south metropolitan gas company full range | lanterns
High pressure gas lamp. First introduced in 1935. The light from a cylindrical high pressure gas mantle must
be redirected; this redistribution could be effected by altering the shape of the mantle
itself so that a greater proportion of the luminous output was radiated in the direction
where the greatest intensity of illumination was required. This was adopted in the Supervia
lamp. Fitted with a thin flat mantle, of which the flat
surfaces were exposed in directions up and down the roadway. A candle power of 2000 c.p.
was developed in the direction along the road for a consumption of gas which with a
standard cylindrical mantle would only give 1000 c.p. The candle power was further
increased by the use of a fluted refracting dish. Originally developed as a high pressure
gas lantern but low pressure versions was then developed. Low pressure units had either one or
two flat mantles arranged in-line facing the road. By 1937, there were 1,800 Supervia lamps
lighting nearly 73 miles of road. The verical polar diagram shows the distribution of the
Supervia lamp (solid line) compared with a normal mantled non-directional high-pressure
gas lamp (dashed line). The azimuthal distribution curve is 15°
below horizontal effected by an axial dish refractor.