Darn, I thought I was being so clever using my folding Ott light under a sheet of plexiglass from Home Depot - now I find out everyone's doing it!
I prop the plexiglass up on whatever's handy, usually plastic shoe boxes holding fabric pieces. It all sits on my cutting table, so it's a good height to work standing up. Previously I tried using a window, but the angle was bad, and you can't use that method at night or if it's not a sunny day.