The Solar Power Lie Part 2: The Usual Suspects
In a previous blog post we uncovered a massive deception in the red light therapy industry, that we can easily find that many manufacturers are using a cheap solar power meter to report their intensity, yet they tend to read falsely high by over 2x!
We can even find discrepancies from independent reviewers such as Alex Fergus. He used a spectrometer to measure intensity from many of the major brands at 6 inches. Even with his spectrometer, he found that ALL of the brands were significantly less intensity than advertised, especially since most of them claim to deliver >100mW/cm^2.
This time we dig a little deeper, looking at several different models of these solar power meters. Last time we only reviewed the Tenmars Solar Meter TM-206, since this seemed to be the most popular one in the industry. The Tenmars meter has been featured in books, blogs, and used by many major manufacturers. It was meant to represent the issue common to all other brands of solar power meters.
However, not all companies or reviewers are using the Tenmars brand solar power meter, as there are many on the market used for this purpose. So we decided to purchase up many of the common solar power meters to see if we can repeat our results.
Here are the ones we chose:
1. Tenmars Solar Power Meter TM-206
2. TES1333 Solar Power Meter
3. Solarmeter ® Global Solar Power Meter
4. Megger PVM210
5. the daystar meter
6. SANWA Laser Power Meter
The solar power meters numbers 1 through 5 share similar specifications of measuring wavelengths between 400nm-1100nm and a maximum of 1999 W/m^2. We can quickly convert W/m^2 to mW/cm^2 by dividing by 10. So the maximum rated output that these meters measure is 199mW/cm^2.
This time we will measure some high-intensity lights, to help exacerbate the discrepancies. I assembled this 8 Watt (actual power) 660nm LED spotlight recently. This light is probably the most intense Red LED product that I have ever seen.
This is three 3-Watt 660nm LEDs clustered closely together with a narrow beam lens over them. Very intense! Lets see what my meters think about it. The measurements were taken at 4 inches away with the sensor centered on the spot of light.
So we have:
1. Tenmars: 197 mW/cm^2
2. TES1333: 135 mW/cm^2
3. Solarmeter: 122 mW/cm^2
4. Megger: 209 mW/cm^2
5. Daystar: 185 mW/cm^2
6. SANWA: 38.5 mW / 0.636 * 0.925 = 56 mW/cm^2
So we see a wide spread of results here! Imagine how hard it would be to correlate measurements from different manufacturers. We can see it would be impossible to evaluate this light for safety, or for proper dosage for photobiomodulation if we used an unreliable solar power meter. You can check back to our previous blog about flashlights how we got unrealistically high numbers from the solar power meter.
I have noticed that these solar power meters get particularly unreliable if you push them near their limit of 199mW/cm^2 of measurement.
However, I do see a "grouping" of lights such as the 1 Tenmars, 4 Megger, and 5 Daystar that read extremely high at this measurement close to the limit of 200mW/cm^2. The other two meters, the TES1333 and Solarmeter, were a bit more "stable" with their measurements at closer to 120-135mW/cm^2. So I might like to do more testing with those to see if I can make more correlations with my laser power meter.
But I trust that the reality is closest to the SANWA laser power meter at only 56mW/cm^2. We can easily see how the solar power meters read anywhere from 2X to 4X the real results! How can we ever trust them if they read so unrealistically high? What reputable brand would use such sloppy measurement techniques?
To me any brand that is advertising numbers of 200mW/cm^2 based on a solar power meter, is really only outputting around 55mW/cm^2. So this is a good rule of thumb when evaluating lights that claim something ridiculous like >200mW/cm^2.
Now we go back to testing our Oomph light at 6 inches away.
1. Tenmars: 70 mW/cm^2
2. TES1333: 62 mW/cm^2
3. Solarmeter: 67 mW/cm^2
4. Megger: 60 mW/cm^2
5. Daystar: 60 mW/cm^2
6. SANWA: 27 mW / 0.636 * 0.80 = 33 mW/cm^2
Our Oomph light here was designed to specifically mimic the typical intensity seen from red light panels on the market. Again we see here pretty definitively that ALL of the Solar Power meters are easily reading about 2X the real intensity. Unfortunately the Tenmars is leading the pack with the highest intensity number, no wonder it is the most popular meter on the market with manufacturers!
So with so many Solar Power meters on the market, each with varying measurement data, how can we trust the intensity advertising from manufacturers unless it is sent to 3rd parties? The third parties ensures their equipment is properly calibrated, the environments are controlled, they remove the bias from the measurement, and use repeatable industry standard test-methods. Using a solar power meter might be fine for amateurs if they are aware of this offset, but not appropriate for professionals or manufacturers.