Light therapy is one of those treatments that sounds vaguely wellness-adjacent until you look at the research. Then it becomes one of the better-evidenced interventions in the entire field of mental health and sleep medicine.
It has been used clinically since the early 1980s, is recommended in NHS guidance for Seasonal Affective Disorder, and has a body of randomised controlled trial evidence that would satisfy most sceptics. Whether it works for you specifically depends on what you are using it for and how you use it.
What Is Light Therapy?
Light therapy, also called bright light therapy or phototherapy, involves exposure to a specific intensity and quality of artificial light for a defined period each day. The standard protocol for SAD involves sitting in front of a lamp that produces 10,000 lux of bright white light for 20 to 30 minutes within the first hour of waking.
It is not ultraviolet light. It is not a tanning lamp. It is not infrared. Standard light therapy for SAD is visible white light at high intensity, designed to replicate the light stimulus of a bright outdoor morning. The effect is entirely through the eyes — not through the skin, and not through vitamin D.
How It Works
When bright light enters your eyes in the morning, it activates specialised retinal cells that contain a photopigment called melanopsin. These cells send signals directly to the suprachiasmatic nucleus — the master biological clock in your hypothalamus — telling it that morning has arrived.
This signal suppresses melatonin, drives the cortisol awakening response, and anchors the circadian clock to the correct phase for the day. In winter, this signal is weakened or absent for many people. The sun rises later. Indoor light levels are a fraction of outdoor light intensity. The circadian clock drifts, melatonin production extends further into the morning, and the result is fatigue, low mood, and the characteristic presentation of seasonal depression.
Light therapy provides the missing morning signal artificially, at sufficient intensity to trigger the same biological response as outdoor morning light.
Does It Actually Work?
Yes, and the evidence is consistent. A 2005 Cochrane review found bright light therapy to be effective for SAD compared to placebo conditions. A landmark 2016 randomised controlled trial published in JAMA Psychiatry found light therapy was as effective as fluoxetine (an SSRI antidepressant) for SAD, and that the combination of both produced significantly better outcomes than either alone.
For non-seasonal depression, the evidence is also emerging and positive — the same 2016 trial was notable because it included non-seasonal major depressive disorder patients, not just SAD, and found light therapy effective in that population too.
For sleep disorders — particularly circadian phase disorders such as delayed sleep phase syndrome and jet lag — the evidence base is strong and well-established. Light therapy is used clinically to advance or delay the circadian clock depending on the direction of misalignment.
For general energy, focus, and mood, studies in healthy populations show consistent improvements in alertness, reaction time, and mood from morning bright light exposure.
How to Use It Correctly
Timing matters more than most people realise. The circadian system is most sensitive to light in the first two hours after waking. Using a light therapy lamp at breakfast has a measurably larger effect on circadian phase than using the same lamp at lunchtime.
Intensity matters. The 10,000 lux recommendation exists because that is the threshold at which the circadian response is reliably triggered. Always check at what distance the rating applies and sit accordingly — a lamp rated at 10,000 lux is not providing that intensity at any distance.
Consistency matters. Light therapy works cumulatively. Two or three days of use will not resolve a circadian misalignment that has built up over weeks. A daily practice through the autumn and winter months is the standard clinical recommendation.
Where the Science Has Moved On
The 10,000 lux standard was established in the early 1980s, largely because that was the intensity at which early clinical trials produced reliable results. It is a robust benchmark, but it is not the final word.
Subsequent research has identified melanopsin as particularly responsive to light around 480 to 490 nanometres — a narrow band in the blue-green range that standard broad-spectrum white light lamps deliver only incidentally, as part of their full spectral output. A lamp that delivers targeted 480nm light alongside its broader output can achieve the same circadian effect at lower overall intensity, or a stronger circadian response at the same intensity.
This does not invalidate the existing generation of SAD lamps — they work — but it points toward a more precise approach that the next generation of light therapy products is beginning to implement.
If you are considering light therapy, the existing evidence is clear enough to act on. A 10,000 lux lamp used consistently in the morning will produce a meaningful benefit for most people who use it correctly. The direction of travel for the technology is toward spectral precision, but the fundamentals have been settled for decades.
