How Long Should A
Light Session Be?
In photobiomodulation, what matters is dose — the amount of light energy delivered to your skin, measured in joules per square centimetre (J/cm²). Dose is simply how bright the light is at your body (irradiance) multiplied by how long you sit in it. Set a target and your device's measured output below, and this tool estimates your session time live.
Presets set a typical starting target — fine-tune it freely. Ranges are illustrative general guidance, not a prescription.
Use your device's measured irradiance at your treatment distance. REDelios ONE figures will be published with the spec sheet — enter your own measured value here in the meantime.
Irradiance falls off sharply as you move away from the panel — roughly with the inverse square of distance. Double the distance and the light reaching you can drop to around a quarter. A figure measured at 15 cm tells you little about 45 cm, so always measure — and dose — at the distance you actually use.
≈ 250 seconds of continuous exposure to reach 10.0 J/cm².
250 s = 10.0 × 1000 ÷ 40
Energy, Not Effort.
And More Isn't Always Better.
Three ideas explain almost everything about light dosing — the equation, the biphasic curve, and the role of distance.
The Equation
Dose (J/cm²) = irradiance (mW/cm²) × time (s) ÷ 1000. Brighter light reaches the same dose faster; dimmer light simply needs more time. The number that matters for biology is the dose — the total energy delivered — not the clock.
The Biphasic Curve
Photobiomodulation follows a biphasic dose-response: too little light does little, an optimal window helps most, and piling on far more can flatten or even reverse the benefit. More is not always better — there's a sweet spot, which is why dosing is worth estimating at all.
Distance Changes Everything
Irradiance drops steeply with distance — roughly inverse-square. The same panel delivers a very different dose at 15 cm versus 45 cm, so the only honest input is one measured at the distance you actually treat from.
Wellness tool, not medical advice. This calculator is an educational estimator for general light-and-wellness use. Dose ranges are illustrative and do not constitute a treatment protocol, diagnosis, or medical recommendation. Always follow your device manufacturer's safety and distance instructions, protect your eyes, and consult a qualified health professional before using light for any medical condition.