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Color and Light · entry 42 of 52
Fluorescent materials absorb invisible ultraviolet light and re-emit it as visible color.
The longer version
A fluorescent molecule absorbs a high-energy photon, loses a little energy as heat, then emits a lower-energy photon of visible light. Because the emitted photon has less energy than the absorbed one, the emitted colour is always shifted toward the longer-wavelength end.
This shift is called Stokes shift, after the nineteenth-century physicist who described it. The conversion is nearly instantaneous, so fluorescence stops the moment the ultraviolet source is removed, unlike phosphorescence. Laundry brighteners, highlighter ink, and banknote security features all depend on the same conversion, which is why they look different under a black light.
Where this entry sits
These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.
More From Color and Light
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Read 44Polarized sunglasses reduce glare by blocking light waves vibrating in one particular direction.
Read 45Soap bubbles show shifting colors because thin films interfere with reflected light waves.
Read 46Oil on wet pavement shows a rainbow pattern for the same reason thin soap films do.
Read 47A peacock feather gets iridescent color from microscopic structures rather than from pigment.
Read 48Butterfly wings often shimmer with structural color produced by tiny scales instead of dyes.
Read 49Blue pigments are rare in nature, so most blue animals rely on structure instead.
Read 50Cameras capture color by filtering light through red, green, and blue sensors.
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