I do double-sided pcb boards with glass in both sides with only one source of light (fluorescent) without problems. The only you have to take into care is the time each side is exposed to the light source is a little less compared to a one-sided pcb.
2014-03-28 17:04 GMT+01:00 <alienrelics@...>:
Yes, the top should be opaque. It doesn't have to be glass. I had a piece of wood with a sheet of glass on a hinge.
Steve Greenfield AE7HD