Bill Howatt
I put a light in my door which was the typical molded hardboard slab door with the corrugated cardboard inside.

I layed it out, drilled a hole and and cut the opening with a jig saw. Had to take a chisel and cut out some of the cardboard and hot glue so I could fit in some 1x1-1/8 between the front and back panel. I then cut some pieces to hold the glass and trim the opening.

Bill