What Is Irradiance in Red Light Therapy and Why Does It Matter?
Published May 15, 2026. Updated October 2026.
Quick answer
Irradiance is light power per area, written in mW/cm², and it only means something when a distance is attached. It is different from LED count and from total watts. Multiply it by time in seconds and divide by 1000 to get energy in J/cm². This guide is arithmetic and spec reading, not a claim about outcomes.
Tools
Use the irradiance by distance chart to look up a figure, the red light dose calculator to turn it into energy, the session time table, or compare AWA devices.
What irradiance means
Irradiance is the amount of light power that arrives on a surface, divided by the area of that surface. For red light devices it is written in milliwatts per square centimeter, mW/cm². A higher figure means more power is landing on each square centimeter at the stated distance. It says nothing on its own about any outcome, and it is not the same thing as how many LEDs a device has or how many watts it draws from the wall.
Irradiance is the input to the dose arithmetic in our dose calculation guide: multiply it by time in seconds and divide by 1000 to get energy in J/cm².
Irradiance versus other numbers on a product page
- LED count. A count of how many emitters are on the face of a device. More LEDs can mean more total light, but not necessarily more on each square centimeter.
- Wattage. Often the power drawn by the whole device. It includes the driver, the fans and heat that is not light.
- Irradiance. Light power per area at a distance. This is the number that connects directly to the energy arithmetic.
- Energy (J/cm²). Irradiance multiplied by time. Only meaningful when the time is stated.
Why the distance is part of the spec
Move a panel closer and the light is concentrated on a smaller patch. Move it back and the same light is spread wider. A simple physics rule, the inverse square law, says that for a single small point source, doubling the distance cuts irradiance to a quarter. Real panels are flat arrays of many LEDs, so they do not follow that rule exactly, especially at short range.
You can see this in the published AWA figures. From 6 inches to 12 inches, the stated FX300 figure goes from 83.5 to 43.3 mW/cm², a ratio of 0.52. The stated FX500 figure goes from 94 to 73.8 mW/cm², a ratio of 0.79. A pure inverse square rule would predict 0.25 for both. The lesson is not a formula to memorize. It is that each device has its own curve, and the only reliable number is one stated at your distance.
| Distance | FX300 stated irradiance (mW/cm²) | FX500 stated irradiance (mW/cm²) |
|---|---|---|
| 1 inch | 220 | not listed |
| 2 inches | 145 | 220 |
| 3 inches | 116 | 197 |
| 6 inches | 83.5 | 94 |
| 12 inches | 43.3 | 73.8 |
Figures are the ones published in the AWA irradiance specs guide. Check the product page for the current specification.
Worked examples (arithmetic only)
Each example below uses a stated figure from the table above and the energy formula. They are arithmetic examples and not a recommended session.
Arithmetic example 1: FX500 stated at 94 mW/cm² at 6 inches. For 10 minutes (600 seconds): 94 x 600 / 1000 = 56.4 J/cm².
Arithmetic example 2: the same panel stated at 73.8 mW/cm² at 12 inches, also 10 minutes: 73.8 x 600 / 1000 = 44.28 J/cm², about 44.3. Doubling the distance changed the energy figure by far less than half on this panel, which is what the ratio above predicts.
Arithmetic example 3: the FX300 stated at 83.5 mW/cm² at 6 inches for 10 minutes: 83.5 x 600 / 1000 = 50.1 J/cm². At 12 inches, 43.3 x 600 / 1000 = 25.98 J/cm².
Arithmetic example 4, a face mask: the irradiance specs guide lists the AWA LX500 face mask at 30 to 40 mW/cm² at skin contact. Taking 35 as a midpoint purely for the arithmetic, 10 minutes gives 35 x 600 / 1000 = 21 J/cm². The midpoint is an invented simplification, and a mask has no distance to adjust.
Unit conversions you may meet
- 1 W/cm² = 1000 mW/cm².
- 1 mW/cm² = 10 W/m².
- 10 mW/cm² = 100 W/m².
- 1 J = 1 W for 1 second, so 1 mJ/cm² = 1 mW/cm² for 1 second.
If a spec sheet uses W/m², divide by 10 to get mW/cm² before using any formula here.
How to read a spec sheet
Use this table as a checklist when you compare any two devices. A spec that cannot answer these questions is hard to compare.
| What to check | Why it matters | What a clear spec sheet shows |
|---|---|---|
| Unit | mW/cm² and W/m² differ by a factor of 10, and W and mW by 1000 | The unit written out, not just a bare number |
| Distance | Irradiance changes with distance, so a number without one cannot be compared | A distance such as 6 inches next to every figure |
| Where it was measured | Centre, average and edge of a panel can differ | A note saying where on the surface the figure applies |
| Contact or gap | A mask sits on the skin, a panel sits at a gap | Contact stated for wearables, gap stated for panels |
| Wavelength | Some sheets give one total figure for several wavelengths | Whether the figure is per wavelength or combined |
| Total power | Total watts do not say what lands on each cm² | Irradiance listed separately from device wattage |
For a device you already own, the manual and product page are the right source for working distance and session time. Our own panels list working distances on their pages: see the AWA FX300 panel and the AWA FX500 panel.
Common mistakes
- Comparing a figure stated at 2 inches with one stated at 12 inches.
- Using LED count or total watts as if they were irradiance.
- Assuming irradiance stays the same across the whole face of a panel.
- Forgetting that a mask is measured at contact, so there is no distance to adjust.
- Mixing mW/cm² and W/m² without converting.
- Reading a high irradiance number as a statement about outcomes. It describes the light a device emits, not what happens to anyone using it.
Before you use any light device: read the label, follow the device manual, and use eye protection as directed. Ask a doctor first if you have a medical condition, take medications, are pregnant, or have light sensitivity.
Related guides in this series
- How to calculate a red light therapy dose
- AWA FX300 and FX500 irradiance specs
- 660nm vs 850nm wavelength guide
- How long a session runs, by the manual
- Using a device beyond its manual
Device pages
Read the full page and label for each device before you use it: AWA FX300 panel, AWA FX500 panel, AWA LX500 face mask. You can also browse all AWA red light therapy devices.
Frequently asked questions
What is irradiance in simple terms?
Irradiance is the light power arriving on a surface divided by the area of that surface, usually written in mW/cm². It is a property of the light at a given distance.
Why does a spec need a distance?
Irradiance changes as you move a device closer or further away. A figure with no distance attached cannot be compared with another figure.
Is irradiance the same as LED count or wattage?
No. LED count and wattage describe the device as a whole. Irradiance describes how much light power lands on each square centimeter at a stated distance.
How do I turn irradiance into energy?
Multiply irradiance in mW/cm² by time in seconds, then divide by 1000 to get J/cm². This is arithmetic about the light emitted.
Do masks and panels use the same measurement point?
Not usually. A mask sits against the skin, so its figure is stated at contact. A panel is stated at one or more distances, such as 6 inches or 12 inches.
Sources
- FDA: General Wellness policy guidance (CDRH). Final guidance dated January 2026 that sets out the agency's compliance policy for general wellness products. It is a policy document, not a statement about any one device.
- FDA: Laser Products and Instruments. Describes FDA laser hazard classes I to IV, notes that higher classes carry warning labels, and states that LEDs are not subject to the federal laser product performance standard.
- FDA: Premarket Notification 510(k). Explains that a 510(k) is a premarket submission showing a device is substantially equivalent to a legally marketed device, and that a company must receive an FDA order clearing the device before marketing it in the U.S.
Regulatory note: select devices carry FDA 510(k) clearance for specific, limited uses. Most light devices are sold as general wellness products. Read each product page and label.
How we create this guide
AWA sells red light therapy devices. We write these guides to explain how devices work and how to choose and use one. This is general information, not medical advice. Read each product page and label. See our editorial standards.
