In this study, we investigated the four type of measurement methods to the irradiance of the medical LED light source by using portable optical wave meter and goniophotometer. As a result, the variation rate of irradiance according to the measurement equipment and measurement methods ranged from -44% to 371%, the variation rate of irradiance increased as the beam angle became smaller, or as the light distribution becomes more deviated. This study calculated the beam angle irradiated in the cell plate through the proposed measurement method using the radiant flux (Wθ) within the half angle (θ), and further calculated the irradiance (EWθ) by dividing the Wθ measured through the goniophotometer by the floor area of the cell plate. The proposed measurement method showed no deviation of the data according to the performance of the light source itself, including the beam angle, and provided the irradiance directly incident on the cell. Furthermore, because the horizontal illuminance is used for the luminous flux incident on the irradiated area in the conventional LED test standard, this study confirmed that the use of the radiant flux is more advantageous in obtaining the traceability between measured data than the radiant intensity.