Irradiance (mW/cm²) is the speedometer; fluence (J/cm²) is the odometer — you need both. Use J/cm² = mW/cm² × seconds ÷ 1000 to calculate true dose. Demand wavelength-separated readings, grid measurements, spectroradiometer data, and stated distance. Higher power isn't better: photobiomodulation follows a biphasic dose response with an optimal window.