Great for lighting your boat, house, deck or the area around your pool or fountain, fully marinized. They switch on automatically in the dark and provide up to 8 hours of light on a full charge. The on/off switch allows you to turn the rail light off. Rail lights use Fast Solar technology, a charging system optimized to recharge the internal battery in overcast and cloudy conditions. Even when the switch is in the off position, the battery continues charging. Fits rails .65"-1.25" diameter.