In the literature the irradiance of light-curing units (LCUs) is usually measured and expressed in watt per square centimeter (Wcm −2 ) or as spectral irradiance with arbitrary units. However, neither situation measures how the broadband really interacts with the substrate. For the correct dosimetry of such sources, it is necessary to evaluate the spectral distribution of their irradiance, also called spectral irradiance, which has units of Wcm −2 nm −1 . Here, the theory of optical dosimetry with respect to dental light-cure composite resins is revised; moreover, experimental determination of the optical dosimetry of composite resins cured with light-emitting diode (LED) sources is reported, including all of the substrates participating in the curing processes, especially the adhesive agent, as well as adjacent tissues like the enamel and dentine. A review of the literature showed that a casual use of different radiometric quantities and units is observed. This encompasses many types of mistakes and gives rise to dubious interpretation of the published results. We strongly recommend that interdisciplinary coworkers solve this kind of problem before publication and provide additional reliability and accordance with internationally assigned radiometric quantities and units as published by the Bureau International des Poids et Mesures and the International Union of Pure and Applied Chemistry (IUPAC).