The lamp is enclosed within an outer glass jacket to secure heat retention.

The discharge tube is filled with argon gas and a small and carefully measured amount of mercury.

A stabilising choke is required in series with the lamp, and it is suggested that a condenser be connected across the supply in order to correct the power factor to a reasonable degree. In the case of low supply voltages from 110V to 165V, the above mentioned choke must be replaced by a leak transformer.


Starting Characteristics
The discharge commences as a low intensity glow, but as the mercury rapidly vaporises, the discharge becomes more intense and narrows down to approximately ¼" diameter.

The normal mercury lamps take some five minutes to arrive at their full intensity.

Should a violent fluctuation of supply take place it is likely that the lamp will be extinguished and no discharge at all will be apparent until the lamp has substantially cooled to its normal starting conditions.


Advantages Claimed For Sodium Lighting

1. Efficiency. Initial efficiency 32 to 45 lumens per watt. Two and a half to three times the efficiency of tungsten filament lamps.

2. Life. The average life is 1,500 hours as aginst 1,000 hours for normal lamps.

3. Visibility. The incomplete spectrum of the mercury lamp with its yellow, green and blue lines has been found to give very sharp definition of objects in a manner which white light does not, at street lighting intensities.