Originally Posted by
Looigi
You're not turning the light red. You're only letting the red out and blocking the other wavelengths, so the net amount of light is much less than what you get when it's white, and the power going into generating those other wavelengths is wasted. A red LED emits only red light. All the power is consumed in generating the red light. (there is waste heat in both cases, of course).
That might be true if the 'filter' was 100% effecient. It isn't and lots of white light still gets through resulting in a slightly washed out 'red ' light thats still extremely bright. I've put red lenses from Action LED on 10W white headlights with exactly that effect myself.