Irradiance
Irradiance is the amount of optical power reaching a surface area, often written as mW/cm2. For buyers, it matters because it shapes dose only when the brand also explains measurement distance and test conditions.
What it means in plain English
Irradiance tells you how concentrated the light is at a given distance. A panel can look very strong on paper if the number was taken too close to the LEDs or under conditions you would never actually use at home.
Why buyers should care
If you are shopping for a red or near-infrared panel, irradiance helps you estimate whether the panel can deliver a believable dose in a realistic setup. Without distance and methodology, the number is incomplete.
How brands misuse it
Brands often highlight a large irradiance number without telling you the measurement distance, beam angle, or whether the reading was taken at the lens face. That makes one panel look stronger than another even when the real-use difference may be much smaller.