The Solar Power Lie - The Dark Deception of Red Light Therapy Industry
Have you been duped into buying a high intensity LED panel that claims a suspiciously round number like 100mW/cm^2 at 6 inches? We often see extremely high intensity numbers being advertised, but these numbers are based on improper measurement tools, techniques, and biased rounding. This blog will help to elucidate the greatest bait-n-switch being performed in the red light therapy industry today.
One of the most important parameters of red light therapy is indeed the intensity! This is normally described as the power per square area, in units of milliWatts per Square Centimeter (mW/cm^2). This is a physical quantity that is easy to measure, however there has been some issues with this industry selecting the wrong tool for the job.
Very often we see the go-to measurement device is a cheap Solar Power Meter. As the name implies, this helps estimate the power of sunlight or full spectrum light typically used in the plant growing industry or solar energy industry.
At the surface level, an inexperienced person might select one of these tools based on the following logical fallacies:
1. They claim to measure a range from 400nm to 1100nm
2. The measured output is in W/m^2, which is easily converted to mW/cm^2
So it might seem like these devices are appropriate for measuring LED red light therapy in the range of 600nm to 1000nm and displaying the power per square area measurement that we need.
However, these devices are clearly designed to measure a broad spectrum light (white light, sunlight, or grow lights). Thus the calibration is made for the broad range to estimate the equivalent "solar" output of a light. All of these solar power meters use a Silicon Photodiode to take the measurement that must be calibrated to adjust for their sensitivity. When we look simply at the sensitivity curve for the silicon photodiode, we see a very important trend to take note of.
Above is the typical spectral response with a silicon photodiode. This type of diode is universal to nearly all Solar Power meters and many laser power meters, so they all have a similar spectral response like this curve.
The key here is the dramatic rise in sensitivity as wavelength moves towards a peak of 980nm in infrared. So for reference, a measurement of 850nm light will have a response twice as strong as 500nm. So for example if a solar power meter is calibrated to the 500nm wavelength but we measure a 50mW/cm^2 850nm LED, then it will display a falsely-high 100mW/cm^2 on the power meter.
Measurements of power have been happening for a very long time for the laser industry. Often the Power Meters for lasers will also this same type of Silicon Photodiode. However, these power meters are properly calibrated to a particular wavelength, and often have software to make correction factors based on different wavelengths. We recently purchased a SANWA laser power meter and this sensitivity curve is displayed on the inside of the meter to help the user choose the correct correction factor based on the wavelength they measure.
Picture above of the inside of the SANWA Laser Power meter, showing the sensitivity curve and table of correction factors based on wavelength.
This measurement variation based on the calibration curve is likely the root cause of false-advertising of intensity in the Red Light Therapy industry (in addition to biases when companies measure their own equipment). At GembaRed we have played around with a cheap Tenmars TM-206 Solar Power meter, but it was clear to us it was outputting unrealistic measurements.
This is why we have always sent our GembaRed lights away to a professional 3rd party testing lab. This ensures that the laboratory:
1. Uses the correct measurement equipment.
2. Keeps the equipment properly calibrated.
3. Measures in a controlled environment.
4. Follows industry standard testing protocols.
5. Removes our bias if we were to measure it ourselves.
Lets take a look at some comparison measurements between our GembaRed Lights and the 3rd party lab measurements.
So we see here a large discrepancy between the Tenmars Solar Power meter and the 3rd party results. The Beam light is the closest to the 3rd party because it uses only 660nm LEDs, which is lower on the sensitivity curve. But it is still 31% higher on the Tenmars meter!
However the Rex and Oomph panels use many 830nm or 850nm LEDs, we see a bigger discrepancy of almost 2x the intensity! That is because the near-infrared 850nm is much higher on the sensitivity curve so will give us higher measurements.
A sloppy brand might happily advertise the Solar Power Meter measurements because they are much higher than a properly calibrated measurement. You can even use the Tenmars meter on photographs or videos to give social "validation" to your advertised intensity. However it is clear that it is not the right tool for the job.
Above is our measurement of the GembaRed Oomph Uno with the Tenmars Solar Power meter at 6'' away. The display show 704 W/m^2, which is 70.4 mW/cm^2. While we would love to advertise this as our "high" intensity, it is not accurate by almost 2x.
Above we see a photo I requested my laboratory to take of their measurement setup. They are using a Spectroradiometer, which is why they can simultaneously verify the wavelengths and integrate the intensity at each individual wavelength. This helps avoid the issue with the silicon photodiode power meters being wavelength-dependent sensitivity.
Recently we have been testing with this SANWA laser power meter. This is one of the most affordable laser power meters we have found and purchased through Sper Scientific. However, there is some math we need to perform to get an accurate number. The number on the screen is 27mW for the Oomph measurement at 6 inches. To get the mW/cm^2, we need to divide by the surface area of the sensor. The diameter of the sensor is 9mm, so we get the area by pi*(.45)^2 = 0.636 cm^2. Then we need to multiply by a correction factor for the wavelength, since we are blending together red and infrared, we choose a correction factor in the middle, 0.80. So the measured intensity is 27/0.636*0.80 = 34 mW/cm^2. So with a mindful correction factor applied, this power meter is much more accurate than the standard Solar Power Meters that are being used!
Still not convinced? There is even a Peer-Reviewed article that precautions against using silicon photodiode power meters for the measurement of LLLT or PBM parameters. This is one of the many reasons why the parameters and results of red light therapy are so widely variable, because many scientists in the industry aren't accurately verifying the intensity. They reiterate the concerns that we make about the sensitivity curve of the silicon photodiode:
"Although this type of measurement system is most popular within LLLT literature (Table 1), measurements from these devices should be interpreted cautiously. The spectral sensitivity differs with wavelength due to the quantum efficiency of the photodiode and generally has a better response at longer wavelengths. Thus, if broadband light sources are measured, the power emitted at short and longer wavelengths maybe be under- or over-estimated, respectively."
So here we see that scientists are fully aware that photodiode power meters must be interpreted cautiously otherwise you will allow too much measurement error. They highlight that lower wavelengths have a lesser response, and higher wavelengths will have a stronger response, as we show in the sensitivity diagram. The article is aptly named "The Dark Art of Light Measurement: Accurate Radiometry for Low-Level Light Therapy."
Normally when purchasing a product, the consumer must trust the company that their advertised numbers are correct. If I purchase a bottle of magnesium supplements that advertise 1000mg per serving, but they use an uncalibrated scale to measure that serving, and I actually only get 400mg per serving, this would be a big problem!
If you buy a red light panel that advertises 100mW/cm^2 based on uncalibrated equipment, but you are getting less than 50mW/cm^2 at the advertised distance, then this is a terrible problem! This not only hurts the consumer base, but it also affects the entire science and progress of the red light therapy industry!
At GembaRed our commitment is not only been to competitive price, but also accurate and transparent advertising. Our "low intensity" products are being hurt by an industry that is inaccurately measuring their products and promoting high intensities that are unnecessary and unsafe to begin with.
If you think you have a light panel with suspiciously high reported intensity, or are obviously using a Solar Power meter... Then send them this article and demand accurate 3rd party measurements!
Per the FTC guidelines if there are false or misleading claims that are affecting consumers' purchasing decisions, then the consumer is entitled to financial compensation. Often times intensity is one of the primary deciding factors when purchasing one of these panels, so this is a major concern for manufacturers who are participating in using these solar power meters to report inaccurate numbers.
Or worse, many of these companies HAVE 3rd party measurements, but are omitting the true results. This is another form of deception might be frowned upon by the FTC.
The dark art of light measurement: accurate radiometry for low-level light therapy.