Red light therapy panels are now everywhere — from handheld devices to full-body panels.
Nearly all of them advertise numbers like “100 mW/cm²”.
But very few users — and often not even the manufacturers — actually know whether that number is true at the point where the light reaches the body. In practice, most people are making treatment decisions based on numbers they cannot verify. The panel specification may be measured at a different distance, under ideal conditions, or when the LEDs were new. Without a reliable way to measure irradiance at the treatment location, the actual optical dose reaching the body is largely unknown. The result is that two people using the same panel may be receiving dramatically different doses of light.
The measurement gap
Tools that attempt to measure light output fall into three categories:
Lux meters
Lux meters measure illuminance, a quantity weighted for human vision.
They are designed for lighting design, not energy measurement. For red and near-infrared wavelengths, lux readings have little relationship to actual optical power.
Laboratory radiometers
Professional optical power meters measure irradiance directly and accurately.
However, they typically cost thousands of dollars and require either:
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prior knowledge of wavelength, or
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a spectrometer to determine it.
Because photodiode responsivity varies strongly with wavelength, incorrect spectral assumptions can produce large errors.
Low-cost “irradiance meters”
A number of consumer instruments claim to measure mW/cm² across multiple wavelengths.
In practice, their calibration is rarely traceable, and spectral correction is often crude. When compared against a laboratory-grade Thorlabs optical power meter, the units I tested differed by more than 50% at common red-light therapy wavelengths.
Why dose calculation is harder than it looks
Optical dose — measured in J/cm² — is the central parameter in photobiomodulation research. But getting irradiance right requires more than a single photodiode behind a window.
Irradiance varies rapidly with distance from an LED panel — a few centimeters makes a meaningful difference. It varies with angle — a meter held even slightly off-axis underreads. And photodiode responsivity is wavelength-dependent, which means a reading taken without knowing the spectral content of the source carries an unknown calibration error. A 630 nm panel and a 660 nm panel look similar to an uncorrected photodiode but require different calibration factors to produce accurate mW/cm² values.
As an example of why this matters:
- Optical dose is expressed in J/cm², which is simply irradiance multiplied by time.
- A panel delivering 40 mW/cm² produces a dose of 2.4 J/cm² per minute.
- But if the irradiance measurement is wrong by 50%, the resulting dose calculation is also wrong by 50%.
Getting a trustworthy number requires knowing the spectrum, the distance, the angle, and having a calibration traceable to a recognized reference standard. No consumer device currently provides all of this together.
What we’re building
The OptiVerity Puck — the name combining ‘optical’ and ‘verity,’ meaning truth — is a portable spectral irradiance meter designed to close this measurement gap. While the immediate application is red light therapy validation, the same problem exists wherever actual optical energy at a surface matters: LED engineering, grow lighting, and optical product verification all share the same lack of accessible, accurate measurement tools.
The device integrates several measurements that normally require multiple instruments:
| Measurement | Purpose |
|---|---|
| Calibrated irradiance | Accurate mW/cm² measurement using a cosine-corrected PTFE diffuser |
| Spectrum | Multi-channel spectral sensing to determine wavelength and apply responsivity correction |
| Distance | Time-of-flight ranging to document measurement geometry |
| Tilt | IMU orientation sensing to validate cosine response |
| PWM detection | High-bandwidth photodiode path detects LED modulation and flicker |
| Calibration | Traceable reference calibration against a laboratory radiometer |
Using the device is intentionally simple.
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Hold the puck against the panel surface and press the button.
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Move the puck to your treatment distance and press again.
The companion software reports:
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Irradiance at the treatment point
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Dominant wavelength
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Distance and angle
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PWM modulation characteristics
From irradiance and exposure time, optical dose follows directly.
Project status
The OptiVerity Puck is currently in active development.
The schematic is largely complete, PCB layout is underway, and a small prototype batch is planned as the first milestone. Calibration will be performed against a NIST-traceable Thorlabs reference sensor.
The goal at this stage is to share the development process openly and invite feedback from the community.
If you work with photobiomodulation, horticulture lighting, or LED measurement and have thoughts on what a device like this should do, I would love to hear from you.
Follow the development or get in touch through the contact page.