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What's a Zeitgeber?

© Stephen Weistling

If you didn’t have a clock, how would you know when to go to sleep, wake up, or eat? You would use something else to keep track of the time of the day. When it got light in the morning, you’d get up. When your cat cried at the refrigerator, you’d know its time to feed her. The heat of the day may trigger responses such as hunger, energy, or the need for a nap. In these cases, light, heat, and even the cat could be an external time cue, or a zeitgeber. The term is German, meaning “time giver” and is commonly used by academics and researchers of circadian rhythms. The most common zeitgeber is daylight.

How does this all relate to shiftworkers? Our biological clocks strongly respond to light and dark. This may be why some night workers find it really difficult to sleep during the day, especially in a room that is not dark enough. Researchers have found that it is possible to “fool” the biological clock by using artificial light, but the experiments only seem to work when the light and dark cycles actually approximate the intensity of actual sunlight or night darkness.

Last month, I spent a night in a motel that had blackout shades on the windows. My wife and I went to sleep at our normal time. However, because the room was so dark, we overslept by an hour and a half. Researchers have found that our eyes, even when we’re sleeping will respond to light, and signal our brains which house the mechanism for the biological clock to start the processes that normally respond to waking up and beginning the day.

Here are two concepts to keep in mind for shiftworkers. One is the worker’s responsibility, and one is the employer’s.

If you are a night worker and must sleep during the day, invest in ways to make your bedroom as much like it is at night. Get blackout shades, and keep the temperature in the room as close as possible to what it would be at night. There’s one zeitgeber that’s really hard to isolate. Noise. You will find it very difficult to approximate the lack of noise you experience at night, but some people use earplugs, or have a fan or other device that provided “background” or “white” noise to filter out the harsher sounds from outside your room.

The second concept is for your employer to install lighting systems at work that approximate a day-like atmosphere in the workplace. In the control room I used to work in, it was possible to light up the area to resemble the middle of the day – outside. Of course this was so bright, we’d turn some of the lights off. What should be done is measure the lumens of light in the area during the day, and then turn on a sufficient number of lights to match that. Many companies find that doing this leads to less fatigue, more alertness, and fewer safety problems. Your company’s Industrial Hygiene department can help with the measurements and other suggestions.

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