Irradiance (mW/cm2)
Quick definition
Irradiance is the intensity of light hitting your skin, measured in milliwatts per square centimeter.
The Science
Think of irradiance like water pressure in a shower. Higher irradiance means more light energy is reaching the skin in each second. Too little and the session may be too weak to do much. Too much and you can create unnecessary heat or discomfort instead of a well-controlled home treatment.
Why it matters for your skin
Ignore vague marketing claims about total watts or LED count. For home masks, irradiance helps you judge whether the device is likely to deliver a meaningful dose in a realistic session length.