Light therapy is the use of bright light to adjust the circadian rhythm, elevate mood, and help people sleep better. A synchronizing agent like melatonin, light therapy helps adjust the body’s clock. It is therefore useful in addressing circadian disorders such as
Also called photoperiod phototherapy or bright light therapy, this treatment has the benefits of being inexpensive (after an initial investment in equipment and possibly training) and causing few side effects. Light therapy is most often given through a light box or light table, which is kept in a person’s home. Night owls use the light box in the morning and morning larks use it at night to affect their circadian cycles,
Light activates the suprachiasmatic nucleus in the brain’s hypothalamus. This is the brain’s main clock and helps the body’s circadian rthym synchronize with natural daylight. The regular exposure to sunlight helps pin down the body clock. This is through to be a large part of the reason Seasonal Affective Disorder strikes many during the time of the year with short daylight hours.
Four factors are important in light therapy:
- spectral quality (similar to daylight white)
- brightness (overcast day = 10,000 lux, vs. indoors = 300 lux)
- time of day of exposure
- length of exposure
It has been found that the most effective list is white light tinged with blue. The person’s prior recent exposure to light affects how well phototherapy works, too. If the subject has been outdoors during the daytime, the artificial light won’t be as effective as a it is when the subject has been indoors.
When phototherapy works, it modifies not only the timing of sleep, but all the other physiological markers that accompany sleep. Measurement of body temperature, cortisol levels, blood pressure, etc. all show the same patterns they normally show during sleep. The phototherapy has had a chronobiotic effect and shifted the body in time.
Other uses of light therapy include the treatment of skin conditions, and the connection between sunlight and health has been part of folk medicine for centuries. This folk understanding has been partly vindicated by the discovery that sun exposure can precipitate production of Vitamin D in the skin and many scientists suspect sunlight has other health benefits.
Although going outdoors during daylight is the easiest way to get exposure to bright light, it is not always practical and sometimes the person needs the bright light when it is dark outside. Medical upply stores sell light tables that generate high intensity light in a small space. Having the person sit near the light for a period of time (typically under an hour) is usually recommended.
Commercial light tables are available that generate 10,000 lux. (Lux is a unit of light intensity.) By contrast, a typical home has interior lighting of 50 to 80 lux, and direct sunlight outdoors runs from 10,000 to 100,000 lux. One common regimen is for the person to be near the light table for 30 minutes in the morning. During this time, other indoor activities such as watching television, using the computer, cooking, shaving, etc. can be done. Light tables are marketed to people with Seasonal Affective Disorder and those who travel frequently and seek to overcome jetlag. They are typically portable – easy to carry and less than 18 inches across. You don’t want one that is too small, as you need your eyes to be exposed to the light. White light has also been shown to be superior to blue light tables when it comes to treating circadian disorders. And make sure the table does not emit too much harmful ultraviolet light, which people use to tan but which can harm the skin. Some tables have filters to keep out the UV light. The overall intensity of the light is not high enough to do damage, except in a few people with eye diseases, and the exclusion of UV light makes it even safer than daylight. Formal study has shown that people who are not seeing improvement with light therapy should try increasing the length of exposure rather than the intensity of the light.
A British study unfortunately found no improvement in circadian disorder symptoms in people with Chronic Fatigue Syndrome.
A Dutch study of light therapy in elderly patients with dementia showed the therapy was not only effective in correcting circadian disorders, but also in preventing depression. This should not be surprising given the co-morbidity of sleep disorders and both depression and dementia.
Can you develop a tolerance for light therapy? The human body often develops tolerance for drugs. The drugs work as intended at first but over time decline in efficacy and higher doses may be required. If light therapy or simple deliberate exposure to daytime sunshine works in the short-run, might it wear off in effectiveness, too? As far as we know, there are no studies on this topic.
Scientists at Flinders University in Australia recently developed eyewear that are worn like glasses and shine light to adjust the wearer’s circadian cycle. The developers hope this device can be used to help people with jet lag.