If you are going to use a large piece of glass and a light bulb I would get the bulb as far away from the glass as possible to avoid inverse square law falloff. You don't want the distance from the bulb to the sides to be further than the distance to the center as the result will be an image darker in the center. You may want to use several bulbs to give an even light. Azo requires quite a bit of light anyway. Make sure you ask them to grind the edges of the glass to remove the sharp corners or your fingers may suffer.