A retrofitting kit for retrofitting an existing troffer light fixture having a troffer housing includes a door assembly and a retainer including a flange. The flange is deformable between a first position and a second position. The light source is within the housing. The retainer includes the flange coupled to the housing of the door assembly. The retainer is configured to engage at least one of the troffer housing and a T-bar of a ceiling system to thereby selectively secure the door assembly within the ceiling system when the flange is in the first position. The retainer is further configured to facilitate at least one of installation and removal of the door assembly when the flange is in the second position.