of our five senses, sight is perhaps most used by humans in interpreting information from our surroundings, with a significant portion of the brain's cerebral cortex devoted to processing signals from our eyes. we tend to think of light as being emitted from incandescent, high-temperature sources, e.g. the sun, a light bulb filament, or burning fuel. yet there is a form of light, luminescence, which has its origin in low-temperature sources. some forms of luminescence are familiar to us, others not so much. for instance --
bioluminescence is light from living organisms, produced chemically. fireflies, glowworms, and oceanic plankton are familiar sources. it is a specialized form of chemiluminescence.
chemiluminescense is the emission of light as the result of a chemical reaction. examples: lab analysis of organic and inorganic substances, illuminated watch dials, and spatial lighting or safety lighting (glowsticks).
photoluminescence occurs when a substance absorbs, and then re-radiates, electromagnetic radiation. applications include highly reflective safety clothing and signs.
sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound.
and so on. now you know.