One of my favorite bits of set dressing is magic glowing rocks. You see them in movies, video games, and every other manner of medium conveying fantasy settings. Personally, I'm perfectly okay with light sources with no needed fuel and operate indefinably, but I had an idea that I thought might be interesting.
What if these rocks constantly produced ultraviolet light in addition what they emit on the visible spectrum? My first thought was underground farming, but I realized that a developing society wouldn't really benefit from being able to do that. Now I'm wondering if this glowy rock is just slightly more practical luxury item that gives you a tan.
What ramifications of this magic tanning-bed stone might I missing?
Relevant details about this rock include being about as rare and easy to find as gold (unless deceased scarcity leads to something cool, of course), always glowing as bright as a candle regardless of quantity (more surface area means more light, however), and producing an amount of UV light equal to the sun as filtered through the Earth's atmosphere. Skin cancer would be possible consequence, but Romans never found out the horrible truth of lead pipes, so I doubt anyone would notice the detrimental effects of the glowy rocks. Unless I'm mistaken, of course.