The patch is the light texture itself. In Doom 3, the breakable lights resemble a light entity surrounded by a brush with the default texture. Interestingly, after pulling apart the Doom 3 maps, the light patches which are merged or grouped with this light entity appear green in the main viewport and some distance away from the main light entity itself. Obviously, in order for the effect to work properly they must be grouped together, but there is no discernible way to do this in DarkRadiant. As you can probably tell, I'm learning mostly through reverse engineering and trial and error haha.