Light Therapy

The short version: Light therapy can treat seasonal affective disorder (eg winter depression) and sometimes regular depression. Buy this light box, and at some time between 6 AM and 9 AM, sit exactly 12 inches away from it and do some activity that doesn’t involve staring directly at the light box. Continue every morning for the period of time you’re at risk of depression. If bipolar, don’t try this without medical supervision.

The long version:

1. Why does light therapy work?

The most important effect of light therapy is coordinating your circadian rhythm.

The circadian rhythm is the body’s 24-hour cycle, which coordinates physiological processes like sleeping, waking, digestion, hormone release, etc. The rhythm is set by the suprachiasmatic nucleus of the hypothalamus (aka the “body clock”), but it is not actually very good at this and on its own is likely to mess up by about an hour a day. In order to calibrate itself, it relies on external cues – most importantly sunrise and sunset times, but also social cues like going to work, eating meals, et cetera.

When the circadian clock is confused, bodily functions tend to happen in a poorly-choreographed way. For example, your system may not be entirely sure whether it’s time to sleep or time to be awake, and so you may be about equally tired all the time, never quite drowsy enough to sleep well at night or awake enough to do your best work during the day. We don’t understand exactly how many bodily systems rely on the circadian clock or what problems happen when they’re poorly choreographed, but we know that depression can be both a cause and an effect of circadian dysfunction.

Humans evolved in Africa where the days are mostly the same length throughout the year, and our circadian clocks are not really prepared for northern latitudes where the days are very short in winter and very long in summer. Seasonal extremes violate their basic calibrating assumption: that morning will precede evening by about twelve hours. Most people’s circadian clocks are able to limp on despite this. Other people’s will fail in various ways. Some people will have mood episodes in the winter when days are shortest, other people in the summer when they’re longest, and still other people in spring and autumn when the rate of change in the length of daylight is greatest. The most important effect of light therapy is to trick the circadian clock into thinking sunrise is at a normal time, stabilizing these swings.

Normal, non-seasonal depression also seems to involve changes in circadian rhythms, though it’s not entirely clear why. Possibly this is related to a pattern where depressed people seem to underweight output from the external world in favor of mental priors, which might also applied to “zeitgebers” like light and social rhythms. The most typical sign of this is depressed people waking up early and being unable to get back to sleep. Light therapy can help correct this issue and reduce depressive symptoms.

Aside from all this, a secondary effect of light therapy is just to make people happier and more energetic. Almost everyone is happier and more energetic on bright, sunny days, maybe because of an evolutionary program telling animals to be more active during good weather. Light therapy can imitate this effect and help people feel better, regardless of circadian rhythm status.

2. What are the different kinds of light therapy?

The two main kinds of light therapy are light boxes and dawn simulation.

Light boxes are extremely bright lights. They try to trick the circadian clock into believing it’s daytime by simulating one of the most salient features of daytime: sunlight. Normal indoor lights, even very bright indoor lights, are only about 1% as bright as the sun. Light boxes are brighter, around 10% as bright as the sun, and more likely to affect circadian rhythm.

Dawn simulators are lights that slowly shift color and brightness in the same pattern as a natural dawn. They try to trick the circadian clock into believing it’s daytime by mimicking the specific change in light color and intensity associated with sunrise – first red, then yellow, then blue light, increasing in a sigmoidal pattern over an hour or two.

Of the two methods, light boxes are better-studied, but dawn simulators will be more convenient for many people. Of two studies comparing them, one found light boxes were a bit more effective, and the other found dawn simulators were a bit more effective. Either would be an okay choice. If you are indecisive and want me to tell you which one to use, I recommend using light boxes because there’s more data.

3. When should I do light therapy?

You should do light therapy in the morning. Your goal is to de-confuse your circadian clock by giving it a stable and predictable sunrise time every day. If you did light therapy during the afternoon, your circadian clock would already know it was day, and wouldn’t benefit. If you did light therapy at night, your circadian clock would just become even more confused. So the recommended time for light therapy is between 6 and 9 AM.

Although anytime in this range will be “good enough”, some times in this window may be better than others. The absolute best time will be whenever your circadian clock is naturally programmed to expect sunrise. This is kind of unrelated to when the real sunrise is, and more related to whether you are an “early bird” or a “night owl”. If you enjoy being very precise, you can find the exact optimal time for you to do light therapy by taking the Horne-Östberg Morningness-Eveningness Questionnaire. Scroll down on the results page until you find the part where it tells you the optimal time to do light therapy.

If you use a light box, you should start using it at this time. If you use a dawn simulator, you should arrange for its dawn simulation to end at this time.

4. How do I do light therapy with a light box?

Decide on a dose, choose a light box, and sit near the light box at the right distance for the right time to get the dose you want.

–4.1. What dose of light therapy should I start with?

The usual starting dose of light box therapy is 5,000 lux-hours daily.

A lux is a unit of ambient brightness. A bright moonlit night is about 1 lux, a candlelit dinner is about 10 lux, indoor lighting is about 100 lux, a cloudy day is about 1000 lux, a sunny day in the shade is about 10,000 lux, and direct sunlight at noon is about 100,000 lux. These numbers may seem extreme, because our eyes effortlessly adjust to different brightness levels. But the numbers are accurate and your intuitions are wrong – direct sunlight really is a hundred times brighter than even a brightly lit indoor room.

A lux hour is one lux for one hour. So a two-hour candlelit dinner gives you about 20 lux-hours of light; ten hours spent outside on a cloudy day gives you 10,000 lux-hours of light. Since the usual starting regimen of light therapy is 5,000 lux-hours between 6 and 9 AM, you’re not going to be able to do this unless you have at least 1,666 lux, ie enough to get 5,000 lux-hours in three hours.

The usual solution is to get 10,000 lux for half an hour. For most people, this works fine.

–4.2. What is the best brand of light box?

Any brand is fine as long as it provides you the right dose.

Almost every brand claims to be “10,000 lux”. This claim is meaningless. Remember, lux is a unit of ambient brightness, not of the inherent power of a given light source. A 60W light bulb held an inch from your eye is about 20,000 lux. A lighthouse produces 10,000 lux if you’re far enough away from it; a firefly could produces 10,000 lux if it’s right up against your eye.

Reputable lights will give you a brightness and a distance, eg “10,000 lux at a distance of twelve inches”. I cannot stress this point enough. Most light boxes on the market right now are scammers selling perfectly normal light bulbs as “10,000 lux light boxes!”, and it’s completely legal as long as the small print includes “this is only 10,000 lux if you hold it right against your face”. You need to either use a specific, reputable light box endorsed by some kind of psychiatric organization, or a light box that very clearly tells you how close you have to be in order to get 10,000 lux.

The two most informed consumer reviews of light boxes, NYMag Strategist’s and New York Times Wirecutter’s, both recommend as their first choice the Carex Daylight Classic Plus, which costs $150 off Carex’s website and $115 on Amazon. I agree. Carex is a reputable company. The light box has a stand to help you arrange it so the light shines from above (which more effectively mimics sunlight, and so may be helpful). Most important, it gives the distance at which its light box provides 10,000 lux, and that distance is a manageable/comfortable 12 inches. This product is large and bulky, but that’s because it actually tries to deliver on its claims; the many smaller and more convenient light boxes you can find around mostly don’t work.

If you insist on a smaller, cheaper light box, you can use something like this TaoTronics lamp. It says to use it 5.5 – 20 inches from your face, but you will not be getting 10,000 lux unless you use the 5.5 inch distance. Getting a light 5.5 inches from your face is actually very hard, there’s not much room for error, and unless you are willing to contort yourself into the necessary position to make this work you might want to just try light glasses instead (see 4.4 below).

–4.3. How do I use the light box?

Reputable light boxes will either tell you at what distance they are 10,000 lux, or tell you how many lumens they emit; if you know the lumens and your distance, you can use this calculator to calculate how many lux you’re getting. Warning: dose can drop off fast: a light box that gives you 10,000 lux when you’re one foot away will only give you 2500 lux when you’re two feet away. Play around with the lumen calculator until you’re comfortable with the distance and dose you’re receiving.

Once you have a time and a distance, go to that distance at that time and turn on the light box. Do not stare at the light box directly; this will damage your eyes. Just do whatever you would normally be doing, in the much brighter environment of being close to a light box. Since you have to stay a constant distance from a stationary object, you probably won’t be able to do chores or anything like that. You could read, watch TV, do work on the computer, play games on your phone, etc. Keep doing this until you’ve gotten the dose you want, then turn off the light and go about your day normally.

–4.4. What are light glasses?

Light glasses take the lumens*distance = lux relationship to an extreme. Instead of a very bright light a foot away from you, they use moderately bright lights on glasses right next to your eyes, providing the same 10,000 lux that a light box would. They may be more convenient since you can walk around in them; some people use them on their daily commute (although they probably look kind of silly).

In theory these ought to work, since they’re providing the same treatment as light boxes through a different delivery system, but I don’t know of any really strong research demonstrating that they do. Most reviewers recommend the Luminette brand because “it has studies”, though if you look closely these studies are all for random easy-to-detect effects and not for seasonal affective disorder or depression. Competitors include Pocket Sky, Re-Timer, and Ayo. You can find some very comprehensive reviews here.

In short, they’re a cool idea, but caveat emptor.

–4.5. What if I don’t feel better at the standard dose?

Like any other time you don’t improve on a standard dose of medication, you might want to consider raising the dose. You can try going up to 10,000 lux hours, which might mean sitting in a 10,000 lux environment for one hour – or 20,000 lux-hours, which might mean sitting in the environment for two hours.

–4.6. What if I’m sure I have seasonal depression, but no dose of light therapy works for me?

Possibly some people’s circadian clocks are not fooled by 10,000 lux of illumination; they don’t register it as daylight and switch to day mode. This isn’t too surprising; direct sunlight is more like 50,000 to 100,000 lux. Unfortunately, many of the researchers and companies operating in this space are morons and refuse to make light boxes brighter than 10,000 lux. If you’re one of the people with this problem, you have a few options.

You could try sitting closer to your light box. A light box that produces 10,000 lux at one foot should produce 40,000 lux at 6 inches, though this may be uncomfortable and require some contortion to make it work.

You could try buying multiple light boxes. I’ve never heard of people doing this, but in theory it should work, as long as they’re all the right distance from you and facing towards you. Place yourself in the middle of a semicircle made of five light boxes, each of which is giving you 10,000 lux, and you should be getting 50,000 lux, eg daylight levels.

Or if you’re handy, you could try building a very very very bright light. Some people I know have done this and confirmed it worked very well for their severe seasonal depressions unrelieved by standard light boxes. Both have written up their experiences including instructions on how to build replicas of their devices. David Chapman writes about his experience building a 30,000 lumen light which provides 30,000 lux at a distance of two feet (or 120,000 lux at a distance of one foot). More recently, he built this kind of extreme 90,000 lumen lamp, which provides ~25,000 lumen level lighting to a whole room. Eliezer Yudkowsky built another light to treat his partner’s seasonal affective disorder unresponsive to standard light boxes. He doesn’t have a good estimate of how many lux it provided but it must have been more than 10,000; you can see the schematics here.

The SKY PORTAL is a light-box-like product capable of producing 60,000 lux at standard-light-box-distance, and may also mimic the color spectrum of sunlight better than other products, but it costs $1100 and is made by an individual who could best be described as “eccentric”.

–4.7. Are light boxes safe? What if they damage my retina or something?

No light box is as bright as being outside on a sunny day. If you don’t expect side effects from going outside in summer, you probably shouldn’t expect them from a light box.

Of course, you wouldn’t stare directly at the sun on a sunny day, and you shouldn’t stare directly at a light box either.

Anybody with eye problems that make it dangerous for them to go outside on a sunny day shouldn’t use a light box without talking to their ophthalmologist.

Any light box with a spectrum different from normal daylight might potentially be more dangerous than going outside on a sunny day. I haven’t really seen any evidence of this, but I guess it’s something you could be concerned about.

Any light box that emitted ultraviolet light in quantities greater than the sun could potentially be dangerous, but the sun emits really quite a lot of ultraviolet light and I’ve never heard of any light box actually causing this problem.

Light boxes might make bipolar people manic. This isn’t a violation of the above principle – bright sunlight can also make bipolar people manic if they get it at a time they’re not expecting. This is why so many people become manic in the spring or autumn (when duration of daylight changes fastest), or when they travel across time zones. Although bipolar people can benefit from light therapy, they should probably talk to a psychiatrist first to make sure they’re protected from manic switch.

5. What are dawn simulators?

Dawn simulators are lights that try to imitate sunrise. Remember, seasonal affective depression occurs when your circadian clock gets confused because it can’t parse unusual day lengths. Light boxes help by delivering a strong sign that it is daytime: very bright light. But another strong sign of what time of day it is, is the specific change in light color and intensity associated with dawn – first red, then yellow, then blue light, increasing in a sigmoidal pattern over an hour or two. So one might predict that a light that simulates this pattern would be as effective as light boxes in correcting circadian rhythms – and studies suggest this is true.

One advantage of dawn simulators is that you don’t need to be awake to use them. Just like normal sunrise, the light of dawn simulators can get through your closed eyelids and register with your circadian clock, even when you’re asleep. This can make them more convenient than light boxes, especially if your circadian rhythm’s optimal time for light therapy is before your usual wake-up time. Some people say dawn simulators make unusually gentle and pleasant alarm clocks.

(you can also use them while awake, just like any other light source, but you have to make sure they’re the only thing lighting your room), the New York Times’ Wirecutter, and all agree that Philips HF3520 ($100 on Amazon) is excellent. Put it somewhere nearby when you sleep, set it to the 40 minute dawn simulation program, and have it start 40 minutes before your ideal circadian sunrise time (see part 3) so that it ends exactly on the dot.

6. Can I use a dawn simulator to start, and then a light box once the dawn simulation is complete?

In theory this ought to work very well, but nobody has studied it, and there is no product that automatically combines both functionalities. If you are a light box manufacturer, consider this a feature request.

7. What conditions can I use light therapy for?

Light therapy is most commonly used in winter depression. The bright light or dawn simulation mimics the day length of a non-winter season.

Various studies suggest that light therapy works about as well as antidepressants for regular unipolar depression, and that light therapy taken with antidepressants can make the antidepressants work more quickly. It also helps with bipolar depression, possibly even better than unipolar depression, but it should only be used with your psychiatrist’s approval due to the risk of manic switch.

Although there are few studies demonstrating this in healthy young adults, in theory light therapy ought to be helpful with insomnia, and especially with circadian rhythm disorders.

Various people make all sorts of unsubstantiated claims that it can help with anxiety, obsessive-compulsive disorder, and eating disorders. None of these have really been well-established, although night eating syndrome has a clear circadian component and it would not surprise me at all if light therapy helped.

Some completely healthy people find light therapy helps them feel more awake in the morning and be more productive during the day. Dawn simulators work well as unusually gentle alarm clocks that help your body feel “ready” to wake up, and light boxes are a good way to simulate daylight-like levels of light in an otherwise dark and gloomy room. If you want to get to bed earlier and wake up earlier, “circadian rhythm hacking” like light boxes and dawn simulators might be helpful.

8. How do light boxes and dawn simulators compare to natural sunlight?

Natural sunlight is better. It’s brighter than a light box, and more dawn-like than a dawn simulator.

This is important if you’re using light therapy for something other than seasonal affective disorder. Some people, in the middle of summer, sit by a light box in the morning in order to help with their depression. This could work. But it will work less well than sitting outside in the bright summer sunlight at the same morning hour. Note that you really do have to be outside – just opening a window won’t give you enough lux.

I’m not sure if you could get the same benefit as a dawn simulator just by sleeping facing an open (ie uncurtained) window at the same hour. You could try opening your window and using a dawn simulator and seeing which is brighter. My guess is that this time the open window would work.

9. Can I try this on my own, or do I need a doctor or psychiatrist helping me?

If you’ve read this document, you already know more than 95% of psychiatrists about light therapy. Trust me, I’ve given lectures about this to psychiatrists and they don’t know any of this stuff. You’ll be fine.

The only exception is if you’re bipolar. Any change in circadian rhythm can make bipolar people manic; please ask a psychiatrist to walk you through the process. They may not know much about light therapy, but they can help figure out ways to prevent you from getting manic or to catch incipient mania quickly.