Every irradiance number in this database carries one of three labels, and the label matters more than the number.

The three labels

Spectrometer means a laboratory-grade instrument measured the output across the wavelengths the panel actually emits. These figures are directly comparable with each other.

Solar meter means a handheld solar power meter was used. On LED panels these read roughly double what a spectrometer records, because they respond to a broader band of light than the panel emits, so a solar-meter figure is not comparable with a spectrometer figure.

Method not stated means the brand published a number without saying how it was measured. Treat it with caution and compare it only against other unlabeled figures.

What to do with the label

  • Compare spectrometer figures with spectrometer figures.
  • If a figure is solar-meter based or unlabeled, treat roughly half of it as the working value before calculating a dose.
  • Distance matters as much as instrument: a reading at 3 inches is not comparable with one at 6 inches, and the drop between them is not a simple straight-line scaling; the inverse square law explainer covers why a flat panel's falloff with distance behaves differently from a single point of light.
  • Panel size matters too: a small panel and a large panel can post nearly the same irradiance figure and still differ enormously in total output, since irradiance describes one point, not the whole panel.

How big the gap is in practice

The claimed vs measured study collects every panel in the database for which a brand claim and a spectrometer reading of the same panel both exist, 44 panels at the time of writing. Across them the claim runs a median 2.18 times the spectrometer figure, with the smallest gap at 1.36 times and the largest at 2.60. Thirty-eight of the 44 claims are solar meter figures, and 29 of the 44 are at least double the measured value. In several cases the brand publishes both numbers itself, side by side, which is why a "brand-published" figure can still carry the solar meter label.

A worked example

The BlockBlueLight PowerPanel MID is one of those dual-disclosure panels: 158 mW/cm2 by solar meter and 61 mW/cm2 by spectrometer, both at 6 inches, both from the brand. Put 158 into the dose calculator with a 10 minute session and it reports 94.8 J/cm2; put 61 in and it reports 36.6 J/cm2. Only the second figure describes the light reaching the skin, and only it belongs in a session plan. On this site the device page shows both numbers with their labels, and the spectrometer figure is the one the rankings use.

Where the label appears

On every device page the irradiance line reads as a triplet: the number, the instrument, and the distance, for example "61 mW/cm2, spectrometer, 6 in". The brand comparisons carry an "irradiance method" row so two brands can be checked against each other on the same footing, and the panel database lets you sort the whole list. A brand that publishes no method at all is shown as "method not stated" rather than being given a number it did not earn.

The pages linked below go deeper on each of these points.