[elliottb]

I believe it was Adam Blundell that was doing some experimentation with natural sunlight. Natural sunlight has a Kelvin rating of right aroung 6700k (give or take). Most people do not like the look of the yellow in the tank so the supplement actinics and higher degrees kelvin (10000k-20000k). Adam suggested he could put some colored tints on a window which would allows light to pass through but only certain kelvin. So depending on how tinted the window would be, that would be the kelvin of the light.

I personally thought this was a brillient idea.