I have a ton of these in my yard with solar lights. I started a thread on DG in the Trash to Treasure forum about it in 2007. There are lots of great photos here from folks who have tried this.
The solar light has to sit on top of the opening so its collector is exposed. Frosted glass works fine---I even have one that's amber that looks really nice.
What I do with the more open glass pieces is put a plate, wide enough to completely cover the opening, over the top. Sometimes I can find a plate with a hole in it, and sometimes I have to drill it. The solar light sits on top of the plate. This arrangement keeps leaves from falling into the globe.
Some solar lights have two bulbs, which work really well. Some also have plastic diffusers attached that go down into the globe and make the light shine farther down into the longer glass fixtures.
I got my last set of solar lights from eBay. That's where I found the ones with two LED bulbs.
This photo is the "before" photo of a lamp I got from Freecycle.
This is the "after" photo. The lamp has a bulb for reading, and when it's turned off, the solar kicks in so it still lights up. You can see the plate over the top, with the solar collector on top of the plate. The bulb fits through a small hole in the plate so it lights up the globe.
