This is our automatic photocell daylight sensing replacement 15-LED bulb, which automatically comes on at dusk, and turns off again at dawn. It is a drop in replacement for your existing Aqua Signal, Hella, Perko or other anchor light or tri-color housing with a BAY15D bayonet base (double-contact, offset pins) socket. No extra sensors, wires, or switches needed. We have built all of the daylight-sensing electronics right into the bulb, so it is just a simple replacement. The bulb still features the Marinebeam constant-current electronics, and 15 of the newest multi-emitter LEDs, so its output far exceeds all requirements for all-around anchor lighting for boats up to 20M (65 ft). Perfect for boats on a mooring, or for cruisers constantly on the hook. Never forget to turn off your anchor light again! Fits Aqua Signal Series 40, 41, 42,& 50 as well as Hella 2984 and Perko 200 Fixtures. Replaces Aqua Signal Bulb 90002, 90003, 90005, and 90006 , Hella Bulb # 78290 and Perko Bulb # 037512V10W Cross References to Hella bulbs: 8GA 003 488-121 8GA 003 488-301 8GA 003 488-131 8GA 003 488-311 Voltage: 8VDC - 30VDC Constant-Current Control Wattage: 3W Amperage: 0.25A at 12V Lumens: 240 Dimensions: Dia. 28mm x 40mm (+socket) Marinebeam bulbs feature a proprietary Constant-Current driver and high-output thermally-efficient multi-emitter SMD LED bonded to an Alumicore engineered thermal substrate. All our bulbs can operate on any polarity, and have a custom EMI suppression circuit to prevent interference with radios, GPS, etc. These features combine to give record setting output, superior efficacy (lumens/watt), and the longest service life possible in an LED cluster.