I know what you mean about light! If you have a hard time seeing what you are doing, it is easy to get frustrated. It is almost like doing something partially blindfolded! It definitely slows down the process.
I rarely go to a mall, but went shopping with a friend last week. We went into a higher end department store. It was so dimly lit that I could not wait to get out of there. It was a depressing atmosphere, kind of hard to see the merchandise, and a lot of the employees were yawning (and no, it was not Black Friday weekend). I would think that more light means more energy flowing, more good feelings, more in the mood to buy.