Blue Light Sets Body Clock

Your body's internal clock is more sensitive to shorter wavelength blue light than it is to longer wavelength green light.

That's the conclusion of a study by researchers from Brigham and Women's Hospital in Boston and Jefferson Medical College in Philadelphia.

The study findings prove what's been suspected for about a decade -- that a second, non-visual photoreceptor system influences the body's internal clock, which controls sleep patterns and other behavioral and psychological functions.

"This discovery will have an immediate impact on the therapeutic use of light for treating winter depression and circadian disorder," George Brainard, a professor of neurology at Jefferson Medical College, says in a news statement.

He notes that 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. Broad changes in general architectural lighting may take years, but the groundwork has been laid," Brainard says.

He and his colleagues tested 16 healthy people who were exposed to the same amount of blue or green light. The researchers measured the effect of the two kinds of light exposure on the timing of the study participants' biological rhythms.

Blue light was twice as effective as the same amount of green light at resetting the internal biological clock.

In previous research, Brainard and his colleagues found wavelengths of light in the blue region of the visible spectrum are most effective in controlling the body's production of melatonin. It plays a major role in the body's circadian rhythms.

More information

Here's where you can learn more about your body's clock.

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