I voted it can make things worse for the reason that the question didn't state how much sunlight exposure any person was given. In this case its not so much the sun light - but heat.
I wish I had some actual statistics at hand but several semesters ago in a class I took on the psychology of criminal behavior, we looked at some surveys done in major cities across America that pointed out during summer time in the hottest days of the year crime rates sky rocketed with temperature. Some of the cities we looked at were LA, Detroit, Chicago, Phoenix, Miami and New York City. All saw some increase in crime rates with a rise in temperature. New York was statistically the highest and Miami, the lowest (if I remember correctly - I do remember NY was the highest for sure).
As far as sun light exposure in general... well in one sense there isn't much scientific correlation except psychologically and in some cases of seasonal affective disorder. Humans are day time creatures. Our internal clocks are wired to work best during day light. People also react more positively to good weather and warmth (as apose to miserable heat). However with SAD, most cases are purely psychological. Your typical case is not just some Scandanavian at the top of the world who never sees the sun half the year. Rather its your hermit or recluse who shuts themself in a basement with not only no sun light but little social contact.
People with SAD can see some improvement with exposure to sun light and or melatonin suppliments but some are not responsive to these therapies. Some cases can be attributed to diet. During winter years in some countries, people cannot eat the same foods which can result in nutritional deficiencies. For a lot of people, usually winter months are just depressing to many people in general because its colder and darker. And not only that people with SAD often demonstrate mild problems with depression year round. And some people with SAD have no correlation to seasonal patterns at all. Rather their mood just part of a cycle (common with people who are bi-polar) or more related to dates where something traumatic occured in one's past.
There is also Reverse Seasonal Affective Disorder (IMG:
style_emoticons/default/laugh.gif) which as the name implies - a person is more depressed during summer as apose to winter. Again, few reliable studies I have seen point out any connect between exposure to sun light and these disorders.
I am not saying the Sun has no mystical relivance at all. I think the sun does empower people and can rejuvinate people's spirits. And that can reduce aggressive behavior. But I also think that excessive sun light can sap energy and drain people and just make them miserable - which can make them more irritable and more likely to act on it.
Food for thought:
There was a French researcher (like I'd ever remember his name) who wanted to study sleep patterns and the human internal clock. So what he did was set up equipment inside a cave, that had no access to day light at all and stayed there inside the cave for something like a month. (how he went to the bathroom, is beyond me). Not only did he prove that humans have an internal clock that tells us when to sleep and be active, he also found that during his isolation, he became far more depressed and actually ended up stopping the research because he was simply loosing sleep due to his state of mind. Could this purely be due to a lack of social contact? Or could there be more involved, like exposure to the sun?
At the same time, prison inmates who are locked up in isolation seem to be more prone to suffer mental problems if they have no window versus those who do. Maybe its just the isolation of being totally concealed. But maybe people really do benefit from exposure to sun light? I tend to think so. in my humble opinion.