What it is
Light is the primary signal that sets the body's internal clock. When and how much light you get — morning, daytime and evening — shapes sleep timing, alertness and metabolic rhythm.
What is currently understood
The effect of morning light on circadian timing and of evening light on delaying sleep is well established in human studies. Timing and consistency matter more than any device.
What is not established
Precise protocols sold as optimisation — exact lux counts, exact minutes — outrun the evidence. Individual sensitivity varies widely.
Regulatory status
Not applicable — this is a lifestyle and behaviour topic, not a regulated product.
How it comes up in coaching
It is one of the highest-leverage, zero-cost levers in the whole practice. Coaching builds light timing into the daily structure alongside sleep. Nothing here is a recommendation.
This page is educational. It is not medical advice, not a recommendation, and not an offer to supply anything. Whether any intervention is appropriate for you is a decision for a licensed provider.