"White nights" are what the Russians call the pale summer nights of midsummer according to the movie by the same name. In Norwegian, the term is "blond nights" but most people just say "long, light summer night". Because that's what is.
I am talking about this because Jon asked me a question in a comment: Do the wonderfully long days help [my good mood]?
And I answered truthfully that I was actually getting a bit sleep-deprived because the lack of true darkness messes with the circadian rhythm. But in general, yes, more daylight does brighten the mood as well as the world.
The long pastel evenings of summer are gorgeous. Being able to sit out in the sun until well past 10 pm is wonderful. But the lack of proper darkness throws off one's inner clock, so lately my usual in-bed-by-10 routine has become in-bed-by-11:30 (which leaves me tired in the morning because 8 hours of sleep is needed all year round).
Case in point: Last night I was getting ready to go to bed because I finally yawned. I looked out my window and had to get my camera. This is last night's sky at 11:24 pm, looking northwest: