New Lamp for Street Lighting

Abstract

A VERY interesting new type of lamp, called the Osira, has been developed in the G.E.C. Research Laboratories at Wembley. It is intended for use in lighting stretches of arterial and country roads where the illumination required is not high and so the lack of good colour discrimination is of little importance. Blues, greens and yellows appear as in daylight, but red colours appear brownish. The lamp takes 400 watts and has an efficiency more than double that of a corresponding gas-filled tungsten lamp taking the same power. In the G.E.C. Journal for November, Mr. J. W. Ryde gives a technical description of the lamp. It consists of two cylindrical bulbs one inside the other. The inner bulb contains rarefied gases at low pressure and a trace of mercury. The space between the bulbs is vacuous. The electric discharge takes place between electrodes sealed in each end of the inner bulb. The electrodes consist of small sticks of alkaline earth oxides which have been heated to a high temperature during the process of manufacture. This is done by passing a current through spirals of wire surrounding the electrodes. They are then connected with an ordinary screw cap holder. When the voltage is applied, a discharge takes place through the rarefied gases in the volume of the inner bulb. As this bulb warms up, the mercury is volatilised. The discharge then begins to contract and finally takes the form of a narrow column, six inches long, extending between the electrodes. The electrically excited atoms in this column emit a brilliant light and are the counterpart of the filament in the glow lamp.