1. Low-temperature emission of lambency produced especially by physiological processes (as in the firefly), by chemical action, by friction, or by electrical action: As children, Jim and Kate were mystified by the little luminescences they saw moving around in the garden when it was dark; then their parents explained that the luminescence was caused by fireflies.
2. Any radiation of glimmer from a body produced by some means other than heat: Carol noticed that when she rubbed the fur of her cat on a dry evening, she could hear a crackle and see some luminescence in the form of sparks.
3. Any emission of effulgence at temperatures below that required for incandescence: Sharon is satisfied with the luminescence in her kitchen that is provided by her fluorescent light bulbs.