Low Pressure Sodium Lamps
Low Pressure Sodium Lamp Glassware
- Outer jacket is hard glass internally coated with a thin film of indium oxide
- Discharge tube is 2 ply, sodium resistant, borate glass
Cap Type - BY22d (BC cap)
Gas Filling - Space between outer jacket and discharge tube is evacuated and gettered to produce a very high vacuum. The arc tube is filled with neon / argon at low pressure.
Filaments - Triple wound electrodes for long life
Starting and Operation
Starting Method - High voltage from an auto leak transformer initially starts a discharge in the neon / argon mixture. The resultant heat from this begins to vaporise the sodium and discharge slowly transfers across to a sodium base.
Operation - Once the sodium arc is established, the neon / argon gas becomes a buffer to retain electrons int he arc stream. Stability is reached when the arc tube reaches 230oC (normally 8-12 minutes). The sodium is still at low pressure and will restart when hot.
Restrike - Instant (but depends on control gear circuit).
Operating Position - Base up ± 110o (up to 55w) Horizontal ± 20o (90w and over)
-20oC minimum starting temperature
Colour - Yellow / orange
Correlated Colour Temperature = 1800oK
Chromaticity co-ordinates - x = 0.570, y=0.430
Efficacy - Up to 182 lm / w
Source : Crompton Lamps