Red Light Therapy Dosage Calculator

Red light therapy (clinically, photobiomodulation or PBM) delivers a dose of light energy to tissue, measured in joules per square centimeter (J/cm²). The dose is determined by two things: how intense the light is at your skin (irradiance, in mW/cm²) and how long you sit there (time). The relationship is simple arithmetic:

dose (J/cm²) = irradiance (mW/cm²) × time (seconds) ÷ 1000.

This is why "how many minutes?" is the wrong question on its own. A strong panel at close range might deliver your target dose in 90 seconds; a weak one at arm's length might take 8 minutes for the same dose. Irradiance also falls off quickly with distance, so the number that matters is the irradiance at your actual treatment distance — not the headline figure on the box, which is often measured at the panel surface.

Wavelength decides depth. Red light (roughly 630–660 nm) is absorbed shallowly, which is ideal for skin and hair. Near-infrared (810–850 nm) penetrates further, which is why deeper targets like joints and muscle use NIR. Jagdeo et al. 2012 (PLoS ONE) measured how much more red and near-infrared light passes through tissue, illustrating why depth and wavelength have to be matched to the goal. Serrage et al. 2019 (Photochem Photobiol Sci) reviews the cellular mechanisms behind these effects, and Holanda et al. 2017 (Lasers Surg Med) covers the basis for near-infrared dosing in deeper tissue.

The biphasic catch — more is not better. Unlike a drug where a bigger dose means a bigger effect up to a ceiling, PBM follows a biphasic dose-response: too little does nothing, an optimal window helps, and too much can blunt or reverse the benefit. Cotler et al. 2015 (MOJ Orthop Rheumatol), reviewing low-level laser therapy for musculoskeletal pain, emphasizes that correct dosing — not maximum dosing — is what separates effective protocols from ineffective ones. That is the whole reason this calculator exists: to put you in the window rather than past it.