So I bought one and went searching around my yard and neighborhood, looking for these critters on a warm evening. I didn't find any. But I did find something even more interesting, a glowing millipede! And then a bunch of them. They are about 1-1/2 to 2 inches long, and were crawling through the detritus under live oak and pine trees.
We searched the internet for information on these and found almost nothing, until we came across the website of a millipede expert from the University of Arizona, Paul Marek (see http://cis.arl.arizona.edu/PERT/people/Marek/research.htm). He told us they are known scientifically as 'Xystocheir Dissecta' (Don't ask me how to pronounce that first word!) and they are quite common under live oak trees in the San Francisco and Monterey Bay areas of California. They fluoresce, the UV light is reflected back as visible light.
I took a video of one of these guys while shining the UV flashlight on it. The blinking red light is from the 'Recording' indicator on my camera.
These millipedes glow only if you shine a UV light on them, but according to Dr. Marek, there is another species that glows like a firefly. These are bioluminexcent, they produce the light themselves, without the need of a UV light shining on them. These live in the southern Sierra Nevada Mountains. We hope to see one someday.
We will search again for scorpions and let you know if we find any.