In one aspect, a light fixture includes a light source configured to emit light, a driver configured to control operation of the light source and a body housing the light source and the driver. The body is rectangular and configured in length and width so as to slide into a prismatic lens frame of an existing light fixture installed in a ceiling, fill in the frame and be held in place by the frame, where the frame is configured to hold a translucent prismatic lens and close on the existing light fixture. The body of the light fixture is also configured to fit between a body of the existing light fixture and the closed frame. The body is configured in thickness along the perimeter such that the perimeter of the body is able to slide into, fill and be held by the frame.