Joules are a measurement of energy. Joules per square centimeter (J/cm2) is the measurement of the amount of energy delivered to area of the body receiving light. Many recent studies state that joules may be the most critical parameter in evaluating the effectiveness of light therapy.
Most photobiomodulation is measured in milliwatts (mW) delivered per second. 1 Joule = 1000 milliwatts.