Sodium Vapour Lamp
Sodium Vapour Lamp consists of a discharge tube made from a heat
resistant glass, containing a small amount of metallic sodium,
neon gas and two electrodes, Neon gas is added to start the
discharge and to develop enough heat to vaporize the sodium.
Because of law pressure inside the tube, a sufficiently long
tube required to obtain more light. To reduce the overall
dimension of the lamp, this tube is generally bent into U-shape.
The light produced by this lamp is yellowish which is produced
at its optimum pressure of about 0.004mm of mercury. This
pressure is obtained at a temperature of about 280