Irradiance, joules, fluence — the technical terms behind light therapy dosage, decoded in plain English so you can judge any device with confidence.
If you want to evaluate an LED device like a pro, a little dosage vocabulary goes a long way. These are the numbers behind the results.
Irradiance (mW/cm²)
Irradiance is the power of light hitting a given area of skin — essentially how 'bright' the therapeutic light is at the surface. It is the rate at which energy is delivered.
Dose or fluence (J/cm²)
Multiply irradiance by time and you get the dose, measured in joules per square centimeter. This total energy delivered is what your cells actually respond to. A common therapeutic window falls between roughly 5 and 30 J/cm² per session.
Why the session length is set
Device makers calibrate session length around their irradiance so you land in the therapeutic window automatically. This is why following the recommended 15-minute session matters — it is engineered to deliver the right dose.
More is not better
Because of the biphasic dose response, stacking on extra time will not multiply your results. Trust the recommended session and prioritize consistency instead.
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