Photobiomodulation does not follow a simple, linear dose-effect relationship where more is always better. Published research consistently demonstrates a biphasic dose-response curve rooted in the Arndt-Schulz Law: a low stimulus excites biological activity, a moderate stimulus reaches peak effect, and an excessive stimulus suppresses it.

The key metric is fluence, measured in Joules per square centimeter (J/cm²), which equals irradiance (mW/cm²) multiplied by exposure time. Commercial protocols are designed to deliver a dose within the therapeutic window, not to maximize exposure time. Understanding this helps salon operators evaluate why a calibrated session of a defined length outperforms an arbitrary one.

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