maybe a deep violet right at the edge of the visible spectrum? all you would see is a faint glow

I'm not sure but I heard short wavelength (blue/violet) visible light has most impact on circadian rhythms.

If it's indeed the case, insomnia or any other kind of sleep disorder is not worth it.

Ok, but you'll be the one to explain to people who don't want to accept the ionizing/non-ionizing radiation distinction that this sort-of-UV is not the cancer-causing UV.