Ms. Munir SNC2D

There are many sources of light: Sun Incandescence Electric discharge

Electric discharge tube with electrode at each end. The tube contains a gas [neon, argon, …] The inside of tube is lined with phosphorus. When electrical energy excites the gas electrons, an invisible UV light is emitted which is absorbed by the phosphorus emitting visible light.

The emission of light by a material or an object that has not been heated is called luminescence. –Phosphorescence: light emitted due to exposure of source to UV and that continues to emit light for some time even in absence of UV afterwards (glow-in-the-dark objects). –Chemiluminescence: light produced by mixing of 2 chemicals (glow sticks). –Bioluminescence: light produced by chemical reactions in living organisms (jelly fish).

Light behaves like a wave, called an electromagnetic wave. The distance from one crest (or trough) of a wave to the next is called a wavelength.

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