I almost invented it

The gardens get lots of shade, but it's mixed with shafts of morning and afternoon sun, so I could never decide whether I had partial shade, partial sun, or what. I had often thought that there must be a way to measure the amount of sunlight that falls, perhaps with sun-sensitive paper or some such. Well, it turns out that such a device exists, as I discovered in the Lee Valley catalog (thanks, Martha!). So far I have tried it in two spots - the new garden along the back of the house, and the narrow strip along the path-to-be along the side. Both came up as partial shade. Now I just have to understand what exactly they mean by that...