Letting in a little extra light throughout the day may do more than just lift your spirits. It could make you more alert and help you avoid an afternoon energy slump.

Ambient light influences brain functions and different aspects of human physiology such as circadian rhythm, heart rate, and hormone release. While these functions have been recognized and studies have looked at the part of the brain that induces these responses at nighttime, little has been known about daytime responses to light.

But Gilles Vandewalle of the University of Liege, Belgium, and colleagues wanted to see if light exposure has similar effects on brain function during the day, when we are naturally exposed to light.

The researchers exposed a group of people to 21 minutes of bright white light in the morning while they imaged their brains. Not only were the participants more alert, but responses in certain parts of their brain also got a boost.

This boost was correlated with regions of the brain that are involved in alertness and some cognitive processes and can briefly prevent the sleepiness developed in continuous darkness, the researchers report in the Aug. 22 issue of the journal Current Biology.

The brain regions that were affected by light are also typically involved in attention and arousal regulation, Vandewalle told LiveScience. "So light affects these regulatory systems at the cerebral and behavioral level. This could be relevant for demanding jobs for example, usually performed by tired people."

Tired people can be found in offices everywhere from the equator, where the sun shines down directly, to the Arctic Circle, where for half the year folks get much less direct sunlight.

"People stay inside most of the time everywhere on the planet," Vandewalle said, adding that people should expose themselves to natural light in all countries, since light outside is always brighter than what we get in offices.