The Health Impact of Light

The Health Impact of Light

Circadian rhythm: Important to overall health

Often referred to as the "body clock," the circadian system is a roughly 24-hour cycle that tells the body when to sleep and also regulates many other biological functions such as hunger, body temperature, blood pressure, growth (in children), and the timing of the release of melatonin and cortisol. When circadian rhythm is in tune, the body's cycle of alertness, mood, and sleep are optimized and stable, which helps maximize sleep quality and recovery.

What doctors are saying

"Light affects our circadian rhythms more powerfully than any drug."

- Charles A. Czeisler, MD, Director,
Division of Sleep Medicine,
Harvard Medical School Harvard Medical School

"The primary human concerns with nighttime lighting include ... potential carcinogenic effects related to melatonin suppression, especially breast cancer. Other diseases that may be exacerbated by circadian disruption include obesity, diabetes, depression and mood disorders, and reproductive problems."

- American Medical Association official statement on
nighttime lighting. American Medical Association

"Many studies have found that lighting has a significant biological effect - impacting sleep, alertness, and many other physiological functions."

- Louis Sullivan, MD - Former U.S. Secretary of Health and
Human Services Health and Human Services

How light can affect circadian rhythm and potentially health

Light is one of the most significant factors affecting sleep and circadian rhythm. It has two major effects on patterns of alertness and sleep. First, the timing of the circadian rhythm is synchronized by the 24-hour light-dark cycle, so daily exposure is required. Second, light is a stimulant and can increase alertness and performance.

Special cells in the eye detect light and send this information directly to the areas of the brain regulating circadian rhythm and alertness. These cells respond differently to different wavelengths of light and are most sensitive to blue wavelength light. The sun emits a spectrum of light with high blue wavelength content, telling the brain that it is daytime and signaling the body to be more alert. This natural cycle of light and dark synchronizes the "body clock" to the 24-hour day.

New LED lighting technology can control the spectrum of light emitted to mimic this natural cycle and help provide the right type of light at the right time of day. For example, LED pre-sleep lights emit very little blue light, encouraging the body to release melatonin, the hormone that tells the brain that it is nighttime and to get ready for a peaceful night's sleep.

How some light can disrupt circadian rhythm

Fluorescent, CFL and normal LED light bulbs emit a spectrum of light with a high concentration of blue wavelengths, which tells the brain to wake up. Similarly, computer and electronic device screens also emit concentrated blue wavelength light.

When exposure to blue-enriched light occurs just prior to bedtime, it can wake you up and may disrupt your sleep cycle. Other rhythms can also be affected by the change in light, including cognition, metabolism, and mood.

Recent lighting breakthroughs to help manage circadian rhythm

Today, new technology has enabled the production of LED lights specifically engineered to help facilitate a healthy circadian rhythm. Some are designed to filter out blue light wavelengths, promoting better sleep patterns, which can strengthen the immune system. Others emit increased blue wavelength light, promoting greater energy and attentiveness.

The technology behind these advanced light bulbs, which are now available commercially, is founded on the same principles NASA used on the International Space Station to improve the sleep and performance of astronauts by mimicking a normal day/night cycle.

New products like these and recent studies by major universities and health organizations have increased the public's awareness of the close link between light and health. The technology provides new options to help support good health by using the right light, at the right time, for the right task.

When looking for lighting, use the spectrum below to understand a bulb's light wavelength content. Those with high blue content should help with alertness while those with low blue content are more likely to support sleep and restoration.

What doctors are saying

"Light affects our circadian rhythms more powerfully than any drug."

- Charles A. Czeisler, MD, Director,
Division of Sleep Medicine,
Harvard Medical School

"The primary human concerns with nighttime lighting include ... potential carcinogenic effects related to melatonin suppression, especially breast cancer. Other diseases that may be exacerbated by circadian disruption include obesity, diabetes, depression and mood disorders, and reproductive problems."

- American Medical Association official statement on
nighttime lighting.

"Many studies have found that lighting has a significant biological effect - impacting sleep, alertness, and many other physiological functions."

- Louis Sullivan, MD - Former U.S. Secretary of Health and
Human Services

The Light Wavelength Spectrum

the light wavelength spectrum the light wavelength spectrum

Learn More