Panel and troffer light fixtures mount in drop ceiling grids to provide general lighting for large open areas and hallways. Also called recessed panels or troffers, they keep the majority of the fixture concealed in the ceiling for a clean look that doesn't draw attention to the fixture. The fixture height must be less than the height above the ceiling for a proper fit. LED light panels and troffers use less energy than fluorescent troffers and have built-in LED arrays so there are no light bulbs to install or replace. Fluorescent troffers use fluorescent light bulbs and some types of LED bulbs. Light diffusers fit onto panel or troffer fixtures to provide a filter that softens light and spreads it further across a room.