Reported February 2006

BACKGROUND: Researchers at Rensselaer Polytechnic Institute are studying how light -- especially blue light -- affects our body's daily rhythms. By getting enough blue light at the right time and blocking it out at other times, it is possible to correct distorted sleep patters for the elderly who tend to wake up too early, teenagers whose internal clock is usually set for late nights and sleep-in mornings, and shift workers.

HOW BODY RYHTHMS WORK: Circadian rhythms are biological cycles in the body that repeat approximately every 24 hours, including the sleep/wake cycle, along with body temperature, hormone levels, heart rate, blood pressure, and pain threshold. The brain has its own internal "pacemaker" that determines when nerve cells fire to set the body's rhythms. Scientists, however, can't precisely explain how it does so.

The colors of the light spectrum can affect the body's rhythm differently, particularly when it comes to sleep patterns. For instance, daylight is dominated by short, visible wavelengths of light that provide a blue visual sensation, like the blue sky. Others aspects that must be considered are how bright the light is, how far away, how long you're exposed and when you're exposed to the light. Also, we are more likely to sleep soundly in the wee hours of the morning, when our body temperature is lowest, and most likely to awaken when our body temperature starts to rise, usually between 6 AM and 8 AM. As we age, the brain's "pacemaker" loses cells, changing circadian rhythms, especially sleep patterns. The elderly may nap more frequently, have disrupted sleep, or awaken earlier.

RESETTING THE CLOCK:The RPI researchers developed a method for resetting the internal master clock in studies of both teens and the elderly. The scheme removes blue light at certain times (depending on how one wants to reset the clock) by wearing orange glasses, followed by exposure to blue light and darkness at nighttime. The key is a distinct, repeated pattern of light and dark.

SLEEP STAGES:

• Stage 1: drowsiness
• Stage 2: light sleep
• Stages 3 and 4: deep sleep
• Stage 5: Rapid-eye movement (REM) sleep. REM is when people dream, perhaps because the brain is more active and the muscles are relaxed. These five stages occur cyclically; a person may complete five cycles in a typical night's sleep

If you would like more information, please contact:

Lighting Research Center
Rensselaer Polytechnic Institute
21 Union St.
Troy, NY 12180 USA
(518) 687-7100
http://www.lrc.rpi.edu
cimom@rpi.edu

ON THE WEB:

RPI: www.lrc.rpi.edu

American Academy of Sleep Medicine: www.aasmnet.org