“I try to focus on helping others,” Pataki said. “It gives me purpose.”

People with SAD typically have episodes of depression that begin in the fall and subside in the spring or summer. The return to standard time, which is happening this weekend, can be a trigger for SAD. A milder form, subsyndromal SAD, is recognized by medical experts, and there is also a summer variety of seasonal depression, although less is known about it.

In 1984, a team led by Dr. Norman Rosenthal, then a researcher at the National Institutes of Health, first described SAD and coined the term. “I believe because it’s easy to remember, the acronym stuck,” he said.

Scientists are learning how specialized cells in our eyes transform the blue part of the light spectrum into neural signals affecting mood and alertness.

Sunlight is loaded with blue light, so when cells absorb it, the alertness centers of our brain are activated and we feel more awake and perhaps even happier.

Researcher Kathryn Roecklein of the University of Pittsburgh tested people with and without SAD to see how their eyes reacted to blue light. As a group, people with SAD were less sensitive to blue light than others, especially during the winter months. This suggests a cause of winter depression.

“In winter, when light levels drop, this, combined with lower sensitivity, may be too low for healthy functioning, leading to depression,” Roecklein said.

Miriam Cherry, 50, of Larchmont, New York, said she spent the summer planning how she would deal with her winter depression. “It’s like clockwork,” Cherry said. “The sunlight is weak. The day ends at 4:45 p.m., and suddenly my mood is horrible.

Many people with SAD respond to light therapy, said Dr. Paul Desan of the Winter Depression Research Clinic at Yale University.

“The first thing to try is light,” Desan said. “When we expose patients to bright light for about half an hour each morning, the majority of patients improve significantly. We don’t even need medicine.

The therapy involves devices that emit light about 20 times brighter than regular indoor light.

Research supports using light of around 10,000 lux, a measure of brightness. You should use it for 30 minutes every morning, according to research. Desan said it can help not only people with SAD, but also those with less severe winter problems.

Specialty lights cost between $70 and $400. Some products marketed for SAD are too weak to do much good, Desan said.

Yale has tested products and offers a list of recommendations, and the nonprofit Center for Environmental Therapeutics offers a consumer guide to selecting a lamp.

If your doctor has diagnosed you with SAD, check with your insurance company to see if the cost of a light might be covered, Desan suggested.

Antidepressants constitute a first-line treatment for SAD, along with light therapy. Doctors also recommend maintaining a regular sleep schedule and walking outside, even on cloudy days.

The benefits of light therapy may wear off when people stop using it. Studies have shown that one type of talk therapy — cognitive behavioral therapy, or CBT — has longer-lasting effects, said Kelly Rohan, a researcher at the University of Vermont.

CBT involves working with a therapist to identify and change unhelpful thoughts.

“A very common thought among people is ‘I hate winter,’” Rohan said. “Reframe it to something as simple as: ‘I prefer summer to winter,'” she suggested. “It’s a factual statement, but it has a neutral effect on mood.”

Working with a therapist can help people take small steps toward having fun again, Rohan said. Try planning undemanding but enjoyable activities to come out of hibernation mode, which “could be as simple as meeting a friend for coffee,” Rohan said.

People with SAD have six months to create coping strategies, and some have found tips that work for them — even though scientific support may be limited.

Elizabeth Wescott, 69, of Folsom, Calif., thinks contrast showers help her. This is an aquatic therapy borrowed from sports medicine which consists of alternating hot and cold water during the shower. She also uses a light box and takes an antidepressant.

“I’m always looking for new tools,” Wescott said.

Cherry, in New York, devotes a corner of her garden to the first blooming flowers: snowdrops, winter aconite and hellebores. These flower from February.

“This is going to be a sign to me that this isn’t going to last forever,” Cherry said. “It will get better and spring is coming.”

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Education Media Group. The AP is solely responsible for all content.