Seeing the Light of Day

(Blaine Harden/twp - Twp)

For those working at night, "the idea might be to have a work environment where at the beginning of the shift the lighting is heavier in blues that suppress melatonin, then gradually it changes and becomes redder and redder," a hue that does not stimulate the eye's ganglion cells, said Richard Stevens, an epidemiologist at the University of Connecticut Health Center in Farmington.

Stevens knows how important night-shift lighting can be. It was his focus on the issue that helped reveal that women who work night shifts for 20 to 30 years have breast cancer rates 30 to 80 percent higher than their day-shift counterparts. The mechanism is still not fully explained, but studies have since shown that melatonin -- whose secretion is suppressed by nighttime illumination -- is a potent anticancer hormone.

Consistent with that, profoundly blind women also have very low rates of breast cancer, presumably because their melatonin levels are never suppressed by light.

A panel of experts convened this month by the International Agency for Research on Cancer, part of the World Health Organization, reviewed studies on animals that were kept awake at night or subjected to repeated six-hour jet lags, and several large human studies of nurses and airline flight attendants. It concluded there is strong evidence that shift work can cause cancer.

The agency's pending declaration that shift work is a probable carcinogen may not have immediate impacts, said Vincent Cogliano, who leads the IARC Monographs program. "But our findings are looked at by government agencies and scientific researchers and could stimulate additional studies."

It may also send workplace lighting officials into a quandary.

"Should we use bluish lights in night-shift work to get the alertness, or avoid it for its potential to cause cancer?" asked John Bullough of the Rensselaer center, whose research has focused on the conflicting lighting needs of hospitalized infants, who seem bothered by bright lights, and their nurses, who need good lighting to see what they're doing.

The timing, color and intensity of light are not the only variables that affect people's health. Several studies have found that the subtle flicker common in fluorescent bulbs, especially older, low-frequency bulbs with magnetic ballasts, can have detrimental effects, even though that flicker is just below most people's threshold of conscious perception.

Stories that the flicker can trigger seizures are more legend than fact, said Arnold Wilkins, director of the Visual Perception Unit at the University of Essex in England. But fluorescent flicker can interfere with eye muscle control while scanning text or images, he said, and can cause eyestrain and headaches.

Flicker is not a problem with the new compact fluorescents, though some are painfully heavy on glare. The real revolution in lighting, many experts agree, is in the form of light-emitting diodes, or LEDs, which can be tuned to any color. As they become more affordable, many say, light will become a bona fide tool for manipulating health and mood.

Until then, people struggling to get through the winter will for the most part be best off sinking obligingly into the long, gray flannel night and avoiding the midnight lighting they think they crave.

Darkness doesn't have to be about depression and loneliness, said Dave Crawford, executive director of the International Dark-Sky Association, a Tucson-based nonprofit group that advocates against unnecessary illumination.

It can be about stars, about contemplation, about quiet conversation with a friend.

"If we sprayed water all over the place here in the desert, we'd be put in jail. So why is it okay to spray light all over the place at night?" asked Crawford, adding that more than half of all mammals spend most of their waking hours at night or twilight, "including teenagers."

Light is fine -- in the day -- Crawford said. "We're trying to bring to everyone's attention that there is a night."

For the next few months, that is going to be hard to forget. ¿

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