Energy Exposure

H_e, the ratio of the energy dQ_e incident on an element of an exposed surface to the area dA of the element. An equivalent definition is that energy exposure is the product of the irradiance E_e and the length of exposure dt. Energy exposure H_e = dQ_e/dA = ∫E_e dt, and it is measured in joules per square meter (J × m^–2). The quantity analogous to energy exposure in the system of photometric quantities is called exposure.