You may know this bright light-accumulating paint so popular for dying one's face with mysteriously glimmering pinkish, bluish, yellowish and greenish ornaments on Halloween eve.
My idea is painting whole rooms with this paint that would accumulate light during daytime, then emit it at the nighttime.
This painting is so bright and pleasantly-colored so it would be a great mean for coping with depression and bad mood on long autumn evenings.

plus wouldn't it be fun to live in such rooms, naturally-lit at night?