Railway signal lamp incorporating safety devices - includes damage or breakage indicator around, or on both sides of, colour filter

摘要

The warning lamp, particularly for a railway signal has a main filament and an auxiliary filament with corresponding connections. The auxiliary filament is switched on in the event of failure of the main filament. A coloured filter strip around the lamp also includes a safety device in the event of damage. This can be made of a brittle substance, and is transparent. It may be a zinc oxide layer, or a substrate or an adhesive foil. In an alternative design it may consist of two concentric rings connected in series, or may be a spiral. Another alternative has conductive portions on opposite sides of a colour filter.