1. An automatic light system for controlling the light emission of a vehicle headlight, comprising: light sensor means disposed within the darkened engine compartment of said vehicle to receive ambient light, control means for automatically turning on or off the headlight in response to detected light level signals from said light sensor means when said light level signals are within predetermined light level ranges, delay means for preventing the turning on or off of the headlight if the detected light level signals do not stay within the predetermined light level ranges for a predetermined period of time, polarity switching means connected between said vehicle headlight and the poles of an electric power source, for selectively switching the polarity of the voltage applied by said power source to said headlight, whereby on and off control of the headlight is accomplished without being affected by momentary, sudden darkness or light and additional battery drain during vehicle starting is prevented.