Low Pressure Sodium Lamps

Low Pressure Sodium Lamp Glassware

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

Physical Characteristics

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

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