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Reviewed August 31, 2026

Why Two Meters Give Two Answers: Solar Meters vs Spectrometers

Some brands publish two irradiance figures for the same panel, measured at the same distance, on the same day. One is roughly twice the other.

Neither is a lie. They are measuring different things, and only one of them describes the light that matters to you.

The published pairs

These are the manufacturers' own numbers, taken from their own product pages. Every figure is at six inches unless noted.

  • Mito Red MitoPRO 300X: greater than 130 mW/cm2 by solar meter, greater than 56 by spectroradiometer. Ratio 2.3.
  • Mito Red MitoPRO 750X: greater than 160 solar, greater than 70 spectroradiometer. Ratio 2.3.
  • Mito Red MitoPRO 1500X: greater than 160 solar, greater than 73 spectroradiometer. Ratio 2.2.
  • Mito Red MitoPRO Mobile, at three inches: 100 solar, 40 spectroradiometer. Ratio 2.5.
  • Block Blue Light PowerPanel MID: 158 solar, 61 spectrometer. Ratio 2.6.
  • Block Blue Light PowerPanel PRO: 160 solar, 68 spectrometer. Ratio 2.4.
  • Block Blue Light PowerPanel MEGA: 167 solar, 89 spectrometer. Ratio 1.9.
  • Rouge Pro G4: 164 solar, 90 spectrometer. Ratio 1.8.

The pattern holds across three unrelated brands and eight devices. The solar figure runs somewhere between 1.8 and 2.6 times the spectrometer figure.

That consistency is the point. This is not one brand exaggerating. It is a systematic property of the instrument.

What a solar meter is actually for

A handheld solar power meter, sometimes sold as a pyranometer, is a tool for solar panel installers. You point it at the sky and it tells you how many watts per square metre are arriving.

To do that job it uses a broadband detector that responds across a wide range of the spectrum and sums everything it receives into one number. It is calibrated against daylight, meaning its reading is corrected on the assumption that the incoming light has the broad spectral distribution of sunlight.

Both of those design choices are correct for measuring sunlight. Both break when you point the meter at an LED panel.

Why that produces a bigger number

Three things happen at once.

It integrates the whole spectrum rather than your therapeutic bands. A red light panel does not emit only at its stated peaks. Every LED has a bandwidth around its peak, drivers and housings produce stray output, and multi-wavelength panels emit across several bands at once. A solar meter cannot separate any of that. It adds it all up.

This matters most on panels with long wavelength lists. The Rouge G4 line runs eight wavelengths, from 630nm through to 1060nm. A single solar reading sums all eight, including bands with far thinner supporting evidence than 660 and 850. Wavelengths covers which ones the research actually used.

The calibration assumption is wrong. The meter's response is corrected for a broad daylight spectrum. Narrowband LED output at 660nm and 850nm looks nothing like daylight, so the correction that makes the meter accurate outdoors becomes a source of error indoors.

It counts the room. Ambient light, reflections off nearby walls and mirrors, and infrared from the panel housing all reach the detector. In a normally lit room, part of your reading was never coming from a therapeutic LED at all.

Mito Red states the mechanism on its own product pages: consumer meters read the full spectrum and report higher numbers, while professional spectroradiometers isolate the specific therapeutic wavelengths actually emitted.

What a spectrometer does differently

A spectroradiometer disperses incoming light and reports irradiance per nanometre across the spectrum, rather than one summed figure.

That lets you do the thing that matters. You can integrate only the band you care about and ask how many milliwatts per square centimetre are arriving at 660nm, separately from 850nm, with everything else excluded.

It is a laboratory instrument costing orders of magnitude more than a solar meter, which is precisely why most of the market does not own one.

Which number to use for dosing

Block Blue Light answers this on its own product pages, and the phrasing is unusually direct for a marketing document. The spectrometer figure is there to ensure accuracy for dosing purposes. The solar meter figure, in their words, is for competitor comparison purposes only and should not be used for dosing purposes.

A brand telling you not to use its own headline number for dosing is worth stopping on. It may be the most honest sentence in the category.

Here is why it matters arithmetically. Take the PowerPanel MID and a target dose of 20 J/cm2, using the formula from dosage.

Using the solar figure of 158 mW/cm2: 20 × 1000 ÷ 158 = 127 seconds.

Using the spectrometer figure of 61 mW/cm2: 20 × 1000 ÷ 61 = 328 seconds.

If you set your timer from the solar number, you get about 39 percent of the dose you intended. On the Rouge Pro G4, timing from 164 rather than 90 gets you about 55 percent.

That gap is large enough to move you from inside the useful range to below the threshold. Under the biphasic dose response described by Huang, Chen, Carroll and Hamblin in Dose Response in 2009, that is the difference between an effect and nothing.

This is not only a consumer problem

The research literature has the same failure, which is worth knowing before assuming peer review protects you.

Hadis and colleagues reviewed measurement practice across the photobiomodulation literature in Lasers in Medical Science in 2016, in a paper titled "The dark art of light measurement". They found that 73 percent of the articles they reviewed contained no information about how light was measured and relied on manufacturer-stated values.

Their tally of missing parameters is worse than the headline. Power was missing in 41 percent of papers, beam area in 40 percent, irradiance in 43 percent, pulse frequency in 52 percent and radiant energy in 74 percent.

If published trials get this wrong at that rate, a product page has neither the incentive nor the equipment to do better.

The brands that publish both deserve credit

There is no regulation requiring any of this. No standard test method, no third-party audit, no penalty for publishing whichever number is largest. FDA clearance does not cover output claims either, as FDA cleared, registered or exempt explains.

In that environment, publishing a second number that makes your own product look weaker is a voluntary act against your commercial interest.

Mito Red, Block Blue Light and Rouge all publish both figures and name the instrument used for each. Block Blue Light goes further and tells you which one to use. That is the behaviour this category should reward.

How to read a single number

Most brands publish one figure and never name the instrument. Three rules help.

If no instrument is named, assume a solar meter. Nobody buys a spectroradiometer and then declines to mention it.

If you need a working estimate from a solar figure, halving it lands close to the observed range across the eight devices above. It is a rough correction rather than a measurement, but it beats the raw number.

Check whether a distance is stated. A figure with no distance is usually taken at the panel face and describes nothing you will experience. Why irradiance numbers are usually wrong covers the other ways these figures get inflated.

Then remember that irradiance is the least important variable here anyway. The sham-controlled mask trial that produced measurable results ran at 10 mW/cm2.

FAQ

Should I buy a solar meter to test my own panel? It is useful for one job: checking whether your panel's output is dropping over time, since a comparison against your own earlier readings on the same meter is valid. It will not give you an accurate absolute figure to calculate session length from.

Does a spectrometer reading mean the panel is weaker than advertised? It means the advertised figure included light that was never doing therapeutic work. The hardware is the same. Only the accounting changed.

Why does the ratio vary between 1.8 and 2.6? Panels differ in how much of their output sits in the stated therapeutic peaks rather than spread across other bands, and measurement conditions vary. A tighter ratio suggests more of the output is concentrated where the brand says it is.

Is a lower spectrometer number a reason to avoid a device? No. A device publishing 61 mW/cm2 honestly may deliver more useful light than one claiming 200 mW/cm2 with no instrument named. Compare spectrometer figures against other spectrometer figures, never across instruments.

Sources

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