Emu XL-7 & MP-7 User's Group

This is totally off topic, but it's something that always intrigued 
me...  Read on if you're interested in human color perception, 
otherwise, feel free to toast this one!

erik_magrini@... wrote:

> My second thought was to take blue film and lay them over the LED's 
> inside the case (Red+Blue=Purple, which would be cool too!).  Sadly, 
> this didn't work either as the RED is just too bright, 4 layers of 
> blue gel film did nothing to change the shade at all.  Oh well, it was 
> a cool idea none the less!

Unfortunately, that'd actually be Red-Blue=Red.  Starting off with a 
pure red (I think somewhere around 730nm in our case) doesn't leave any 
other colors to filter out.  This is one of the fallacies of the grade 
school teachings we all get (though try and explain spectral analysis to 
a 6 year old...)  Things that look the same color to our eyes are not 
necessarily the same color.  Our eyes are sensitive to three distinct 
colors (RGB) out of a continuous spectrum.  When you see yellow, it's 
really that you're seeing about the same amount of red and green, which 
your brain interprets as yellow.  Computer monitors don't produce yellow 
(or white, or orange, or purple, etc), they just fool your eye into 
thinking that it sees yellow.

So in the above case, your eye can't tell that it's a pure red from a 
red lamp for example which may look like the same red, but not be a pure 
color (i.e. containing a whole lot of wavelengths, just centered around 
that frequency).  That's why most gels in catalogs come with a filter 
spectrum so that you can know how it will interact with other gels.

Anyway, sorry for the rambling, I just always thought how we perceive 
things is a cool subject...

-Aaron