Joules Per Session: How to Read Your Red Light Therapy Dose

Published October 2026. Updated October 2026.

Joules versus joules per square centimeter

People say "joules per session" and mean two different things. Sometimes they mean the total energy a device sends out during a session, measured in joules. Sometimes they mean the energy density at the surface, measured in joules per square centimeter. A spec sheet, a calculator and most research papers use the second one, because a small and a large surface lit by the same device get very different amounts per square centimeter.

Think of rain. The total water that fell on a town is one number. The depth of water in a bucket is another. J/cm² is the bucket depth. Total joules is the whole town.

Step by step: from spec sheet to a session number

1. Find the irradiance in mW/cm² and the distance it was stated at. For AWA panels these are in the irradiance specs guide.
2. Convert the session length to seconds. Ten minutes is 600 seconds.
3. Multiply irradiance by seconds, then divide by 1000. The answer is J/cm².
4. Optional: multiply by the area in cm² if you want total joules.

The first three steps are the same arithmetic as in the main dose guide. This article focuses on what the final number does and does not describe.

Worked table: FX300 per session

Each cell below is J/cm² = stated irradiance x time. The irradiance values are the published FX300 figures from the specs guide. The times are chosen to show the arithmetic and are not a session recommendation.

Notice how distance changes the whole row. At 1 inch the same 5 minutes gives about 66 J/cm². At 12 inches it gives about 13. The device did not change. The geometry did.

Worked table: FX500 per session

More FX500 distances are on the irradiance by distance chart. Your manual, not this table, gives the distance and session length for your device.

From J/cm² to total joules

Total joules only make sense if you know how much surface the light covers. Here is an arithmetic example using the FX300 at 6 inches for 5 minutes, which is 25.05 J/cm². The areas below are example numbers for arithmetic only.

The same 25.05 J/cm² corresponds to very different totals depending on area. That is why total joules is a poor number for comparing devices. A device that lights a large area will always show a larger total than one that lights a small area at the same irradiance.

What a dose number cannot tell you

• It cannot tell you what is suitable for you. Only the device manual sets session length and distance for that device, and a qualified professional can answer medical questions.
• It cannot tell you how the light lands on a curved surface, through clothing or at an angle.
• It cannot compare two devices unless both are stated at the same distance and measured the same way.
• It does not say that a bigger number is better. We make no such claim.

A short checklist before you trust a joules figure

• Is the unit J or J/cm²? If it says only "joules", ask what area it applies to.
• Is the distance stated?
• Is the time stated in seconds or minutes?
• Is the irradiance a peak or an average?
• Did the figure come from the manufacturer, or from your own measurement?

Common mistakes

• Confusing joules with J/cm², which is a different unit.
• Forgetting to convert minutes to seconds before multiplying.
• Skipping the divide by 1000 step, which makes the answer a thousand times too big.
• Using a figure stated at one distance while sitting at another.
• Comparing devices by total joules without comparing the area they light.
• Reading a calculated number as advice about how long to run a session.

Before you use any light device: read the label, follow the device manual, and use eye protection as directed. This guide is general information about arithmetic and planning, not medical advice. For medical questions, speak to a qualified professional.

Related guides and tools

• How to calculate your dose: the main guide
• What irradiance means on a spec sheet
• AWA FX300 and FX500 irradiance specs
• How long a session runs, by the manual
• Time, distance and dose arithmetic
• Red light dose calculator
• Session time table

Device pages

Read the full page and label for each device before you use it: AWA FX300 panel, AWA FX500 panel. You can also browse the AWA panels, or the Learning Center for more guides.

Frequently asked questions

What does joules per session mean?

It can mean total energy in joules or energy density in J/cm². Most spec sheets and studies use J/cm², which is irradiance in mW/cm² times seconds, divided by 1000.

How do I turn J/cm² into total joules?

Multiply by the area in square centimeters that the light covers. The area is often an estimate, so read the answer as a rough figure.

Is a higher joule number better?

This guide makes no claim that it is. A dose number describes emitted light and nothing more. Follow your manual for session length and distance.

Why are my numbers different from a calculator?

Check units first. The most common causes are mixing minutes with seconds, skipping the divide by 1000 step, or using an irradiance stated at a different distance.

Where do the AWA irradiance figures come from?

They are the published FX300 and FX500 irradiance values at stated distances, listed in the AWA irradiance specs guide.

Sources

• FDA: General Wellness: Policy for Low Risk Devices. January 2026 guidance from the FDA Center for Devices and Radiological Health on its compliance policy for low risk general wellness products. It is a policy document, not a statement about any one device.
• FDA: Premarket Notification 510(k). Explains that companies generally must submit a 510(k) before marketing certain medical devices in the U.S., showing substantial equivalence to a legally marketed device.

Regulatory note: select devices carry FDA 510(k) clearance for specific, limited uses; most are sold as general wellness products. Read each product page and label.