A dive light is a light source carried by an underwater diver to illuminate the underwater environment. Scuba divers generally carry self-contained lights, but surface supplied divers may carry lights powered by cable supply from the surface.
A dive light is routinely used during night dives and cave dives, when there is little or no natural light, but also has a useful function during the day, as water absorbs the longer (red @ 3 feet) wavelengths first then the (yellow @ 9 feet) depth. By the time you reach 30 feet everything will look grey. By using artificial light, it is possible to view an object in full color at greater depths.
Kirk Scuba Gear Offers all three suggested kinds of dive lights:::Primary, Secondary and Video