You’re probably already aware that eating off extra-large plates can translate into consuming extra-large portions and that watching TV during a meal may distract you enough to make you overeat. The latest research on restaurant ambience examined how bright versus dim lighting affected diners’ food choices.

The study had several different prongs. The first involved a survey of 160 patrons at casual chain restaurants. Those sitting in brightly lit rooms were 16 to 24 percent more likely to order healthy foods (such as grilled fish or chicken and vegetables), while those in rooms where the lights were dimmer were more likely to order unhealthy items (like fried food or dessert). Plus, those eating in darker dining rooms ordered 39 percent more calories.

The researchers then replicated these results in four additional lab studies, involving 700 college-aged students. A surprising finding was that when the students were given a caffeine placebo — or even just told to be more alert — those dining in dimly lit rooms were now just as likely as those in the brightly lit rooms to make healthy choices.

This led the researchers to theorize that it’s not the lighting itself that affects our decision making, but how alert we feel while we’re ordering. “We feel more alert in brighter rooms and therefore tend to make more healthful, forward-thinking decisions,” says the study’s lead author, Dipayan Biswas, Ph.D., a professor of marketing at the University of South Florida.

However, a 2012 study actually found that dimming the lights in fast-food restaurants resulted in people eating more slowly, eating less overall and enjoying their food more, so turning down the lights in your eating environments isn’t necessarily a bad idea. Just make sure you’re feeling alert enough to order something healthy when you sit down. How about taking a brisk walk around the block before you head into the restaurant?

Sally Wadyka is a Boulder, Colorado-based journalist who writes about nutrition, health and wellness.