Page 38 - Curriculum Visions Dynamic Book

Sodium light
When sodium is heated it burns with a brilliant orange flame. This property can be seen in almost every city in the world, where it is used to provide the bright orange illumination for city streets.
Discharge tubes
The way sodium is used for lighting is
not unlike the way light is produced in a fluorescent tube in your home. The tube contains a gas at a high pressure. In the case of sodium it is called sodium vapour.
At both ends of the tube are electrodes, pieces of metal that can introduce electricity inside the tube.
When a very high voltage is applied
to the tube, the vapour begins to glow.
High pressure sodium vapour lamps give out a brilliant yellow–orange glow.
Living with yellow–orange light
The light produced by a sodium lamp is of one colour. This is quite unlike the light produced by the Sun, which contains many colours mixed together to produce white light.
Yellow–orange light makes many objects look dull and flat. To make the light more acceptable, some sodium vapour tubes have a
coating of a fluorescent material (just like fluorescent tubes at home). This changes the orange light to a slightly whiter light.
 A piece of sodium being heated
in a Bunsen burner flame shows the characteristic yellow–orange light of sodium.
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