A red light therapy device is a panel or lamp that shines red or near-infrared light on the skin. Prices run wide, and the sales copy is loud. The spec sheet is quieter and far more useful. Here are the four things worth comparing.
Wavelength: read the numbers, not the color
Wavelength is measured in nanometers (nm). Panels usually list a red peak, a near-infrared peak, or both. A review by Michael Hamblin in AIMS Biophysics (2017) describes red as 600 to 700 nm and near-infrared as 770 to 1,200 nm. It notes a gap between 700 and 770 nm where results are likely to be disappointing.
So check the listed peaks. A label that says only "red light" or "full spectrum" tells you little. Look for exact nanometer figures, ideally with the tolerance, such as "660 nm, plus or minus 10."
Sources: Hamblin MR, "Mechanisms and applications of the anti-inflammatory effects of photobiomodulation," AIMS Biophysics 2017;4(3):337-361 (PMC5523874).
Irradiance: the number most pages skip
Irradiance is power per area, in milliwatts per square centimeter (mW/cm2). It tells you how strong the light is at a given spot. A spec without a distance is not usable, because light weakens as you move away. A fair listing says something like "mW/cm2 measured at 6 inches."
The same review shows why this matters in the research. It describes a rat study in which a one-minute exposure at 50 mW/cm2 was not effective, while longer exposures worked about as well as each other. The lesson is that power and time work together. It also explains the "biphasic dose response": there is an optimum dose, and too much light can work worse than less. That is a reason to be wary of "more watts" as a selling point. This guide makes no claims about what any dose does for a person.
Watch the headline wattage too. The "total power" a maker lists is often the electrical draw of the unit, not the light that reaches you. Ask for measured irradiance, and note whether it came from the maker or an independent lab.
Sources: Hamblin MR, AIMS Biophysics 2017 (PMC5523874).
Size and layout: what you can actually cover
Panel size sets how much of your body sits inside the light field. A small handheld unit covers a patch. A large panel covers more, but costs more and needs wall or door mounting. Compare these listed facts:
Panel dimensions and weight. Number of LEDs and how they are spaced. Whether the beam is flat or angled. Cord length, timer and stand options. Whether near-infrared and red can be switched separately.
Also check heat and eye safety notes. Bright LEDs can be hard on the eyes, so look for a manual that mentions eye protection and a clear usage-time limit.
FDA wording: what the label can and cannot say
In the United States, light therapy products sit in two lanes. The first is a cleared medical device. FDA's January 2023 draft guidance on photobiomodulation (PBM) devices, also called low-level light therapy, covers class II devices that go through a 510(k) premarket notification. It is a draft, so it is not final, and it says some light-emitting products meant only for general wellness may fall outside its scope.
The second lane is general wellness. FDA's guidance "General Wellness: Policy for Low Risk Devices" (September 2019) says the agency does not intend to examine low risk products meant only for general wellness. The policy applies only to low risk products. FDA's list of what is not low risk includes products that raise risks "from lasers or radiation exposure," and it gives a laser product as an example.
What does this mean at the shelf? A product marketed for general wellness cannot lean on disease claims. A product that names a disease or condition in its marketing is making a different kind of claim. If a seller says "FDA cleared," ask for the 510(k) number and the cleared indication. FDA keeps a public 510(k) database you can search. Do not accept "FDA registered" as the same thing. Registration is not clearance.
Sources: FDA, "Photobiomodulation (PBM) Devices - Premarket Notification [510(k)] Submissions," draft guidance, January 2023; FDA, "General Wellness: Policy for Low Risk Devices," guidance, September 2019.
A short checklist before you pay
Use this list on any listing you read. Exact nanometer peaks, with tolerance. Irradiance in mW/cm2, with the distance. Who measured it. Real dimensions and the area covered. Eye safety and usage-time guidance. A 510(k) number if "cleared" is claimed, or a plain general wellness label if not. A clear return window and warranty.
Skip any listing that promises a result for a disease or a body part. Specs can be checked. Promises cannot. A seller that gives you the numbers is easier to trust than one that gives you adjectives.
Sources: as listed above.