Why manufacturer irradiance claims run 30–60% high

Verdict: derate every spec-sheet irradiance number by 30–60%

Manufacturer irradiance numbers are systematically inflated. Not by conspiracy — by two mechanical causes that compound: solar power meters over-read LED panels, and brands publish the most favorable measurement they can defend (peak spot, closest distance). Independent testers consistently measure 30–60% below claimed irradiance across the category (ev010).

Treat every spec-sheet irradiance as an upper bound, not a treatment parameter. If you're doing dose math from a manufacturer number, derate it by 30–60% before you calculate your session time. If independent measurement exists for your specific device, use that instead.

We'll show you why this happens, walk the math, and tell you what to do about it.

The two mechanisms

1. Solar meters over-read LEDs

The standard tool for measuring light panel irradiance is a solar power meter — the kind designed to measure sunlight hitting a solar panel. These meters are calibrated for a broad-spectrum solar source, not for narrow-band LEDs. When you point one at an RLT panel, it over-reports the irradiance because the spectral response curve doesn't match the LED output (ev010). The meter reads higher than what's actually arriving at your skin.

This isn't a brand lying — it's a measurement instrument used outside its calibration. But it is the instrument most brands use to generate the number on the spec sheet.

2. Peak-spot publishing

Even with a correct instrument, there's a second problem: where you point it. LED panels don't produce uniform irradiance across their surface. There are hot spots and cool spots. Brands measure the hot spot — the peak irradiance point — and publish that number (ev010).

If your panel claims 100 mW/cm² [claimed] at 6 inches, that's the best-case reading at the brightest point on the panel face. Move the meter two inches sideways and the number drops. Move it to a corner and it drops further. The number on the box is the ceiling, not the average.

Why distance makes it worse

Panel irradiance falls off steeply with distance. This isn't a clean inverse-square law — panels are extended sources, not point sources — but the practical rule of thumb holds: double your distance and you get roughly half or less irradiance in the near field (ev020).

Most brands quote irradiance at 6 inches (ev021). Joovv quotes at 12 inches, which makes their numbers look lower on paper relative to competitors — but also means a Joovv panel at 6 inches delivers more than its spec sheet suggests, while a competitor quoted at 6 inches delivers less at 12 inches. Cross-brand spec comparison without distance normalization is meaningless (ev021).

The worked example

Here's what this does to your dose math. The dose formula is:

J/cm² [estimated] = mW/cm² [estimated] × seconds / 1000 (ev018)

Scenario: A panel claims 100 mW/cm² [claimed] at 6 inches. You want a 10 J/cm² [estimated] dose at the skin surface. The naive calculation:

10 J/cm² [estimated] = 100 mW/cm² [claimed] × seconds / 1000 seconds = 10 × 1000 / 100 = 100 seconds [estimated]

You'd set a 100-second timer and think you're delivering 10 J/cm² [estimated]. But if independent measurement shows the actual irradiance at 6 inches is 55 mW/cm² [measured] — a 45% reduction, squarely in the 30–60% range (ev010) — your real dose is:

55 mW/cm² [measured] × 100 s / 1000 = 5.5 J/cm² [estimated]

You got 5.5 J/cm² [estimated], not 10. You're under-dosing by nearly half.

The fix: derate the claimed number before doing the math. If no independent measurement exists for your device, apply the category-wide 30–60% haircut (ev010) and use the midpoint as a working estimate:

Derated irradiance = 100 mW/cm² [claimed] × 0.55 = 55 mW/cm² [estimated] Session time for 10 J/cm² [estimated] = 10 × 1000 / 55 = 182 seconds [estimated]

That's nearly double the naive time. Same panel, same target dose, very different session length.

The measurement coverage gap

Here's the uncomfortable part: independent irradiance and spectral measurement exists for only a few dozen devices out of hundreds on the market (ev017). Alex Fergus at Light Therapy Insiders is the community's de-facto independent measurement auditor (ev015), but even his coverage is a fraction of the category. Most panels have never been independently tested.

This means for most devices, you cannot look up a [measured] number. You're stuck with [claimed] and the category-wide derate. That's not ideal, but it's honest — and it's better than trusting a number calibrated to a solar meter pointed at a hot spot.

What this means for your dosing

The PBM literature reports effective doses roughly in the 3–60 J/cm² [measured] range at tissue surface depending on the target, with no single agreed number (ev019). The literature also documents a biphasic dose response: beyond a certain threshold, more is not better — it may be worse (ev013). Exact thresholds per condition are not established, and we will not publish a universal optimal dose (ev013).

What this means practically: if your dose math is built on an inflated irradiance number, you might be landing in the effective range by accident — your 100-second session targeting 10 J/cm² [estimated] is actually delivering 5.5 J/cm² [estimated], which is still in the literature's effective band (ev019). Or you might be under-dosing below the evidence range. You can't know without a real measurement.

This is also why "more power" is a poor spec-war axis. The biphasic dose response (ev013) means the panel with the highest irradiance isn't necessarily the best — it's the one that lets you hit a target dose accurately. And you can't hit a target accurately with a number that's 30–60% wrong.

What to do

  1. If independent measurement exists for your device: use the [measured] irradiance figure for your distance. Stop reading the spec sheet. The spec sheet is marketing; the independent test is data.
  2. If no independent measurement exists: derate the [claimed] irradiance by 45% (the midpoint of the 30–60% range) before doing dose math (ev010). Tag every number you produce from this as [estimated], because that's what it is.
  3. Normalize for distance before comparing brands. A panel quoting 100 mW/cm² [claimed] at 6 inches and a panel quoting 80 mW/cm² [claimed] at 12 inches are not directly comparable. Derate both to the same distance using the near-field falloff rule (ev020) before you compare.
  4. Don't chase peak irradiance. The biphasic dose response means more power isn't better past a threshold (ev013). A panel you can dose accurately from a [measured] number beats a panel with a bigger [claimed] number and no verification.

Who should NOT use this page

If you're not doing dose math — if you just sit in front of your panel for 10 minutes because it feels good and you're not tracking a specific condition endpoint — the irradiance inflation doesn't change your protocol. The 30–60% gap matters when you're trying to hit a target dose in J/cm² [estimated]. If you're not targeting a dose, this page is background you don't need to act on.

The bottom line

The spec sheet is the ceiling. The ceiling is 30–60% above the floor. Until independent measurement coverage expands beyond the current few dozen devices (ev017), the category-wide derate is the honest default. Use it.