Solar traffic lights are signalling devices powered by solar panels positioned at road intersections, pedestrian crossings and other locations to control the flows of traffic. They assign the right of way to road users by the use of lights in standard colors (red - amber/yellow - green), using a universal color code.
Most solar traffic lights use LED lamps as they are more reliable and have more advantages over other lighting devices like CFL lamps as they are more energy efficient, have a longer life span and turn on and turn off quickly. Solar traffic lights contain enclosures which house the batteries and the control panel circuitry. Existing traffic lights can also be upgraded with an auxiliary power source using solar panels for use during power failures. The other parts in a solar traffic light include a charge controller to control the charging and discharging of the battery and a countdown timer which displays the amount of time left before the battery discharges fully.
Auxiliary solar traffic lights, in addition to the existing street lights, can be attached near the primary street lights. They are useful in regulating traffic when the primary system fails. The control system in the auxiliary traffic light monitors the primary system and when the primary system fails, it switches to the auxiliary system. Switching from primary system to the auxiliary system and vice versa can also be achieved using a hand-held transmitter unit.
Solar traffic lights can also be used during periods following natural disasters, when the existing street lights may not function due to power outages and the traffic is uncontrollable. Street lights used in such scenarios are designed to be portable enough to be carried and operated by police and relief workers wherever traffic needs to be regulated.