How much light does a red light panel really deliver? We measured the same Dermfix SLF1800 three ways, with a solar meter, a handheld spectrometer and an independent laboratory, and publish all three results here.
Panel: Dermfix SLF1800, all channels on at 100%, initial output, measured at the centre of the front surface, at 15 cm.
1. Solar meter
Many brands still quote solar meter readings for their panels. A solar meter is built to measure sunlight, not LEDs, so we find these figures misleading.
So we asked our colleague ZO-Lah! the Clown to take a reading for us, with a brand-new, factory-calibrated Tenmars TM-206A Solar Power Meter.
ZO-Lah!'s result
Poor ZO-Lah! failed in his mission. The meter showed "OL" (overload), meaning the reading was above its maximum of 200 mW/cm², before he got anywhere close to 15 cm.
ZO-Lah! says it was not his fault: we made him use a meter that was never designed for the job. He also stresses that this is in no way a fault of the Tenmars product, just a silly clown using it for the wrong purpose.
Brand new, with its factory calibration certificate
Still far away: 191.9
A step closer: OL
Solar meter readings at 15 cm
| Brand and panel | Solar meter (mW/cm²) | Source | Date checked |
|---|---|---|---|
| Dermfix SLF1800 | >200 (off the scale, "OL") | ZO-Lah! the Clown, Tenmars TM-206A | 16 Oct 2026 |
| Rojo Refine 180, 360, 1800 and 3600 | 195 | Rojo website (6″) | 9 Oct 2026 |
| Rojo Refine 900 | 185 | Rojo website (6″) | 9 Oct 2026 |
| heilys Gen300 | 182 | heilys Gen300 datasheet | 30 Sep 2026 |
| Koanna Luma1000 | 175 | Koanna website | 9 Oct 2026 |
| BlockBlueLight PowerPanel MEGA | 167 | BlockBlueLight website (6″) | 9 Oct 2026 |
| MITO LIGHT Mitohacker 5.0 | 165 | MITO LIGHT website | 30 Sep 2026 |
| MITO LIGHT Master 5.0 | 165 | MITO LIGHT website | 30 Sep 2026 |
| Rouge Pro G4 | 164 | Rouge website (6″) | 9 Oct 2026 |
| BlockBlueLight PowerPanel PRO | 160 | BlockBlueLight website (6″) | 9 Oct 2026 |
| MITO LIGHT Biohacker 5.0 | 145 | MITO LIGHT website | 30 Sep 2026 |
| MITO LIGHT Expert 5.0 | 140 | MITO LIGHT website | 30 Sep 2026 |
| Hooga ULTRA360 | 136 | Hooga website (6″) | 9 Oct 2026 |
ZO-Lah! finally finds something his meter can measure: sunshine.
* Solar power meters such as the Tenmars TM-206A are designed for measuring sunlight, not narrow-band LED arrays. Where a brand doesn't name its meter, we've assumed a solar meter. Nothing else we know of gives readings that high.
2. Hopoocolor OHSP-350IR spectrometer
| Distance | Total irradiance (mW/cm²) |
|---|---|
| 15 cm | 89 |
| 30 cm | 82 |
Next, we measured the same panel, at the same spot and distance, with our Hopoocolor OHSP-350IR. This is a big step up from a solar meter. It is a true spectrometer: it records the actual spectrum of the light, so it shows how much output falls in red and how much in near-infrared. It is also the instrument many reviewers and social media influencers use to show panel results.
It still has limits, and if used incorrectly it can give misleading numbers.
You will find spectrometer results like these published for many panels on the market. They are more useful than solar meter figures, but they are not from an independent laboratory, so they are still hard to verify. Our own reading is no exception, which is why we also sent the panel to a lab.
OHSP-350IR sample readings
Our OHSP-350IRF, with its manual and factory QC certificate
3. Independent laboratory
Red light therapy has become an arms race of marketing claims, with every brand trying to show the most flattering figure. Dermfix has over 20 years' experience designing and making medical phototherapy devices, and honestly, we've been a little surprised by some of the figures we see. We're trying to do things differently. We won't get everything right, and our panels may not suit every user, but every figure we publish is one we can back up.
So before you get to the numbers, here's what was measured, and why.
Who measured it
We didn't measure it ourselves. We left that to LightingLab Calibration Laboratory Ltd. in Veszprém, Hungary, a calibration and testing laboratory accredited to ISO/IEC 17025 by the Hungarian National Accreditation Authority (NAH). There are many types of professional equipment and many ways to set them up, and the results are surprisingly sensitive (even room temperature matters).
How it was measured
- Distance: 15 cm (6 inches) seems to have become the industry's standard measuring distance, but there's no regulation behind it. The safety standard we test to, EN 62471, assesses many light sources at 20 cm, but only to set a product's risk group, not to tell you how far away to sit. We measured at 15 cm so you can compare us with others, and at 30 cm, which is closer to how most people actually use a panel.
- Initial and sustained output: some standard tests define a warm-up period of 20 minutes or more, but nobody runs their panel for 20 minutes before using it. So the lab measured the initial output, as soon as the panel is switched on, and the sustained output after 10 minutes, typical of a real session.
- One fixed point: every reading was taken at the same spot, the centre of the panel, so all the numbers can be compared with each other.
What was measured
- All wavelengths together, at 100%: the light that actually reaches your skin, at 15 cm and 30 cm, initial and sustained (after 10 minutes). Those four figures are the ones we publish.
Why we don't add the single wavelengths together
Some brands measure each wavelength on its own, directly in front of its own LEDs, and add the results together to quote a bigger number. We don't, because:
- Each best-case reading is taken directly in front of that wavelength's own LEDs.
- The different LEDs are spread across the panel, and each has a narrow 30° lens, so any one spot on your skin is lit mainly by the LEDs closest to it.
- Your skin never receives the best case of all seven wavelengths at the same spot at the same time. Adding them up gives a number no one can measure in front of the panel, and no one ever receives.
And integrating spheres?
You may also see "integrating sphere" figures, and they're becoming fashionable. A sphere captures all the light a panel emits in every direction: its total output in watts. That's a real number, but it tells you nothing about how much light actually reaches your skin at 15 or 30 cm.
A sphere counts every bit of light the same, whether it's aimed straight at you or sprays out sideways into the room. So a panel that wastes much of its light can score just as well as one that puts it all where you're sitting. It's a bit like judging a shower by how much water goes down the drain, not how much lands on you.
And it gets worse. We have even seen competitors take those sphere numbers and extrapolate them into an irradiance figure for the user. That's a calculation, not a measurement: no sensor was ever placed where your skin would be.
Using the figures
The all-wavelength figure at 15 cm or 30 cm is the light that actually reaches your skin. If you like to work out Joules, that's the one to use.
And here's the part we're most proud of: step back from 15 cm to 30 cm and our panel keeps 89% of its output, both initial and sustained. That's no accident. The SLF1800's 30° lenses focus the light forward instead of spraying it sideways, so the intensity holds as you move back. In practice, that means you can sit at a relaxed, comfortable distance, cover far more of your body in one session, and still get almost 90% of the dose. We think that matters far more than any single headline number.
Our honest conclusion
Panel figures are complicated, and some of the numbers out there aren't much help when you're trying to choose. We're a small family business and we're not chasing quick sales. We've made and sold our own certified medical UVB phototherapy devices for over 17 years, and we take our reputation seriously.
The good news is that red light has a large and growing body of research behind it: PubMed, the US National Library of Medicine's database, lists over 12,000 articles on photobiomodulation (the scientific term for red and near-infrared light therapy). For a wellness device, regular use matters more than chasing exact figures, distances or Joules. So our ultimate advice is simple:
Relax, enjoy your red light, and make it a regular habit.
Independent laboratory measurement — Dermfix SLF1800
| Distance | Initial output | Sustained output (after 10 minutes) |
|---|---|---|
| 15 cm | 83.3 mW/cm² | 74.0 mW/cm² |
| 30 cm | 73.8 mW/cm² | 65.7 mW/cm² |
Irradiance with all channels at 100%, measured perpendicular to the panel at its geometric centre. Measured on 2 November 2026 by LightingLab Calibration Laboratory Ltd., Veszprém, Hungary, accredited to ISO/IEC 17025 (NAH-2-0368/2023). Calibration certificate LL-26-6174. Expanded measurement uncertainty ±2.3% (k = 2).
Summary: three ways to measure a panel
| Measurement method | Who uses it | Suitability for LED panels | Typical result at 15 cm |
|---|---|---|---|
| 1. Solar power meter | ZO-Lah! the Clown, and a few others :-) | Not suitable. Built and calibrated for sunlight, not narrow-band LEDs | Inflated: 136 to over 200 mW/cm² |
| 2. Handheld spectrometer | Reviewers, influencers and brands, including us | Moderate. Real spectrum, but results depend on the user and the unit's calibration | 89 mW/cm² (our OHSP-350IR), not independently verified |
| 3. Accredited laboratory | Dermfix, via LightingLab | Reference standard. Calibrated spectroradiometer and reference detector, traceable to national standards | 83.3 mW/cm² initial, 74.0 sustained (after 10 minutes) (LightingLab, certificate LL-26-6174) |
For how the SLF1800 compares with other panels sold in Europe, see our best red light therapy panel in Europe 2026 guide.