FAQs and Research about Light Therapy

What is Seasonal Affective Disorder, S.A.D.?
SAD (Seasonal Affective Disorder) is a type of winter depression that affects an estimated half a million people every Winter between September and April, in particular during December, January and February.
It is caused by a biochemical imbalance in the hypothalamus due to the shortening of daylight hours and the lack of sunlight in winter.
For many people SAD is a seriously disabling illness, preventing them from functioning normally without continuous medical treatment. For others, it is a mild but debilitating condition causing discomfort but not severe suffering. We call this subsyndromal SAD or 'winter blues.'

There is another subtype called Summer-SAD, which occurs in the spring & summer months. Summer-SAD is much rarer than Winter-SAD, is less well researched, and its cause is undetermined. Throughout this website, unless otherwise noted, the term "SAD" refers specifically to Winter-SAD. The two share a distinct link between changes in natural light and seasonal depression.
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What is Lux? How much Lux is recommended?
A great deal of research and study has been conducted about bright light treatment and light therapy to determine what type of light, the time of day and how much light yielded will produce the most effective response. This is known as the dose response relationship, or in layman’s terms Light therapy involves the use of a special type of light fixture that produces much brighter light than regular indoor lighting. The intensity of the light is given in lux. Lux is measured at a specific distance away from a light source; for light therapy devices, this specific distance is at the user's eyes. Because light diminishes with distance, light box intensity ratings should always be given at a specific distance from the unit.

Lux is not the same as lumens. Lumens refer to the amount of light generated by a bulb at its surface. Since light intensity decreases exponentially with distance from the light source, knowing the number of lumens a light bulb gives off doesn't help you in determining at what distance you'll receive a particular amount of lux, especially since other factors— such as the positioning of the bulbs in relation to each other within the fixture, whether it is covered by any kind of diffuser, and the reflectivity of the surface behind the bulbs— can affect the light output of any fixture.

The standard light intensity in the industry,recommended by researchers and clinicians, is 10,000 lux at a specified distance. This is an amount significantly higher than standard indoor lighting.1 Most homes have light levels between 100-300 lux, while well-lit offices generally don't go above 700 lux. While daylight is almost always at least 10,000 lux (on a clear spring morning, around 10,000 lux; at noon in the height of summer, over 100,000 lux), natural sunlight levels are often unpredictable due to weather, latitude or terrain, and may not be available at the times required (either early morning or evening).2 Therefore, the purchase of an appropriate device is recommended for those undergoing bright light treatment.3

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What about BLUE LIGHT?
Dr. Norman Rosenthal in his 2005 revision of "Winter Blues" states,"The bottom-line answer is, at this time stay with conventional white-light fixtures. We have decades of experience indicating that these are effective and safe. As of the writing of this book, there is not one published study on the effectiveness of blue light for treating SAD. Nor is there the long track record of safety. On the contrary, there is long-standing concern about potential toxicity of blue light to the eyes."                                                                                                                                              Back to top
What is the most appropriate Light Box?
The best lights for bright light therapy are metal fixtures containing white fluorescent light bulbs behind a diffuser, and tilted forward so that the light is angled downward, permitting more light to enter the eyes and decreasing the apparent brightness of the light, in turn creating less glare and improving user comfort.4 The diffuser performs two purposes: it spreads the light evenly over the surface of the unit, and it absorbs and filters out the potentially harmful UV rays.5 A variety of light boxes are available to meet individual needs, including large models on floor stands for use with exercise equipment, very compact models for frequent travel, and even models designed to fit into standard office decor.

While the critical factor in bright light treatment with a light box is the intensity of the light, full spectrum light with the UV-A and UV-B filtered out for eye and skin safety produces less glare than other types of lighting, resulting in greater user comfort.6, 7, 8, 9                                                                                                                                              Back to top
Side Effects
Bright light treatment is generally well tolerated by most people. Side effects, when they do occur, are almost always transient and mild, and only a very small percentage of people who try bright light treatment need to discontinue it due to troublesome side effects.18

For those who experience initial side effects, there are two easy ways to reduce them while allowing your body to acclimate to the light therapy: either move a few inches further away from the light source and gradually, over several days to two weeks, move closer until you are at the correct distance to receive 10,000 lux of light, or reduce your treatment time (to 15 minutes instead of 20-30 per day) initially, and gradually increase your exposure time by a few minutes every few days until you are using it for the amount of time your body requires.19

In the several published clinical studies that examined side effects, the most commonly reported side effects were: headaches, eye strain, nausea, feeling 'wired', and dizziness.20, 21, 22, 23
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Safety
Bright light treatment with a properly constructed fluorescent light box is generally considered to be safe.24, 25, 26 Studies examining the effects of short-term (up to 4 weeks) and long-term (three to ten years) on the eye showed no changes in response to the use of the lights.27

It is well known that ultraviolet (UV) exposure causes damage to the eyes and skin. Numerous sources warn of the danger of excessive UV exposure from improperly constructed light boxes that do not eliminate the UV wavelengths. One of these sources cautions that UV levels in fluorescent light fixtures without appropriate diffusers to eliminate them could reach toxic levels in twenty years of daily use during the winter.28 Therefore, it is very important that any light device being used for bright light therapy be free of UV wavelengths. Any manufacturer that you consider purchasing a light box from should be able to provide independent laboratory verification that their light boxes are UV free.

While light treatment appears to be safe for most people, researchers warn that certain people should be carefully monitored when using light treatment. People who have preexisting eye abnormalities (for example, macular degeneration or retinitis pigmentosa), those with systemic illnesses that affect the retina (diabetes mellitus, systemic lupus erythematosis), those who have had cataract surgery, and those taking certain photosensitizing medications (including tetracyclines, sulfonamides, psoralens, and some antidepressants and neuroleptics) should begin light treatment only with routine ophthalmologic examinations and with careful consideration of the risks and benefits.29, 30                                                                                                                                              Back to top

1 Rosenthal, NE: Winter Blues: Seasonal Affective Disorder - What It Is and How to Overcome It. (rev. ed.) New York: Guilford Press, 1998, p 239.

2 ibid, pp 108 & 138-139.

3 Kripke, DF & RT Loving: Bringing therapy to light. Sleep Rev. Winter 2001.

4 Rosenthal, 1998, p 107.

5 ibid, p 108.

6 ibid, pp 108, 110 & 117.

7 Berman, SM & DL Jewett: Full vision photometry for the computer workplace based on physiological and behavioral principles. Conference Paper presented at a symposium of the CIE (International Commission on Illumination). Undated.

8 Berman, S: The coming revolution in lighting practice. Energy User News. 25(10), 2000.

9 Brainard, GC, NE Rosenthal, D Sherry et al.: Effects of different wavelengths in seasonal affective disorders. J Affect Disord. 20, pp 209-216, 1990.

20 Lam, p 74.

21 Kogan, AO & PM Guilford: Side effects of short-term 10,000-lux light therapy. Am J Psychiatry, 155(2), pp 293-294, 1998.

22 Labbate, LA, B Lafer, A Thibault et al.: Side effects induced by bright light treatment for seasonal affective disorder. J Clin Psychiatr, 55(5), pp 189-191, 1994.

23 Levitt, AJ, RT Joffe, DE Moul et al.: Side effects of light therapy in seasonal affective disorder. J Clin Psychiatry, 150(4): pp 650-652, 1993.

24 Lam, p 74.

25 Rosenthal, p 122.

26 Gallin, PF, M Terman, CE Remé et al.: Ophthalmologic examination of patients with seasonal affective disorder, before and after bright light therapy. Am J Ophthalmol, 119, pp 202-210, 1995.

27 ibid.

28 Lam, p 73.

29 ibid.

30 Remé, CE, C Grimm, F Hafezi et al.: Lamp standards and ocular safety. In: Seasonal Affective Disorder. Practice and Research. Edited by Partonen, T & A Magnusson. New York: Oxford University Press, 2001, pp 79-83.

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