Thursday, September 17, 2020

Light Therapy

How to Select a Light Box

In the best of all possible worlds, every light box on the market should have undergone clinical trials to show its efficacy, and should provide customers with accurate technical information about the lamp’s characteristics (illuminance, spectrum, UV filter, etc). In the early days of light therapy, several companies did in fact develop first-generation light boxes together with the researchers, thus optimizing output and standardizing quality. With the success of the field, however, there was an explosion of new manufacturers, and it became sufficient for sales that light boxes merely fulfilled electrical standards. There was little collaboration with scientists to test new light box designs, and most often claims for efficacy and ocular safety were not based on any trials at all. It has become a “me-too” industry, with light boxes more a life-style device than a medical one. This is indeed a difficult situation for practitioners and patients alike.

The CET Board of Directors and Advisors have developed a list of light box criteria. We need to observe certain standards to guide patients, doctors, and insurance companies. The CET Shop offers a specific device designed to the standards of clinical trials. A commission on sales helps to support our website.

Criteria for a light therapy device

The major factors to be considered are clinical efficacy, ocular and dermatologic safety, and visual comfort. Here is a checklist with recommended criteria for light box selection:

  • INTENSITY: 10,000 lux illumination at a comfortable sitting distance. Many lamps attain this intensity only close up (for example, with eyes as close as 5 inches, or 13cm from the screen). Otherwise the glare can be overwhelming, forcing the user to look to the side, with illuminance reduced below the therapeutic range. Check the distance suggested carefully. Ask the manufacturer for calibration data, and whether a broad-field illuminometer was used.
  • PRODUCT SPECIFICATIONS: Check if technical information is absent
  • UV FILTER: Fluorescent lamps should be fitted with a diffusing screen that filters ultraviolet (UV) rays that are harmful to the eyes and skin. Claims of UV protection are common, but questionable if a polycarbonate filter was not used.
  • SPECTRUM: White light is preferable. “Full spectrum” lamps and blue (or bluish) lamps with color temperature above 5000 Kelvin are not superior in efficacy.
  • ANGLE OF GAZE: The individual sits at a desk, usually looking down at reading matter or looking straight ahead. To avoid visual glare from the bright light, the lamp should project downward towards the eyes at an angle.
  • SIZE OF LIT AREA: even though a small light box seems elegant and transportable, even small head movements diminish the wished-for therapeutic dose of light to the eyes.

Bright Light Exposure Risks

Cautionary Notes About Bright Light Exposure

Light energy can interact with and damage skin and eye tissues, especially when a photosensitizing molecule—whether from a drug or produced by the body—is bound within those tissues. The highest risk (for damage to the skin, and cornea and lens of the eyes) is from invisible, short-wavelength ultraviolet (UV) light, which has been filtered out of CET’s recommended light therapy system.

Long-term exposure to intense visible light in the blue range adjacent to the UV range may also pose a hazard to retinal photoreceptors and the pigment epithelium, which takes part in the photoreceptor renewal process. Above age 50, there is concern about blue-light exacerbation of age-related macular degeneration. Although some blue is an important component of white light exposure, lamps with relatively less blue (for example, soft-white fluorescents with color temperatures in the range of 3000-4000 Kelvin) should be favored over cool-white, daylight, or “full spectrum” lamps (5000 Kelvin and higher).

Pre-Existing Medical Conditions May Enhance Exposure Risks

There are certain pre-existing medical conditions of eyes and skin (retinal dystrophies, age-related macular degeneration, porphyria, lupus erythematodes, chronic actinic dermatitis and solar urticaria) that also can show photosensitized reactions to intense visible light. In such cases, bright light therapy should be administered only under guidance of an ophthalmologist or dermatologist, as indicated. Ophthalmologists should keep in mind that in some genetic retinal diseases the eyes are especially light sensitive.

Medications & Enhanced Exposure Risks

Certain medications are known to photosensitize skin and/or retinal tissues. Examples in the visible range of light include psychiatric neuroleptic drugs (e.g., phenothiazine), psoralen drugs, antiarrhythmic drugs (e.g., amiodarone), antimalarial and antirheumatic drugs, porphyrin drugs used in photodynamic treatment of skin diseases, and St. John’s Wort (hypericum). Bright light therapy should not be used concurrently with these drugs. Melatonin can be used in conjunction with light therapy at opposite times of day (usually, evening and morning, respectively), but if used concurrently, it can cause photosensitization.

Drugs that photosensitize primarily in the invisible UVA range (just below the blue range) may also have a “tail” of light absorption that extends into the lower visible blue light range, which could cause photosensitization. Examples are tetracycline, diuretic drugs (e.g., hydrochlorothiazide), sulfonamide drugs and tricyclic antidepressants (e.g., imipramine, nortriptyline, desipramine, amitriptyline). If such a reaction is experienced or suspected, bright light therapy should be discontinued unless substitute medication is available, or it can be administered with protective measures under medical supervision.

Preexisting retinal diseases potentially contraindicated for light therapy:

  • Inherited retinal degenerations
  • Age related maculopathy
  • Diabetic retinopathy
  • Inflammatory chorio-retinal diseases, which comprise a large group of different diseases:
    • Retinal vasculitis
    • Viral, fungal, mycotic, spirochaetal infections
    • HIV-related retinitis
    • Vogt-Koyanagi-Harada disease
    • Sarcoidosis
    • Morbus Becet
    • Acute inflammation of the pigment epithelium

In Conclusion

For the practice of bright light therapy, we must therefore consider the wavelength range of the light (and with that, its energy range) and the absorbing tissues in the eye. For normal healthy eyes, the exposure to bright white light is a physiological situation and does not inflict any overt damage to the skin, visual cells and pigment epithelium. There are, however, certain important caveats:

  • Medications that can enter the skin or retina and that absorb light in the visible range. This might cause photosensitization with subsequent absorption of “too many photons,” leading to damage. If you want to use bright light therapy but are questioning your medication, consult an ophthalmologist or dermatologist.
  • Certain inherited dystrophies of the retina that alter the visual pigments and can render the retina especially sensitive to visible light. If you suffer from an inherited retinal dystrophy and want to use bright light therapy, consult an ophthalmologist.
  • Age–related or other macular degenerations. For age–related macular degeneration, genetic factors increase the risk of disease by about 50%. Patients with such risk factors, or those with several family members suffering macular degeneration, should consult an ophthalmologist before using bright light therapy.
  • Young eyes up to an age of about 30–40 years transmit much more light to the retina than older eyes. Thus, young eyes receive generally higher light doses than older ones.


Vincent DeLeo, M.D., St. Luke’s-Roosevelt Medical Center, New York; Charlotte Remé, M.D., University of Zurich, Switzerland.

Additional Reading

Light Therapy for Mood and Sleep

Light Therapy for Beginners: Six Steps

A Game Changer in the Treatment of Depression

Bright Light Therapy

DSPD (Delayed Sleep Phase Disorder)

Light Therapy for Other Problems

Spotlight on Parkinson’s Disease

A New Way to Help People with Fibromyalgia?

The Light Box CET Recommends

Our Recommended Light Box


theresa with light box
Light boxes that meet certain criteria, such as the BOXelite OS shown here, can relieve symptoms of SAD.

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