Twilight switches with a separate light detector from F&G are detector from F&G are designed for installation in switchboards on 35mm mounting rails according to DIN EN 50022. Twilight switches are used for the automatic control of lighting systems depending on the natural daylight level. The enclosed weatherproofed light sensor detects local brightness at the mounting location. The response threshold is infinitely variable and set by a rotation thumbweel on the front of the twilight switch. The field of application covers electrical installations in trade, industry and the home, e.g. control systems of window-display advertising, indoor and outdoor illuminations, display lighting, illuminated signs, street lighting etc.