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Re: 6500k vs 10,000k

>Alan asked about using 10,000K metal halide versus 6500K. 
>I had a 10,000K bulb over a planted tank then switched to a 6500K.  The
>plants did MUCH better under the 6500K.  The 10,000K bulb replicates the
>light found under several meters of sea water which is much more blue than
>that of the typical freshwater aquatic plant habitat.  To the plants, the
>effect must be that of a heavy flood - a condition they can survive in
>temporarily, but not one that they are built to thrive in.  IMHO
>I guess this just proves that K degrees, being an average, doesn´t say much about the light quality. Like if you have a bulb giving 50% sunset (3100 K) and 50% clear blue sky ( 12000K) you have 7550 K, which should be "overcast sky", but it doesn´t look like that.
>Oleole.t at larsen_dk

Color temperature of a light source can be loosely defined as the temperature 
of a black body that generates light that is perceived by our eyes as being 
the same light as the source of interest. Light sources can use different
tricks to look like having a given color temperature. They can emulate as
close as they can a true, continuous, black body spectral distribution. Or
they can fool our eyes by emiting in just a few wavelengths carefuly
chosen and balanced to give the impression of the desired color temperature.

Black bodies by definition produce a spectrum described by the Planck 
function. The sum of two Planck functions is *not* a Planck function. Thus,
no matter what mechanism the light sources use to create a given color
temperature, if one pairs a 3100 K light source with a 12,000 K source, the 
result will not necessarily be 7550 K. It can be anything, depending on what 
mechanism the two original sources use to make our eye believe they have 
the stated color temperatures.

-Ivo Busko
 Baltimore, MD