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No, what you're seeing is the lower end of visible light that's also emitted by the uv lamps. They're emitting a lot below 400nm that doesn't pass through your lens. Unless you've had surgery that removes or thins your lens.

Letting uv in is bad in general because it's very damaging. The evolutionary question is rather what benefit the reindeer get that overcomes the drawbacks of increased retinal UV exposure.

Those lights (like most lights) give off a broad range of frequencies. The blue / violet parts that humans can see are by definition not "ultra"violet (beyond the visible spectrum). Even if we could see those frequencies, not much would be needed to explain it other than it helps us see certain things / under certain conditions better.

I can see it as well. I think it's due to spectra from the bulb spreads into the visible portion, with peak emission at UV-A.

No, that’s just purple light, that is produced along with the UV and not perfectly filtered out.