Shadowlands;Let there be light

22nd October 1999 at 01:00
John Stringer and Dinah Starkey explore religious festivals and the science of illumination

Light bulbs and candles are sources of light. The Moon and some super-reflecting road signs seem to be sources of light, but have no light of their own. Light and heat are almost always produced together; but some creatures produce light by bioluminescence - making use of a biological process that makes no heat. Deep-sea fish lure their victims by glowing like bait; glow-worms and fireflies sparkle to attract a mate.

Some paints glow briefly with "fluorescence"; while self-adhesive stars shine with a longer-lived "phosphorescence". They contain phosphors - chemicals that can absorb the energy from light, slowly releasing it as a light greenish glow.

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