People dining in brightly lit restaurants make healthier choices because they are more alert, a new study finds.

Dining in dimly lit restaurants has been linked to eating slowly and ultimately eating less than in brighter restaurants, so researchers at the University of South Florida decided to see if lighting also impacted how healthfully people order.

First, the researchers surveyed 160 restaurant patrons at four casual chain restaurant locations. Half of those diners, who were seated in brighter rooms, were more likely to choose healthier options (such as grilled/baked fish, vegetables or white meat) over relatively unhealthy items (such as fried food or dessert).

Furthermore, sales records showed that those in dimly lit rooms actually ordered 39 percent more calories. In four additional lab studies involving 700 college-aged students in total, the researchers replicated these results for the study, which is forthcoming in the Journal of Marketing Research.

The follow-up studies also showed that when diners' alertness was increased with the use of a caffeine placebo or by simply giving a prompt to be alert, those in dimly lit rooms were just as likely as their peers in brightly lit rooms to make more healthful food choices.  From this, the researchers conclude that the main reason that the diners made healthier choices in well-lit spaces is because they felt more alert.

"Dim lighting isn't all bad, “Despite ordering less-healthy foods, you actually end up eating slower, eating less and enjoying the food more,” says Dr. Brian Wansink, Director of the Cornell Food and Brand Lab, and the study’s co-author.  But, he adds, “Doing what you can to make yourself feel alert is the best way to avoid overindulging when ‘dining-in-the-dark.’”