If you were to remember one thing before buying an LED mask, it should be this.
The Two Numbers
mW/cm² — Irradiance. How much power reaches one square centimeter of skin at any given moment.
J/cm² — Fluence or total dose. How much energy that centimeter has received during the entire session.
The first is speed. The second is distance traveled.
The Formula
The relationship between the two is simple:
J/cm² = (mW/cm² × seconds) ÷ 1000
Or vice versa — if you know the desired dose and the power, you can calculate how long the session should last.
Example with Real Numbers
A device with 40 mW/cm², a session of 10 minutes (600 seconds):
(40 × 600) ÷ 1000 = 24 J/cm²
| Power | 10 min. | 20 min. |
|---|---|---|
| 10 mW/cm² | 6 J/cm² | 12 J/cm² |
| 25 mW/cm² | 15 J/cm² | 30 J/cm² |
| 50 mW/cm² | 30 J/cm² | 60 J/cm² |
You can see the problem with cheap devices: with very low irradiance, you would have to sit for hours to reach a therapeutic dose.
The Therapeutic Range
In the literature, most skin protocols generally fall within 1 to 60 J/cm², with irradiance between 5 and 50 mW/cm².
Both extremes matter. Too little has no effect. Too much can reduce the effect — this is the biphasic dose-response, described in how often.
Why the Diode Count Is Misleading
"280 diodes" sounds like a specification, but it's not. The count says nothing about:
- the power of each diode;
- the distance to the skin;
- the uniformity of coverage;
- how much of the emitted light actually penetrates the skin.
Two hundred weak diodes can deliver less energy than one hundred good ones. The only way to know is by measuring with a spectrometer or power meter.
That's why we publish the measured values for SpectraLift™ — up to 50 mW/cm². See also all LED face masks.
Frequently Asked Questions
How can I measure the power myself? You need an optical power meter. It's not a cheap device — it's more practical to request the data from the manufacturer.
What if the manufacturer doesn't specify mW/cm²? That in itself is an answer.
Is more mW/cm² always better? No. Above a certain level, heat appears, and the effect does not grow proportionally.
Related Articles
Sources
- Huang YY et al. Dose Response. 2009.
- Avci P et al. Semin Cutan Med Surg. 2013.
This article is for informational purposes only and does not substitute medical advice.
