Re: [GSAS-Member] CFL bulbs

[Erik Olson <erik@thekrib.com>]

On Thu, 22 Oct 2009, clayton anderson wrote:

> Thanks Eric, so it sounds like color temp. (Kelvin) and wavelength are
> independent, if I'm hearing you correctly.

I wouldn't call them independent.  Think of a particular color temperature 
as representing a certain mixture of the different wavelengths.

Let me try to simplify in an example:

In some not-so-great fluorescent bulbs, there are only three wavelengths 
(or "spikes") in the spectrum.  red 600 nm, green 550 nm, and blue 470 nm.

One might make white light with a color tempeature of 3000K as 30% red, 
40% green and 30% blue.

But 5000K might be more like 25% red, 43% green and 32% blue.
And 8000K might be 18% red, 47% green, and the rest blue.

In reality it's a continuum, not just three spikes.  The better tubes 
(higher Color Rendition Index) smear the spectrum instead of having just 
three spikes.  But that's one reon people like sunlight, candlelight and 
incandescent bulbs -- they are all so-called "black body radiators" 
and have a nice smooth spectrum.  The color temperature literally means 
how hot the object is to produce that distribution of light.  Which means 
that light bulb filament is 3000 degrees!

http://en.wikipedia.org/wiki/Black_body

And there actually IS a direct correlation between the color temperature 
and the "peak" wavelength when dealing with the above. peak wavelength = 
b / Color Temp.

I have a few crappy drawings I did 12 years ago to illustrate some of 
this, though I like the wikipedia article better:

http://www.thekrib.com/Plants/People/Darn/darn3.html


   - ERrik
-- 
Erik Olson                                                        Sent from my 
crusty old Linux box
erik at thekrib dot com
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