Great thread! I think I'll do this...when I have money for making a HID. I just wanted to expand on the idea of using a hurricane candle shade for a larger diameter. I just popped that into google and found a site that sells the contoured ones, as well as a straight tube design. Here is a link to that:
Connie's Creations Candles - Hurricane Globes & Shades
Obviously go wherever you want for it, I just didn't even think that there would be a straight-shot one.
