Effects of plexiglass on plant growth

When you cool grow box lights by walling them off with plexiglas, does that reduce the effectiveness of the lighting? Would it slow plant growth?

I'd like to get the temp down in my 2X2X3 grow cab, and I'd like to have more lights, so I thought I would seal the (CFL) lights off with a sheet of plexiglass.

Is that an efficient/effective way of doin' things?

That's how cool tubes are made. Plexiglas won't eat the light like glass will. Just put a thin layer. But with CFL's it shouldn't be to hot.