Abstract: The present specification describes and claims a light dependent device for use in motor vhicles, for monitoring the environmental light and providing warning when regulation lights on the vehicle should be switched on or off. The device comprises a light sensor connected to a switching element which is adapted both to be connected to the light circuit of a vehicle and to, in use, switch when the intensity of the light falling on the light sensor passes a level at which regulation lights on the vehicle should be switched on, and a warning device. The warning device is arranged to be activated by the switching of the switching element when the light intensity falls below said level and to be deactivated by the switching element both when the light intensity exceeds said level and, when in use and connected in the lighting circuit of a vehicle, when the regulation lights are switched on.