mtbc | Sunbeams for troglodytes

I was wondering about blue to ultraviolet light and living partially underground in sunny places. If one did have many subterrean chambers, for instance if living in a harshly hot or cold region, then I wonder how to get enough useful light for managing one's circadian rhythm, making vitamin D, growing plants, etc.

One may use skylights and sun pipes and whatnot though I don't know how easily one can obtain ones transparent to sufficiently high frequencies. Or perhaps electrical lighting can be useful, whether daylight spectrum or even ultraviolet: put it in one's farming rooms and turn it off when attending to the plants personally to avoid eye burns or other injury. I am ignorant of the types of ultraviolet light such as to what extent the useful frequencies are also the dangerous ones.

I guess that it is inefficient to use solar panels and electrical lighting to move sunshine underground. Maybe there is even some kind of plastic sheeting one may inflate with water to make a lens over a tunnel to act as a solar collector to direct much light and warmth to a deep sheltered trench; I wonder how well refractive index correlates with density. There could be a few ways to meet various requirements and some may even make sense.

Update: I hear on the radio that daylight-spectrum lighting can be used for growing potatoes.