The complete science-based bright light therapy guide

Light reaching specialized retinal cells signals the brain's circadian clock and suppresses melatonin. Timing determines whether the clock shifts earlier, later or receives a stabilizing daytime signal.^{See reference 1,See reference 2}

For seasonal depression, bright light can alter circadian and non-circadian pathways involved in mood and alertness.^{See reference 2,See reference 3}

Illuminance falls rapidly with distance, so a device delivering 10,000 lux at 20 cm may deliver far less across a room.^{See reference 3,See reference 4}

Evidence is strongest for seasonal affective disorder; light can also be used in selected circadian-rhythm disorders.^{See reference 1,See reference 4}

Benefits for non-seasonal depression are promising in some analyses, often as an adjunct, but treatment should be coordinated clinically.^{See reference 2,See reference 5}

A lamp cannot replace assessment for bipolar disorder, suicidality, sleep apnea, medication effects or other causes of fatigue and low mood.^{See reference 3,See reference 6}

Studies use different spectra, intensities, timing and diagnostic groups, so one protocol cannot be generalized to every goal.^{See reference 5,See reference 7}

Consumer product labels may describe maximum lux only at an impractically close distance.^{See reference 6,See reference 8}

Headache, nausea, eye strain, agitation and insomnia can occur; mania or hypomania is the most important psychiatric risk.^{See reference 7,See reference 9}

Choose the smallest version you can repeat under normal conditions. Consistency creates a useful signal; a heroic one-off session does not.^{See reference 1,See reference 2}

Change one variable at a time and write down the protocol. Otherwise an apparent improvement may simply reflect different timing, equipment or conditions.^{See reference 3,See reference 4}

Review the result after a pre-defined period. Continue only when the benefit is meaningful, the burden is acceptable and no safety signal has appeared.^{See reference 5,See reference 6}

This tool is most useful when it solves a defined problem, is feasible to repeat and changes a decision. It is less useful when collected or performed only because a score or influencer made it seem mandatory.^{See reference 2,See reference 4}

People with symptoms, diagnosed disease, pregnancy, recent surgery or complex medicines should adapt the protocol with an appropriate health professional.^{See reference 5,See reference 7}

The foundation remains sleep, physical activity, nutrition, tobacco avoidance and evidence-based medical care. Add this tool only where it improves that foundation.^{See reference 8,See reference 10}