I read an interesting article by someone that set up "daylight" lighting in their home by essentially tiling their entire ceiling in high-efficiency LED panels. He offset the electricity costs using solar power and batteries.

The gist of it was that it very markedly improved the mood and general wellbeing of his entire family, and visitors would often comment about how "nice" his house was without being able to explain precisely why they felt that way.

Conversely, imaging living and working in a dark cave.