an email today advertising LED lights for photography.  The 
> temperature was supposedly adjustable from about 3,000 to 5,500 K.  It sounds 
> interesting but I know nothing about how good it really is or if the light 
> has decided temperature spikes.

I went digging a bit after Paul's comment.

I have some of the earlier Cree ones in our bathroom and all I can say though 
the lights look white and on the warm side, skin tones are rendered somewhere
on the spectrum between sallow and jaundiced.   The human eye is especially 
good at detecting problems with skin tones. Found data on the the spectral 
power distribution (SPD) and it appears I have ones prior to the use of the 
"notch" filter to cut down on the yellow and raise the R9---another imp't 
factor.  Suspect they still all use blue  LED covered by a yellowish phosphor 
coating usually made of cerium doped yttrium aluminium garnet (YAG:Ce) crystals 
and then add a filter.  

http://www.designingwithleds.com/measuring-light-quality-philips-cree-led-bulbs-spectrometer/

The GE reveal ones may be slightly better for proper color rendition  
sacrificing efficiency/cost/lifespan. 

http://www.cnet.com/news/shining-a-light-on-high-cri-led-bulbs/

I don't know how the ones dedicated for video/photog are constructed but 
suspect they have the same issues.  They can be fixed apparently but takes some 
PP work.  I believe the near UV LED's with fancy phosphors have superb  color 
rendering with the white point determined by the phosphors only---would not be 
easily  tunable for color temp  however. 


Still a tad off-color, Mike
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