The Hg bulb sounds like it is worth a try. These bulbs have an inner bulb that puts out the light and an outer bulb made of special UV absorbing glass. Still they put out more UV then normal bulbs. If the outer bulb is broken they can put out dangerous amounts of UV. The main problem you might find with them is uneven light distribution. Remember typical enlarger bulbs are very well frosted to give an even light. But at $20 a bulb it is worth a try. If nothing else you will have bought yourself a very long life and energy efficient porch light. If you do try it let me know. I have quite a bit of AZO paper and many want to try one of these to enlarge a 6x6 negative.
They also make gemicidal UV bulbs that are have no shield. The reason is for them you want to have the UV to kill the germs. But remember they bad for you as well. So don't look at the light they put out of you may wind up with Sun burned eyes.