A retrofitting kit includes at least one of an adapter bracket and a retainer configured to engage at least one of an existing troffer light fixture and a T-bar of a ceiling system and a door assembly configured to be held in the ceiling system by the at least one of the adapter bracket and the retainer. The door assembly includes a lens, a housing configured to hold the lens, the housing including one or more sidewalls disposed around a periphery of the lens, where the one or more sidewalls extend upward, away from the lens to define a cavity, and a plurality of LEDs having primary light axes extending inward into the cavity. The plurality of LEDs are coupled to the one or more sidewalls and positioned to illuminate the lens from behind with a uniform distribution of light when engaged.