According to Nicholas Diakopoulos, in his blog post on hbr.org, data visualization works best when we’re happy.
Anyone who must present information in a visual way — from designers to managers — is at the mercy of the ever-changing attention spans of their audience. As numerous psychological studies have shown, our moods have a big impact on the ways we process information; the happier we are, the less likely we are to make reading errors, for example. So the key to getting your message across, in theory, is to prime your audience with positive feelings — warm colors on the page, a lighthearted joke in person. Of course, emotional manipulation has its limits. Balance, in other words, is key.