My university has clean rooms, they have windows, the hallways have windows too so you can peek in from outside. Always great to show to visitors :) (at night they have weirdly colored lighting, pink, purple, so it looks really funky, no idea why)
It's possible that when nobody is working in the room, the lights aid in maintaining a sterile environment.
At specific wavelengths (~245-265 nm), (UV) light inactivates quite a few living things. As light is quantized, the purpleish color you see is due to e- stepping down.
My UVC bulbs deployed in a FL home water treatment system pipe out UV in the region of 253.7nm. An ophthalmologist friend pointed out that unfiltered long term exposure to these wavelengths first catalyzes conjunctivitis (pink eye) then conditions go down hill from there. It's suggested that you don't stare directly at sources of this purplish color for any protracted periods.
Nope. Our bio hoods have a toggle switch. Lights off is in the middle, lights on is one direction, UV sterilization is the other direction. To turn the lights on, you have to turn the UV off.
Clean rooms that work with semiconductors use light-sensitive photoresists. I've always dealt with yellow windows and yellow covers over the lights, though in theory pink would accomplish the same thing: keeping blue light off the wafers while you're working with them.
The concept is not at all dissimilar to old-fashioned darkrooms in photography. Outside light will wash out your image.
Certain parts of the cleanroom will look yellow--these are the spaces where they do lithography with resists that are openly accessible to the air. UV-sensitive resists will chemically crosslink in UV light, so they put on filters on the fluorescent lights (or use special lights) that keeps the wavelength away from the higher-energy blues and towards the lower-energy yellows and reds.
