I know what you mean by this .. no artificial lighting or whatnot. I think it should be pointed out, though, that scorpions do use light to maintain a circadian rhythm. So they do need some sort of regular light cycle to .. well, effectively to keep them from getting jetlag. That being said, the faintest bit of sunlight coming in from the cracks in a blind of a basement window is going to likely be sufficient to give them a fluctuating light level. In their night-time sensitivity state the eyes of scorpions are some of the more sensitive photoreceptors out there.They don't need any lighting at all.
They should be sensitive to the bulb only as heat and not as light. Certainly it would seem it is outside of the spectrum that they perceive and can use to entrain their circadian rhythm. That being said, I'm a huge fan of night-time temperature drops so I would suggest creating such a drop regardless of how you are heating the tank. That's just a personal take, though -- provided you aren't baking them, they aren't going to be harmed by that light.I use a 75w infrared light for a 20 Gal tank. Is it OK to leave it on 24/7 or should I dim/shut it off through the night?