Light Therapy Wavelengths and Doses Explained
How to read a PBM or light-box spec: nanometers, irradiance (mW/cm²), energy (J/cm²), distance, and time. LED vs laser, biphasic dosing, and why a pretty bed can still be underdosed.
Overview
Wavelengths and doses are how you keep a clinic honest. Photobiomodulation is not “more LEDs = more mitochondria.” You need wavelength (nm), irradiance at the skin (mW/cm²), time, and thus fluence (J/cm²). Bright-light boxes use a different unit: lux at the eye. Mixing those systems is how people buy a sauna for SAD.
The PBM map
Red: ~630–670 nm, more superficial (skin, shallow tissue).
Near-infrared: ~800–850+ nm, deeper. Still PBM if irradiance is modest.
LED vs laser (LLLT): both can deliver photons. Lasers are tighter beams; panels cover area. Coherence is less important than dose at the target.
Why spa numbers lie
Irradiance falls with distance (roughly inverse-square for small sources). A bed rated at the diode is not the dose at your sternum. PBM has a biphasic (Arndt–Schulz-like) pattern in the literature: too little does nothing; too much can blunt the effect. “20 minutes on full power, pressed to the face” is not automatically better. Ask for mW/cm² at the treatment distance, not a marketing wattage for the whole fixture.
Benefits
Lets you compare a panel to a paper instead of a brand
Separates lux (SAD) from J/cm² (PBM)
Explains why distance and time are the real prescription
LED vs laser without mysticism
Flags heaters posing as NIR PBM
The Procedure
1
Get the spec sheet
2
Measure the job
3
Fix distance
4
Protect eyes
Preparation
Ask the clinic to write down wavelength, irradiance, time, and distance before you pay for a package.
Recovery & Aftercare
If you are hot, sunburned, or seeing spots, the dose was wrong.
Risks & Considerations
Underdosing (wasted membership), overdosing (irritation, possible inhibitory PBM), eye injury, and thermal burns from mislabeled infrared heaters.
Frequently Asked Questions
References
[1]
Chung H. et al. The nuts and bolts of low-level laser (light) therapy (Ann Biomed Eng, 2012).
https://doi.org/10.1007/s10439-011-0454-7[2]
Huang Y.Y. et al. Biphasic dose response in low level light therapy (Dose Response, 2011).
https://doi.org/10.1089/pho.2012.3388[3]
Hamblin M.R. Photobiomodulation mechanisms (AIMS Biophys, 2017).
https://doi.org/10.3934/biophy.2017.3.337[4]
Golden R.N. et al. Light therapy for mood disorders (Am J Psychiatry, 2005).
https://doi.org/10.1176/appi.ajp.162.4.656
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