Red Light Dose Calculator
Energy dose in joules per square centimeter (J/cm²) is irradiance multiplied by time. Enter the irradiance in mW/cm² and your session minutes, or work backwards from an energy number to a time. Everything runs in your browser. Nothing is saved or sent.
Information only. Not medical advice.
Red light dose calculator
Worked examples
Example numbers for arithmetic only. These show how the formula works. They are not session recommendations.
Energy from time. The FX300 is published at 83.5 mW/cm² at 6 inches. Use it for 5 minutes, which is 300 seconds.
83.5 × 300 ÷ 1000 = 25.05 J/cm²
Time from energy. The FX500 is published at 70 mW/cm² at 15 inches. Pick an invented energy number of 30 J/cm².
30 × 1000 ÷ 70 = 428.6 seconds, about 7.1 minutes
How the formula works
Irradiance is power arriving per unit of area. Energy is power accumulated over time. Milliwatts per square centimeter times seconds gives millijoules per square centimeter, and 1000 millijoules make one joule.
- Start with the irradiance in mW/cm² at the distance you will use.
- Turn minutes into seconds by multiplying by 60.
- Multiply irradiance by seconds.
- Divide by 1000 to get J/cm².
To work backwards, use seconds = J/cm² × 1000 ÷ mW/cm², then divide by 60 for minutes.
What this calculator cannot tell you
- It does not know your device. Irradiance depends on the device and the distance, so read any figure together with its distance.
- Published figures are stated at specific points. Readings at the edge of a panel can differ.
- The result describes light emitted at a surface. It says nothing about what a session will do for a person.
- It does not recommend a dose, a distance or a session length. Your manual does that.
Frequently asked questions
What is the formula for red light dose in J/cm²?
Energy in J/cm² equals irradiance in mW/cm² multiplied by time in seconds, divided by 1000. For example, 50 mW/cm² for 100 seconds is 50 × 100 ÷ 1000 = 5 J/cm². These are example numbers for arithmetic only.
Why divide by 1000?
Irradiance in milliwatts per square centimeter multiplied by seconds gives millijoules per square centimeter. There are 1000 millijoules in a joule, so dividing by 1000 converts the answer to J/cm².
Where do the preset irradiance values come from?
They are the irradiance figures AWA publishes for the FX300 and FX500 at stated distances. Values between the listed distances are not measured, so the presets only offer the published points. You can type any other value yourself.
Does this calculator tell me how long to use my device?
No. It only does arithmetic on the numbers you enter. It does not recommend a dose, a distance or a session length. Follow the manual and label that came with your device, and ask a doctor first if you have a medical condition.
Related guides and tools
- Dose guide: irradiance, time and energy explained
- Irradiance guide: what the number on a spec sheet means
- Distance guide: time, distance and dose arithmetic
- AWA FX300 and FX500 irradiance specs
- Irradiance by distance chart
- Session time table
- AWA FX300 panel and AWA FX500 panel, or browse all AWA panels
How we create this guide
AWA sells red light therapy devices. We build these tools and guides to explain how devices work and how to choose and use one. The numbers come from AWA product pages and our published irradiance specs. This is general information, not medical advice. Read each product page and label. See our editorial standards.
Updated October 2026.
Information only. Not medical advice.