Red light therapy devices: what do mW/cm², nm and measuring distance mean?
Key takeaways
- mW/cm² (irradiance, or power density) shows how much light energy reaches one square centimetre of surface per second.
- This number depends on distance and drops quickly: the manufacturer's figure for the Red Light Lamp is 217 mW/cm² at the head, but only 51 mW/cm² at 8 cm.
- Figures from two devices can only be compared if they were measured from the same distance, using a similar method. A number without a distance is not suitable for comparison.
- The wavelength (nm) tells you the type of light: 630–660 nm is visible red, while 810–850 nm is near-infrared, which the eye can barely see or not see at all.
- The coverage area determines how large a body area you light up in one session: a face mask and a 180 cm mat are made for different jobs.
- Before you buy, ask three questions: which wavelengths does it use, what is its power density and from what distance was it measured, and how large an area does it cover?
Contents
- What does mW/cm² show?
- Why does the number depend on distance?
- How to compare two devices
- Wavelength: what do 630, 660 and 850 nm mean?
- What do the spectrum and peak wavelength tell you?
- How large an area does it cover at once?
- Power and time: what is J/cm²?
- How we measured our own devices
- Three questions before you buy
Two red light device listings: one says 200 mW/cm², the other says 50. Which one is stronger? You cannot tell from these two numbers. If the first figure was measured right at the LED and the second from 2.5 centimetres, the second device may even deliver more light at the point where your skin actually is.
In this article we go through what mW/cm² means, why it needs a distance next to it, what wavelength and coverage area tell you, and how all this looks in our own measured data. If you would like to start with the basics (what this technology is, which setting is for what), read our guide to using red light at home first.
What does mW/cm² show?
mW/cm² is the unit of irradiance (light power density): it shows how many milliwatts of light power reach one square centimetre of surface per second. The higher the number, the more light reaches that point. However, the number is always valid for a specific measuring point and distance, so on its own it only tells half the story.
The unit has two parts. The milliwatt (mW) is the power of the light, and the square centimetre (cm²) is the area that power falls on. If a device delivers 50 mW/cm², it means that at the measuring point, every square centimetre receives 50 milliwatts of light.
This is not the same as the device's wattage. The watts on the label are electrical power, in other words what the device draws from the socket. Only part of that becomes light, the rest is heat. The Red Light Mat measurement shows this clearly per LED: the 660 nm LED emits 17.44 mW of light from 41.36 mW of electrical power.
Why does the number depend on distance?
LED light spreads out in a cone, so as you move away, the same light power is distributed over an ever larger area. Each square centimetre therefore receives less and less. The drop is fast: even a few centimetres can mean a several-fold difference. That is why a mW/cm² value only makes sense together with the measuring distance.
The best example: the manufacturer's data for the Red Light Lamp:
| Measuring point | Irradiance |
|---|---|
| At the lamp head (on the surface) | 217 mW/cm² |
| From 8 cm | 51 mW/cm² |
Same lamp, and over 8 centimetres the value falls to less than a quarter. If one listing only shows 217 and another device shows 51, it is easy to draw the wrong conclusion.
Peak or average?
There is a second trap too. Light across an LED surface is not uniform: it is strongest directly above an LED and weaker between two LEDs. The measurement can be taken above a single LED (this is the peak value) or as the average over the whole illuminated surface. The peak value is always higher. In our own data we state which one it is, and in our view this is the minimum a spec sheet should tell you.
How to compare two devices
The mW/cm² figures of two devices can be compared if they were measured from the same distance, in a similar way (peak or average), and ideally at the same brightness level. If any of these is missing, the two numbers are not measuring the same thing. In that case, do not rely on the figure without a distance; ask the seller instead.
The brightness level matters too. Across the five levels of the Red Light Belt, the value measured on the LED surface ranges from 49.7 to 92.4 mW/cm². If a product only lists the figure for its highest level, that is the upper limit, not what you get on every setting.
| What to check | Why it matters | If it is missing |
|---|---|---|
| Measuring distance | Even a few cm can make a several-fold difference | Ask, or do not compare |
| Peak or average | The peak value is always higher | Assume it is a peak value |
| Brightness level | The highest level is the upper limit | Ask which level it was measured at |
| Wavelength channel | Red only, infrared only, or both together | Ask which mode it was measured in |
| Who measured it and with what | Manufacturer's data, in-house measurement or laboratory spectrometer | Treat the number with caution |
Wavelength: what do 630, 660 and 850 nm mean?
Wavelength, given in nanometres (nm), tells you what kind of light a device emits. 630 and 660 nm are visible red light, while 810–850 nm is near-infrared (NIR), which the eye can barely detect or not detect at all. 940 nm lies deeper in the infrared range. A good spec sheet lists the wavelengths as specific numbers, rather than just saying "red and infrared".
Here is how it looks across our range:
- MAX 60 and MAX 180: five wavelengths, 630, 660, 810, 830 and 850 nm.
- MAX 300 and MAX 960: seven wavelengths, 480, 630, 660, 810, 830, 850 and 940 nm.
- Red Light Mat and Red Light Belt: 660 and 850 nm. On the mat they are in a 1:1 ratio, and you can choose to run just one of them or both.
- Red Light Mask: 630 nm red, 590 nm yellow, 460 nm blue, each mode combined with 850 nm near-infrared.
For an overview of which wavelength is used for what, see the wavelength table in our home-use guide. Here it is enough to say: if a device also emits infrared, the listing should state it as a number.
What do the spectrum and peak wavelength tell you?
An LED does not emit at a single wavelength but in a narrow band, which has a strongest point: the peak wavelength. A spectrum measurement shows whether this peak really is where the listing says it is. If a nominal 660 nm LED has a measured peak of 660.7 nm, that indicates precise manufacturing.
The spectrum is measured with a spectrometer. In the laboratory measurement of the Red Light Mat, the two peaks came out at 660.7 and 852.4 nm, a deviation of a few tenths and two nanometres from the nominal 660 and 850 nm. The measured peak of the Red Light Mask's red LEDs is 627.5 nm, against a nominal 630.
Lux is not a good metric for red light. Lux measures how bright light appears to the human eye. The eye cannot detect near-infrared, so even a powerful 850 nm LED can show almost zero lux. If a spec sheet gives a red light device's output in lux, it is not measuring what matters.
How large an area does it cover at once?
The coverage area shows how large a body area the device lights up in a single session. A smaller panel is enough for one body area, while a mat reaches the whole back or front of the body at once. If you want to cover a large area, a bigger device gets the job done in less time, because you do not have to reposition it for each body area.
The size of the devices is a good starting point:
| Device | Size | What it covers at once |
|---|---|---|
| MAX 60 | 316 × 214 mm | One body area, for example the face or a shoulder |
| MAX 180 | 910 × 195 mm | Half the body, for example the back or the length of the thigh |
| MAX 300 | 910 × 298 mm | Half the body, in a wider strip |
| MAX 960 | 1800 × 473 mm | Full body |
| Red Light Mat 900 / 1350 | 180 × 60 cm / 180 × 90 cm | One side of the full body, lying down |
| Red Light Mask | Face-shaped | Face |
The panels have a 30° beam angle. This narrower cone means the light spreads less to the sides and is concentrated on the area in front of the panel. With a stand, the distance also stays the same every time, which, for the reasons above, is at least as important as the panel itself.
Power and time: what is J/cm²?
J/cm² (joules per square centimetre) shows how much light energy reached the surface in total during one session. You calculate it by multiplying the mW/cm² value by the number of seconds and dividing by one thousand. 50 mW/cm² for 10 minutes (600 seconds) therefore gives 30 J/cm².
Two things follow from this. First, a device with lower power density delivers the same amount of energy over a longer time as a stronger one does in a shorter time. Second, distance comes into play here too: if you use the device from further away, less energy reaches the skin in the same amount of time.
Photobiomodulation studies in the scientific literature typically report the applied energy in J/cm². This research is about the technology, not about any specific device. For your own device, the time and distance given in the manual are what you should follow.
How we measured our own devices
For the measured data of MovTech devices, we always state what was used to measure, where and from what distance. The Red Light Mat was measured with a laboratory spectrometer directly on the surface, the Red Light Mask figure is a manufacturer's measurement from 25 mm, and the Red Light Belt values are given per level, on the LED surface. This way you can see what each number refers to.
| Device | Measured value | Measurement conditions |
|---|---|---|
| Red Light Mat | approx. 160–180 mW/cm² (660 + 850 nm combined) | HAAS1200 laboratory spectrometer, 0 cm, peak value measured above a single LED |
| Red Light Mask | 53.5 mW/cm² (red + infrared mode) | Manufacturer's measurement, from 25 mm |
| Red Light Belt | 49.7–92.4 mW/cm² (levels P1–P5) | Spectrometer, on the LED surface |
| Red Light Lamp | 217 mW/cm², 51 mW/cm² from 8 cm | According to the manufacturer's data |
The table also shows why we do not put these numbers into a single ranking. The mask's 53.5 mW/cm² measured from 25 mm and the mat's peak value measured from 0 cm above a single LED describe different situations, so side by side the two numbers tell you nothing. They do, however, tell you a lot about what each device can do.
Detailed measurement data can be found in the "Specifications" section of each product page and in the FAQ, together with the measured spectrum curves for the Red Light Mat.
Three questions before you buy
Before choosing a red light device, look for answers to three questions: which wavelengths does it use, what is its power density and from what distance was it measured, and how large an area does it cover at once? If any of them goes unanswered, ask the seller before you decide.
- Which wavelengths does it use? Look for specific numbers in nanometres. If it includes infrared, that should be given as a number too.
- What is the power density, and from what distance was it measured? The mW/cm² needs a distance next to it, and ideally you should also find out whether it is a peak or an average value, and at which level.
- How large an area does it cover at once? Think about which body area you would use it on. A mask for the face, a belt for the lower back, a panel or mat for large areas.
Not sure? Write to us and we will tell you what measurement data each of our devices has, and what it refers to. If you would like to try one first, the MAX panels and the Full Body Mat are also available to rent.
Safety: do not look directly into a high-brightness panel; use the eye protection supplied with the device. If you are pregnant, take medication that causes light sensitivity, or have any existing health condition, ask your doctor first. Red light devices are wellness devices, not medical devices, and are not intended to treat any health condition.
In summary
mW/cm² is a useful number, but only together with the distance. At 8 centimetres the Red Light Lamp delivers less than a quarter of what it does at its surface, which is why a figure without a distance is not suitable for comparison. Add the wavelengths as specific numbers and the coverage area, and these three together will tell you which device suits what you want to use it for.
On the product pages of our red light devices, the measurement conditions are always shown alongside the measured data. If you have a question about any number, get in touch.
