The round housing of these vapor-tight fixtures holds a bulb to illuminate small, damp or humid areas. Sometimes called jelly jars, they surface mount to walls or ceilings and are commonly used to illuminate boiler rooms, basements, and lower-level hallways. Their housing and lens fit tightly together and seal with a gasket to prevent dust and moisture from entering the fixture and damaging internal parts. They are rated for wet locations with occasional water drips or light sprays.