Their are times in a fountain application and sometimes swimming pool area (not within a swimming pool) where a fixture may not be fully submerged yet still gets wet. For example a fixture that is mounted behind a waterfall feature yet above the pool of water.
The Hydrel line of wet/dry lights is designed especially for use in areas of water features that are prone to being dry or could possibly be dry much of the time. These versatile fixtures can operate totally submerged but, unlike other underwater lights, do not depend upon water for cooling and therefore continue to operate even when water levels are low. This feature makes the wet/dry fixtures ideal for use on the edges of waterfalls, streams, or fountains and in installations with a fluctuation in water level.