Jefferson and Brigham and Women's researchers find blue light important for setting biological clock

Researchers from Brigham and Women's Hospital (BWH) in Boston and Jefferson Medical College have found that the body's natural biological clock is more sensitive to shorter wavelength blue light than it is to the longer wavelength green light, which is needed to see.

The discovery proves what scientists have suspected over the last decade: a second, non-visual photoreceptor system drives the body's internal clock, which sets sleep patterns and other physiological and behavioral functions.

"This discovery will have an immediate impact on the therapeutic use of light for treating winter depression and circadian disorders," says George Brainard, Ph.D., professor of neurology at Jefferson Medical College of Thomas Jefferson University in Philadelphia. "Some makers of light therapy equipment are developing prototypes with enhanced blue light stimuli."

"In the long range, we think this will shape all artificial lighting, whether it's used for therapeutic purposes, or for normal illumination of workplaces, hospitals or homes – this is where the impact will be," he says. "Broad changes in general architectural lighting may take years, but the groundwork has been laid."

In theory, he says, "If a clinician wants to use light therapeutically, the blue wavelengths may be more effective. If you wanted built-in illumination that would enhance circadian regulation, you might want this wavelength region emphasized. It is interesting that natural daylight – the blue sky – is rich in this part of the spectrum."

Dr. Brainard and his co-workers previously discovered that wavelengths of light in the blue region of the visible spectrum are the most effective in controlling the production of melatonin, which plays an important role in the body's circadian rhythms.

The scientists reported their findings September 9 in the Journal of Clinical Endocrinology and Metabolism.

In the study, researchers tested 16 healthy subjects, exposing them to the same amount of blue or green light. They measured the effect of the light exposure on the timing of their biological rhythms. The researchers found that blue light was twice as effective as the same amount of green light at resetting the internal biological clock.

Dr. Brainard, who is also associate team leader for the Human Performance Factors, Sleep and Chronobiology Team of the National Space Biomedical Research Institute, sees the work as having potential impact on sleep disorders involving space travel.

Sleep disorders are extremely common, affecting as many as 40 million Americans.

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