An LED mask box usually gives you three numbers: a wavelength in nanometres, a count of LEDs, and a session length in minutes. Only one of them describes what the light does to your skin, and it is not the one most boxes print largest.
- Device
- LED face mask or panel
- Time
- 5 minutes to read
- Tools
- The manual for your model
- Difficulty
- No disassembly
Nanometres: the colour, and nothing else
The nanometre figure is the wavelength of the light. It is a precise way of saying what colour the LED emits, and different wavelengths reach different depths of skin. Red light around 630 nanometres and near-infrared around 830 are the two most commonly printed on consumer masks; blue light sits near 415.
What the number does not tell you is how much light arrives. Two masks can both say 630nm and deliver very different amounts of energy, because wavelength describes colour and says nothing about intensity or duration.
The count of LEDs tells you less than it looks
A mask advertising 150 LEDs is not necessarily brighter than one with 100. It depends on the output of each diode, how far they sit from skin, and how evenly they are spread. A high count arranged badly can leave the sides of the face receiving noticeably less than the centre.
Treat the count as a rough proxy for coverage, not for power.
The figure that matters is rarely on the box
- Irradiance How much light reaches a given area of skin, usually in milliwatts per square centimetre. This is the closest thing to a power rating, and it is the number that determines how long a session needs to be.
- Dose Irradiance multiplied by time, expressed in joules per square centimetre. It is the honest way to compare two devices — and the reason a longer session on a weaker mask can deliver the same dose as a shorter one on a stronger mask.
- Distance Light falls off sharply with distance. A panel held at arm’s length delivers a small fraction of what the same panel delivers resting against skin. If a manufacturer specifies a distance, that specification is part of the dose.
- Session length and frequency Manufacturers set these to match their own device’s output. Numbers borrowed from a different mask, or from a clinic device, do not transfer.
If a manufacturer publishes irradiance and the distance it was measured at, that is a meaningful specification. If the box lists only wavelength and LED count, you cannot work out the dose from what you have been given.
What the evidence supports, and what it does not
The American Academy of Dermatology notes that some visible-light LED devices have been cleared by the FDA for home use, and that home devices are less powerful than the equipment a dermatologist uses. That difference in power is the practical point: a weaker device is not necessarily useless, but it will not reproduce clinic results on a clinic timetable.
For acne specifically, the AAD notes that blue and red light can help with pimples, while visible light does not address blackheads, whiteheads, cysts or nodules. A device that promises to clear all forms of acne is promising more than the category supports.
Reading a box quickly
Look for a wavelength with a tolerance (“630nm ± 10”) rather than a bare number, an irradiance figure with the distance it was measured at, and a session length tied to that device rather than a generic recommendation. A box that gives all three is describing a measured product. A box that gives none is selling a colour.
Sources
- Is red light therapy right for your skin? — American Academy of Dermatology
- Lasers and lights: how well do they treat acne? — American Academy of Dermatology
- Medical lasers — U.S. Food and Drug Administration