Chapter 7
Side Effects of Bright Light

They say that everything good is either risky, immoral, or fattening.  Light treatment is neither immoral nor fattening, but unfortunately, it does have risks that you should know about. To put this in perspective, water has risks, sugar has risks, salt has risks, apples and oranges and sirloin steak have risks, sunlight has risks, and artificial light treatments have risks also. It takes some judgment to know how much is too much – of water, sugar, salt, or indeed, of light.

7.A.  The risk of mania

All effective antidepressant treatments, including bright light, can trigger mania. Manias triggered by bright light can be serious, and perhaps constitute the most important risk of bright light treatment.

What is mania? Mania is a specific unusual mood in which a person becomes too happy, too euphoric, too irritable or too hyper, in a way which causes trouble. Manic people suffer from rapid speech, they talk too much (they feel pressure to keep speaking), and they have too many ideas, causing difficulty concentrating. They are distractible and often jump from one idea to another. They are hyperactive, and often awaken early or cannot sleep. A person who is manic is not the person’s usual self. Sometimes manics venture into things with a high probability of getting hurt physically or socially or suffering financial losses.

Although mania may resemble happiness, cheerfulness, or high energy, in its extreme form, mania is quite risky for the manic person and for the people around. Let me give you some examples of the poor judgment manics show. A manic patient was driving 80 mph down the freeway, and when stopped by a highway patrol officer, he started a fight. He was lucky that the patrolman only beat him up a little. Another patient, a conservative middle-aged mother of several children, became manic enough to go down to the red-light district and solicit male customers. An impoverished patient bought two Cadillacs in one day, though he couldn’t afford a new car at all. Another manic patient on pension ordered a private jet, asking the company to paint it custom yellow for him. A manic patient left his wife and drove a thousand miles, got up in the middle of the night, took off all his clothes and ran around a motel parking lot. A manic patient threatened the life of the President, so the Secret Service considered arresting him. You wouldn’t want all the trouble that mania causes for people and their families.

Mania occurs in people with bipolar disorder, another name for what we used to call manic-depressive illness. The distinguishing feature of bipolar disorder is that a person with this disorder has at least once suffered from mania or at least mild mania (what we call hypomania). Fortunately, I have never heard of severe manic symptoms being triggered by bright light in a person who had not previously suffered from mania. The risk seems to be very low for people who have never had mania. People with bipolar disorder commonly experience periods of depression, when an antidepressant treatment such as bright light might be needed. Indeed, they may suffer more from long depressions than from briefer manias. Bipolar disorder seems to be a biological and genetic illness, just like diabetes, with the peculiar feature that the illness seems to recur and recover, sometimes with little obvious pattern.

When somebody with bipolar disorder is treated with bright light, sudden mania might occur. I know of a patient with bipolar disorder who injured a hospital staff member and needed to be placed in restraints within a few hours after a bright light treatment. Fortunately, this severe kind of reaction to bright light is uncommon except among people with bipolar disorder who have had at least one period of mania in the past, and it seems to be rare if the person is taking a mood stabilizer such as lithium, carbamazapine (Tegretol), or divalproax (Depakote). Most people with bipolar disorder should be taking such a mood stabilizer. Some recent studies suggest that the risk of mania may be no greater with light treatment than with other effective antidepressant treatments, or even less.[80]  Perhaps the risk of mania with light treatment is additional evidence that light treatment can be antidepressant. Nevertheless, if I had ever had a mania, I do not think I would risk bright light treatment unless I were taking a mood stabilizer, and unless I were under close supervision by a doctor.

It is likely that wake therapy also increases the risk of mania.

Mild manic symptoms or irritability have been triggered by bright light in seemingly normal research volunteers and among people who have never had mania. Usually the problem is just poor sleep or feeling a bit angry or feeling a bit hyper. Nevertheless, it is important to recognize these symptoms when bright light produces them, because the dosage of bright light should be immediately reduced or the use of bright light should be discontinued until these symptoms go away. Some people find that they must balance their dosage of bright light: too little light leaves them depressed, but too much may leave them irritable or hyper. Certainly, anybody who is having these symptoms from bright light should immediately discuss them with a doctor.

There is some indication that the risk of mania is greater when bright light is used in the early morning. Possibly, waking up early increases the risk of mania, or possibly the risk comes when the body clock is advanced too early.[81]  Researchers at the National Institute of Mental Health have reported preliminary studies which suggest that when bipolar patients experience switches between mania and depression at least four times a year, bright light treatment is safest in the mid-afternoon.[82]

7.B.  Sunburn and skin cancer

Much as we love the sun, we all know how sunburn hurts. More serious, sunburn and too much sun cause skin cancers, some of which can be fatal. The risk of sunburn and skin cancers such as melanoma seems to be increasing, because air pollution is reducing the layer of atmospheric ozone which normally shields us from most of the sun’s ultraviolet rays. Damage to the ozone layer is allowing the sun to cause more sunburn than sunshine used to cause. People need to get bright light without increasing their risk of sunburn.

Fortunately, you can get plenty of light without sunburn. The benefits of light for depression, the body clock, and sleep, seem to come through the eyes. For good sleep and good mood, there is no need for any sun at all to fall on the skin. From my point of view, long sleeves, long pants, and a hat are just fine for people who want to get their bright light outdoors. Sunscreen may help. There is no persuasive evidence that light hitting the skin is antidepressant.

I have also explained that bright light in the early morning or just before sundown is often the best for the body clock. From the moment the sun rises above the horizon (at least if it is a clear day), the light may be bright enough to do you some good and keep you from wilting. The morning and before-sunset evening times are therefore particularly good times to get outdoors in daylight, possibly even more effective than mid-day for most people, and these times soon after dawn and shortly before sunset give the safest daylight for the skin. Unfortunately, the minute the sun goes below the horizon, the twilight grows too dim to be useful for mood. Oddly enough, the ultraviolet rays which cause sunburn are scattered more by the atmosphere and absorbed more by ozone than are the visible colors of light which make up sunlight. As a consequence, the strong ultraviolet which causes sunburn is mainly a problem when the sun is almost overhead. The greatest risk of sunburn is between 10 am and 3 pm. There is less risk of sunburn before 10 am or after 3 pm. For these reasons, I usually recommend that people try to get most their daylight exposures before 10 am or after 3 pm, except in the winter, if the sun is low even near noon. The risk of sunburn is less important, of course, for those using long sleeves and a hat or sunscreen for protection.

Except in winter, if you would like to get your daylight exposure at mid-day, consider sitting in the shade. Since it is light entering the eyes that is important for your mood, not what falls upon your skin, your eyes can usually be directed towards a sunny part of the environment even when you are sitting in the shade. Also, in most sunny weather (except very dark rainforests), even shade is several thousand lux during mid-day, and therefore the light is helpful.

Most artificial lighting does not contain enough ultraviolet rays to create any risk of bright light treatment, but there are exceptions. Some “full spectrum” bulbs can cause a sun burn if you get very close and if the light does not have a diffuser which filters out the ultraviolet. There is also some ultraviolet produced by the halogen bulbs, but I doubt that much is reflected in the indirect lighting. Purple ultraviolet tanning lights, of course, give off intense ultraviolet light, so you should not look at that light. Some LED lights also give off considerable ultraviolet unless the ultraviolet is shielded.

7.C.  Eye burn

It is true that you can burn the retinas of your eyes by staring at the sun. You should not stare at anything that bright, whether the sun itself or any very bright point of light. As I have mentioned, fluorescents with diffusers spread the light out enough to minimize this risk. Using indirect lighting also eliminates this risk by spreading out the very bright point of light. So far as I know, you can’t do your eyes permanent harm with any of the commercial fluorescent lights or with incandescent lighting used indirectly. It is worth a reminder, nevertheless, that you should not stare at anything so bright that it hurts your eyes. The limit of brightness above which the risks outweigh the benefits is probably around 10,000 lux. Anything much brighter than 10,000 lux is probably unwise. People with special eye problems should ask their eye doctors for further advice about their special problems.

Some doctors have theorized that people taking certain drugs such as major tranquilizers (example: Thorazine) or lithium could hurt their retinas with bright light treatment. Since millions of people have taken these drugs and have gone out into sunlight, I doubt that this risk is more than minor.

There is a kind of light damage to the eyes which might be caused by the ultraviolet rays in ordinary sunlight. It seems that some clouding of the lens and cataracts may be increased by very extensive exposures to the ultraviolet light in outdoor sunshine – the kind of exposure which fishermen experience if they are out on the water every day for much of a lifetime. It seems unlikely that the kind of daylight exposures that I have recommended (only an hour or two a day over the long run) would have any measurable effect on the lenses of the eyes. However, concern about cataract might be another consideration for trying to spend your time outdoors primarily before 10 am or after 3 pm, since most of the ultraviolet reaches us near mid-day.

7.D.  Sleep disturbance risks

With light as with other treatments, there can be too much of a good thing. As we have discussed, bright morning light tends to make us fall asleep earlier and awaken earlier. Thus, bright morning light is the treatment for delayed sleep phase. Conversely, too much morning light can cause the opposite: an unpleasant degree of advanced sleep phase and early awakening. Similarly, although bright evening light is a treatment for advanced sleep phase, too much bright evening light can cause trouble falling asleep and trouble waking up in the morning. Some scientists also think that bright light close to bedtime prevents melatonin from increasing in our blood, as it usually does at that time, and that this may cause trouble with falling asleep. A person using artificial bright light may need to experiment with the timing, duration, and brightness of bright light if sleep problems of these types develop.

7.E.  Headache and eye strain

Some people using artificial bright light treatments have reported temporary headaches or eye strain caused by the light. These symptoms do not seem to be serious or to indicate any permanent injury, but they certainly can be unpleasant. If fluorescent light is being used with 60 cycle flicker, an electronic high-frequency ballast will probably reduce the risk of eye strain. Most people try to reduce the intensity or duration of the light treatment to reduce these symptoms, unless they find that the benefits of the light are greater than the symptoms caused.

7.F.  Suicidal thoughts

In the great majority of cases, bright light treatment (especially in the morning) lifts a person’s mood and increases the person’s energy. Occasionally, however, the effect of antidepressants such as bright light upon a depressed-exhausted person may be to increase energy in a harmful way. There are a couple of cases reported where bright light treatment led to increased suicidal thinking, and at least one suicide has been reported. If the result of bright light treatment is to increase suicidal thinking, it is time to stop the light and time to see a doctor that very same day.

7.G.  Other risks of light

Some other milder side effects of bright light treatment have been reported, but these seem less serious, and I am not certain if they are real. Besides headache and eye strain, nausea, diarrhea, and increased sleep are sometimes associated with bright light treatment. Migraine may be triggered.

Endnote for Chapter 7

80. Benedetti F. Rate of switch from bipolar depression into mania after morning light therapy: A historical review. Psychiatry Res 2018;261:351-6; Sit DK, McGowan J, Wiltrout C, et al.  Adjunctive Bright Light Therapy for Bipolar Depression: A Randomized Double-Blind Placebo-Controlled Trial.  Am J Psychiatry. 2018Link to a website outside this ebook175(2):131-9. [return]

81. Moon JH, Cho CH, Son GH, et al. Advanced Circadian Phase in Mania and Delayed Circadian Phase in Mixed Mania and Depression Returned to Normal after Treatment of Bipolar Disorder.  EBioMedicine. 2016Link to a website outside this ebook;11(Sep):285-95. [return]

82. Leibenluft, E et al.  Light therapy in patients with rapid cycling bipolar disorder: Preliminary results.  Psychopharmacol.Bull. 1995Link to a website outside this ebook;31:705-710; Sit DK, McGowan J, Wiltrout C, et al.  Adjunctive Bright Light Therapy for Bipolar Depression: A Randomized Double-Blind Placebo-Controlled Trial.  Am J Psychiatry. 2018Link to a website outside this ebook175(2):131-9. . [return]