Irradiance explained: the spec nobody publishes
Dose is irradiance times time. Irradiance is measured in mW/cm² at a stated distance — and across every panel we surveyed, at every price, not one published it.
If you read one page in this hub, read this one. Irradiance is the specification that determines what a red light panel actually does, and it is the specification the entire consumer category declines to publish.
What irradiance is
Irradiance is power per unit area — how much light energy lands on each square centimeter of your skin per second. It is measured in milliwatts per square centimeter, mW/cm².
Dose is irradiance multiplied by time, and it is usually expressed in joules per square centimeter (J/cm²). So if you know a panel's irradiance at the distance you stand, you can calculate how long a session needs to be to reach a given dose. That is the whole point of the number.
| Quantity | Unit | Meaning |
|---|---|---|
| Irradiance | mW/cm² | Power arriving per square centimeter |
| Time | seconds | How long you are exposed |
| Dose (fluence) | J/cm² | Irradiance × time ÷ 1,000 |
Worked example: a panel delivering 50 mW/cm² for 200 seconds gives 50 × 200 ÷ 1,000 = 10 J/cm². Without the first number, none of this arithmetic is available to you.
Why distance dominates
Light from a source spreads out as it travels, so the energy landing on any given square centimeter falls as you move away. That means an irradiance figure without a stated distance is meaningless — it could be a reading taken with a meter touching the panel, or one taken at arm's length, and those are wildly different numbers for the same device.
This is the same problem as sauna EMF figures, and it recurs for the same reason: a number without its measurement conditions can be technically true and practically useless.
What we found
We surveyed the red light panels available through mainstream retail and looked for an irradiance figure with a stated measurement distance.
| Panel | Irradiance figure | Stated distance | Usable? |
|---|---|---|---|
| Full-body dual chip | Not published | — | No |
| Supersred 36×8 | Not published | — | No |
| EXESAS 400 W | Not published | — | No |
| BestQool Pro200 | Not published | — | No |
| Cabpay 45 W | Not published | — | No |
Compiled 2026-09-07 from the sellers' own published listings. Zero of five publish an irradiance figure. What they publish instead is wattage — and that wattage is an LED rating rather than measured consumption, and neither figure tells you what reaches your skin.
Why wattage is not a substitute
Three separate problems with treating advertised wattage as a proxy:
- 1It is an LED rating, not consumption. A panel advertised at 1,500 W does not draw 1,500 W from the wall. It is the sum of the diodes' nominal ratings.
- 2Electrical input is not light output. LEDs convert some of their input to light and the rest to heat, and the efficiency varies by design and by how well the panel manages its own temperature.
- 3Output is not delivered dose. Light spreads. A high-output panel at three feet may deliver less to your skin than a modest one at six inches.
Each step loses information, and the three together mean wattage tells you roughly how big a panel is and essentially nothing else.
How to buy without the number
- 1Ask. "What is the irradiance in mW/cm² at 6 inches?" is a specific, answerable question. Send it before you buy. A company that answers with a number and a distance is offering something rare; one that answers with wattage is not answering.
- 2Control distance yourself. This is the variable in your hands. Closer means more per minute, whatever panel you own — which is also the honest argument for a standalone panel over a fixed sauna tube.
- 3Follow the manufacturer's session guidance, which at least reflects their own assumptions about their own device.
- 4Buy on what is published: wavelength, dual chip, board area, flicker specification. Those are real and checkable.
- 5Be skeptical of extraordinary wattage claims on small boards. The arithmetic rarely works.
Can you measure it yourself?
Consumer solar power meters are sometimes used for this and they will give you a reading. Two honest caveats: they are calibrated for broadband solar spectrum rather than for narrow-band LED output, and they respond differently across wavelengths — so a reading from one is indicative rather than accurate, particularly for the 850 nm component.
What such a meter *is* genuinely good for is relative measurement: comparing the same panel at 6 inches and 18 inches shows you how sharply irradiance falls off in your setup. That is useful information even if the absolute number is not trustworthy.
Why this matters more than any other spec
Photobiomodulation research specifies doses. A study that found an effect found it at a particular irradiance for a particular time. Without knowing your panel's irradiance, you cannot tell whether you are in the same range, an order of magnitude below, or well above.
That is the honest state of consumer red light therapy: the products emit the right wavelengths and nobody can tell you the dose. We would rather say that plainly than rank panels as though the missing number did not matter.
Questions people actually ask
What is irradiance in red light therapy?
What irradiance should a red light panel have?
Does wattage tell you the irradiance?
How far should I sit from a red light panel?
Can I measure red light irradiance with a solar meter?
Sources
Read next
Every pick on this page comes from published specifications, not from hardware we own. Read how we pick — including what spec-led ranking cannot tell you.