Panel and troffer retrofit kits convert fluorescent troffers to LED technology or more energy-efficient types of fluorescent bulbs to reduce operating costs. The LED retrofits generally require less maintenance and use even less energy than fluorescent fixtures fitted with plug-and-play LED light bulbs. Also called door kits, retrofit kits fit into the housing of an existing fixture so the fixture doesn't have to be completely removed, replaced, and rewired. To assist with future maintenance, a sticker or label can be placed on the retrofit upon installation to indicate that the fixture components have been modified from their original form. Panels and troffers are used in grid ceilings to provide general light for large open areas and hallways.