Worlds of David Darling
Encyclopedia of Science
Home > Encyclopedia of Science

discharge tube

mercury discharge tube
Mercury discharge tube

How a discharge tube works
A discharge tube contains a gas at low pressure through which electricity is passed [A]. Electrons (negative particles) and ions (positive particles) move towards the electrodes [B]. Ions strike electrodes to produce more electrons [C]. Light is produced as electrons collide with gas atoms [D].
A glass envelope containing gas at low pressure, which gives light due to the collision of electrons with gas molecules. Discharge lamps, filled with one or more of various gases, are used to give colored light: mercury vapor gives purple, sodium vapor gives yellow, and neon gives red. Early discharge tubes, called Geissler tubes, were used as toys. A fluorescent lamp is a discharge tube coated internally with a fluorescent substance.

Related categories