A viable safe test would be a clear (unfrosted) incandescent or halogen bulb on a rheostat. Glasses on, bulb off, turn up the brightness somewhat slowly. You sh

A viable safe test would be a clear (unfrosted) incandescent or halogen bulb on a rheostat. Glasses on, bulb off, turn up the brightness somewhat slowly. You should be able to look directly at the filament comfortably if you have good glasses. If you have fakes, as long as you ramp up brightness slow enough, your natural response to squint will kick in before you wreck your retinas. You definitely do not want to test this on the sun.