Retrofit systems and methods are disclosed for lighting installations, and in particular, to retrofit systems and methods used to retrofit troffer-style lighting installations with LED light sources. Retrofit systems can be used with different light fixtures, but those described are particularly adapted for use with troffer-style fixtures. These retrofit systems can provide the same amount of light as traditional light fixtures already do, for example 1600-4000 lumens or more. The retrofit systems can be used with many different light sources but are particularly well-suited for use with solid state light sources or light engines, such as those utilizing LEDs. Some embodiments of the present invention comprise a mechanical mounting system for installing an LED light engine within an existing lighting system housing or pan, such as a troffer pan, without penetrating the ceiling plenum.