The application of electric discharge lamps to daylight signalling

The light output of high-power daylight signalling lanterns of the non-directional type for marine use depends on the light output of the source itself, since only a small gain can be obtained from any optical system without restricting the angle of beam divergence. Incandescent lamps and carbon arcs both have limitations as high-power signalling sources, but the high-pressure mercury-vapour lamp has peculiar advantages. The paper records the history of the application of this lamp to daylight signalling equipment. It describes the various types of discharge-lamp signalling equipment which have been used. In the latest type, no mechanical shutter is employed, as the arc is ignited instantaneously by a high-voltage impulse circuit operated by the signalling key.