Best Viewing = fluorescent 110v. You can find tubes that fit in standard small fluorescent fixtures, at your local hardware store. I see most at rummage sales. Disadvantage, not portable, too large to take on trips. But they have the best wavelength for making the markings show up.

Best Midsize = Small battery operated fluorescent. Find them at coin shows and hobby shops. Good light, good exposure. Buy rechargeable batteries if you are going to use it for long periods. Roughly 6 inches x 1 x 2. (pet store idea was good)

Best Small = One of the LED keychain versions like people have shown here. They don't have the best wavelength, but they work well. Probably will run for years on the original battery.

Not Recommended = standard light bulb versions, which are weak, run hot, don't show UV very well, and are not portable.