These portable marking lights are powered by a maintenance free 3.6v Nickel Metal Hydride battery. A mono crystal solar module fitted inside the lens keeps the battery fully charged and can provide enough power to keep the beacon operating non stop for 400 hours in continuously cloudy and rainy days. A built in photocell switches the beacon on & off at dusk and dawn. The On/Off level is between 70/100 lux and is automatic. The unit incorporates an automatic switch after 18 hours in the dark to protect the battery life.