Seasonal Affective Disorder (SAD) presents one of the most important applications of light therapy. There's a substantial body of scientific evidence supporting the effectiveness of light therapy for SAD treatment. However, the exact mechanisms of how light treatment works are still not entirely understood.
Our daily rhythms are significantly influenced by the presence or absence of natural sunlight. Many of us spend our days in artificially lit indoor environments, which often lack the intensity of natural light required to influence the hormonal systems that regulate our bodily rhythms. Light intensity is measured in lux, and natural sunlight has a considerable intensity, with bright sunny afternoons reaching up to 100,000 lux. Even on the cloudiest days, you can expect around 10,000 lux. In contrast, indoor lighting in homes and workplaces typically remains below 500 lux. Research indicates that at least 2,500 lux of light is needed to suppress melatonin production in humans, a crucial hormone for sleep regulation. Most bright light therapy utilizes 5,000 to 10,000 lux light. "Mal-illumination," or inadequate indoor lighting, is believed to be a contributor to common issues like fatigue, depression, skin problems, weakened immune function, and, of course, sleep disorders.
Light therapy for Seasonal Affective Disorders and circadian rhythm disturbances aims to deliver visible light through the eyes, reaching and stimulating the pineal gland.
Various forms of light therapy are in use today, with natural sunlight being the original source. The sun provides full-spectrum light, encompassing all wavelengths from infrared to ultraviolet. In many cases, light therapy involves the use of equipment that emits either full-spectrum or bright white light.
The goal of light therapy is to increase our exposure to light beyond what we receive naturally. Bright light therapy typically involves gazing at specialized broad-spectrum lights for periods ranging from half an hour to three hours each day, typically during the early morning. It's crucial not to stare directly into the lights to avoid potential eye damage.
The quantity of light matters, and the distance between the lights and your eyes should be carefully monitored. It should be close enough to provide the right amount of light but far enough to safeguard your eyes.
By the mid-1980s, bright-light therapy, or phototherapy, had become the preferred treatment for SAD. However, the four-hour daily commitment proved challenging for many. Researchers conducted additional studies to determine the most effective light therapy regimen. They found that significant benefits could be achieved with a morning-only therapy, halving the required time. Further reductions in therapy time were achieved by increasing the light's brightness or intensity.
With brighter lights, such as 10,000-lux light, effective SAD relief was achieved with just 30 minutes of daily exposure. Symptoms of SAD typically begin to improve approximately a week after the initiation of phototherapy but may return shortly after discontinuation. As a result, experts recommend that individuals with SAD engage in daily bright light exposure from October through April.