You'll be happy to hear this. It's one of those scientific studies that tells us something we think we all know anyway--but we're really glad now to have some proof.

Researchers in the United Kingdom designed a human lab experiment in which they used "happiness shocks" (which sounds a little R-rated, actually, but isn't) to improve workers' moods and measure how happiness affected their productivity.

The results will make you smile. (I first read about this study in Michael Addady's article in Fortune.)

Testing more than 700 university students who volunteered for the experiment, they assigned them job tasks, but interrupted some of the participants from time to time to do things like give them fun snacks and drinks, or show them a 10-minute clip of a funny movie.

(Technically in psychology, this technique is called a "mood induction procedure," but these researchers coined the term "happiness shocks," and it's funnier, so let's use that one.)

The researchers followed up with questions designed to ensure that the participants actually enjoyed the little breaks and felt happier, and later gauged their productivity.

The results? Workers who were exposed to happiness shocks were 12 percent more productive than those who weren't, and some of the happy workers were 20 percent more productive. In economics, increasing productivity by just 3 percent would be "considered very large," the study notes, and yet the cost of the happiness shocks were very cheap.

Granted, these were university student in a lab--not real workers slogging away at their TPS reports, dealing with overbearing bosses, and wondering whether they were going to get out of work on time to pick up their kids from school. As a result, the researchers (at the Social Market Foundation and the University of Warwick in England, led by Daniel Sgroi) suggest that further research in real-life situations would make sense.

"The scale of the effect makes it likely that even close to zero-cost 'nudges' would have impact. This is an important idea to test in practice," Sgroi writes. The researchers did an additional experiment studying the effects of real world "unhappiness shocks" like "bereavement and family illness" on productivity, and concluded that the negative effects usually last about two years.

Bottom line: If you want more productive workers, make them happier. Science says it works.