Spectrum, LED vs fluorescent

May 8, 2008

If you ever wondered why things look “wrong” under fluorescent light, this is why.
Carpooling to Vermont with a physicist, he explained what I had already once seen with my own eyes, which is that fluorescent lights dump all their energy into a handful of colors. Not around a handful of colors, but exactly on a handful of colors. You can see this yourself with a diffraction grating (one can be found in the Klutz Exploratorium book). White LEDs, in contrast, emit a smear of colors closer to what we expect from a traditional light bulb (but with much less infrared, also known as “heat”).

Compare these two lights. The first is a halogen light in a ceiling flood.
Notice how the colors (the spectrum) are a continuous smear.


The second is a compact fluorescent in a ceiling flood.
Notice how the colors appear as distinct, separated images of the flood light.
The light is only producing exactly those six or seven colors that you can see there,
and nothing in betweeen. When you illuminate something with that light, it’s no wonder
that it looks a little peculiar.

compact fluorescent

Here’s the spectrum from a (bright white, I think) LED strip light.
Notice how the colors are more or less continuous; not quite as good as the halogen,
but close:


By combining white LEDs of different color temperatures, you can get a good distribution of colors.

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