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Dear Mayo Clinic: Once daylight saving time ends, I find it difficult as it gets darker earlier. I also notice that I get a bit more depressed in the winter.

My friend suggested a light box for seasonal affective disorder. What is a light box, and can it be helpful in improving my mood?

A: Seasonal affective disorder, or SAD, is a type of depression that typically occurs each year during fall and winter. If you’re like most people with SAD, your symptoms start in the fall and continue into the winter months, sapping your energy and making you feel moody.

It is important not to brush off that yearly feeling as simply a case of the “winter blues” or a seasonal funk you must tough out on your own. Take steps to keep your mood and motivation steady throughout the year.

The use of light therapy can offer relief. For some people, light therapy may be more effective when combined with another SAD treatment, such as an antidepressant or psychological counseling, or psychotherapy.

Light therapy boxes for SAD treatment are also known as light boxes, bright light therapy boxes and phototherapy boxes. Light boxes come in different shapes and sizes. Some look like upright lamps, while others are small and rectangular.

All are designed to do the same thing, but one type may work better for you than another.

A light therapy box mimics outdoor light. Researchers believe this type of light causes a chemical change in the brain that lifts your mood and eases other symptoms of SAD.

How to use a light box

Generally, the light box should provide an exposure to 10,000 lux of light and emit as little ultraviolet, or UV, light as possible.

Typical recommendations include using the light box:

• within the first hour of waking up in the morning,
• for about 20 to 30 minutes,
• at a distance of about 16 to 24 inches from the face, and
• with eyes open but not looking directly at the light.

Light boxes are designed to be safe and effective, but they aren’t approved or regulated by the Food and Drug Administration for SAD treatment, so you can buy a light box without a prescription.

Still, it’s best to talk with your healthcare provider about choosing and using a light therapy box. Most health insurance plans do not cover the cost.

A caveat: If you’re experiencing both SAD and bipolar disorder, the advisability and timing of using a light box should be carefully reviewed with your healthcare provider. Increasing exposure too fast or using the light box for too long each time may induce manic symptoms if you have bipolar disorder.

If you have past or current eye problems, such as glaucoma, cataracts or eye damage from diabetes, get advice from your eye care provider before starting light therapy.

How to choose a light box

Here are some questions to think about when buying a light box for SAD:

Is it made specifically to treat SAD? If not, it may not help your depression. Some light therapy lamps are designed for skin disorders, not for SAD. Lamps used for skin disorders primarily emit UV light and could damage your eyes if used incorrectly.

How bright is it? Light boxes produce different intensities of light. Brighter boxes will achieve the same effect as dimmer boxes with less use each day. Typically, the recommended intensity of light is 10,000 lux.

How much UV light does it release? Light boxes for SAD should be designed to filter out most or all UV light. Contact the manufacturer for safety information if you have questions.

Can it cause eye damage? Some light boxes include features designed to protect the eyes. Ask your eye care provider for advice on choosing a light box if you have eye problems, such as glaucoma, cataracts or eye damage from diabetes.

Can you put it in the right location? Think about where you’ll want to place your light box and what you might do during its use, such as reading. Check the manufacturer’s instructions so you receive the right amount of light at the proper distance.

Again, talk to your healthcare professional about light box options and recommendations to get one best suited to your needs.

— Compiled by Mayo Clinic staff

Mayo Clinic Q & A is an educational resource and doesn’t replace regular medical care. Email MayoClinicQ&A@mayo.edu. For more information, visit mayoclinic.org.

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