Red Light Therapy Glossary: Wavelength, Irradiance, Dose and More
Quick answer: Spec sheets use a handful of terms: wavelength (color), irradiance (power per area), dose (energy per area), duty cycle and beam angle. Know these five and you can compare any two devices fairly.
Red light listings are full of technical words. This glossary defines the common ones in plain language.
Glossary
| Term | Plain meaning |
|---|---|
| Wavelength | The color of light, measured in nanometers (nm) |
| Near infrared | Invisible light just beyond red, often about 850nm |
| Irradiance | Power reaching a surface, in mW/cm2 |
| Dose | Energy delivered, in J/cm2 |
| Photobiomodulation | The scientific term for low level light exposure studies |
| Beam angle | How widely the light spreads from the LEDs |
| Duty cycle | Whether the light is continuous or pulsed |
The one formula to know
J/cm2 = mW/cm2 x seconds / 1000. Example numbers for arithmetic only: 100 mW/cm2 for 120 seconds is 100 x 120 / 1000 = 12 J/cm2. Our dose guide and irradiance explainer go further.
Putting terms to use
The FX300 spec data is in the irradiance specs post. For how red and near infrared compare, read 660nm vs 850nm.
Common mistakes
- Comparing irradiance values taken at different distances.
- Confusing power in watts with irradiance.
- Trusting a number with no stated distance.
Frequently asked questions
Why does distance matter?
Irradiance falls as you move away from the device.
Is a bigger number better?
Not automatically. Check the distance and the manual.
Are these devices FSA or HSA eligible?
Eligibility depends on your plan. Read our FSA and HSA guide.
Browse the red light therapy collection. This guide is educational and is not intended to diagnose or replace clinician advice.
How we create this guide: We write from product specs and review each claim against our editorial standards.
Updated October 2026.
