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I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?

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Yes, LED's, luminescence of phosphorous (CRT screens), most of the current screen technology, fluorescent lights. They aren't a thermal source. They heat up due to the electric current but that's not the working principle.

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Just wanted to add lasers that operate in the visible frequency range. – Neuneck Jul 26 '13 at 17:58
LEDs, too, produce light without much heat (i.e., the heat production is not directly tied to the light, as with black-body thermal radiation like the Sun or an incandescent bulb). – Phil Perry May 27 '14 at 18:35
@PhilPerry Yeah, that's mentioned in the answer. – user80551 May 28 '14 at 5:15

Super-continuum sources are well known non-thermal white light sources. The gist is a laser beam interacts with a specially tailored nonlinear material to generate ultra-broadband coherent light. A few references:

Supercontinuum light

Demonstration of Stimulated Supercontinuum Generation – An Optical Tipping Point

Generation of a 650 nm - 2000 nm Laser Frequency Comb based on an Erbium-Doped Fiber Laser

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Yes. A single atom can emit visible light and certainly is not a thermal source. My favorite example of non-thermal source of visible light is the Crab Nebula (remnant of supernova 1054), where light is generated by synchrotron mechanism.

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