By Seth Porges

When is a light more than just a light? When it's an alertness-enhancing, reaction-time-raising, energy-giving stimulant.

For centuries, it was assumed that our eyes did little more than see the world around us. But in the late 1990s, researchers discovered that, in addition to vision-enabling rods and cones, our eyes are filled with a special photopigment called melanopsin, which uses light to trigger a series of responses that have little to do with our conscious sight. And, for reasons that scientists can only speculate on, melanopsin is particularly sensitive to the short wavelengths of blue light.

"Blue light improves reaction time, improves subjective alertness, and changes EEG activity, showing that the brain is in a more alert state," says Dr. Steven Lockley, associate professor of medicine at the Division of Sleep Medicine at Harvard Medical School, and coauthor of Sleep: A Very Short Introduction.

Much of this response derives from the fact that blue light has been shown to inhibit the body's production of melatonin—a sleep-inducing hormone that helps us maintain our circadian rhythms. "Basically, blue light signals to our bodies that it's daytime, and that we should be awake and alert," says Dr. Randy Nelson, professor and chair at the Department of Neuroscience at Ohio State University.

Although researchers have known about the powerful stimulating effects of blue light for more than a decade, practical, consumer-friendly applications of this knowledge have been limited. Although there are a number of light boxes designed to treat Seasonal Affective Disorder—a depression brought on by certain times of year, usually winter—that give sufferers an extra jolt of artificial daylight, there's currently not much for the average person.

But that could soon change. That's because, in addition to being incredibly energy-efficient, modern LED lights also have the benefit of being digitally programmable. With incandescent and compact fluorescent bulbs, it is very difficult to create a single fixture that can offer a wide range of color and brightness settings. With LEDs, adjusting these settings is as easy as flipping through TV channels.

This means the therapeutic potential of LED lights is massive. In the future, we'll likely see fixtures that automatically adjust their color and brightness as the day transpires. These lights could even use RFID chips, smartphone apps, or other sensors to adjust their settings based upon the unique needs of people who are present.

"Before you go to bed, you might want a red-enriched light to help you fall asleep, and then blue-enriched light during the day to help you stay awake," says Dr. Lockley, who is currently working on a study with NASA that he hopes will result in a lighting system that will improve mood and productivity aboard the International Space Station. "A light system could even know if you have an important meeting at 3 o'clock or an important dinner at night, and then give you a blue light boost to make you alert."

Such smart lights would be especially helpful to the roughly 20 percent of American workers who work evenings and nights. Shift work has made these workers not only particularly susceptible to sleep problems, but to elevated rates of depression and metabolic disorders.

And that's not to mention the millions of people who live in a caffeine- and sleeping pill-saturated society. For countless Americans, LEDs could prove to be an inexpensive and non-invasive way of tackling those twin towers of modern society: staying awake and alert during the day and asleep at night, problems that researchers believe act as dominos that trigger a host of other health issues.

"I've been suggesting for the past year or so that perhaps these twin pandemics of obesity and depressed mood may be related to our exposure to bright light at night," says Dr. Nelson. "As cultures electrify their nights, you see increases in these rates, but new blue-enriched LED lights could help this."

Seth Porges is a technology journalist, editor, and columnist whose work has appeared in Popular Mechanics, Bloomberg News, BusinessWeek, Men's Health, PC Magazine, and many other publications.