Hyperbilirubinemia Hyperbilirubinemia is a pathologic process consisting of the abnormal increase of the amount of bilirubin in the circulating blood, which can cause jaundice. A common treatment is expose the premature newborn to the phototherapy treatment, with lamps that emit in a specific region of the electromagnetic spectrum (mainly 410-550 nm). In the present work we describe one irradiance analysis method to this type of bilirubin lamps (in the case a Phillips TL20W/52), based on the determination of the intensity variation as a mathematical function depends on time (hours) with which we can simulate this behavior. We used the Exhaustive Approximation method combined with the Distinguish region-curve method for the determination of the corresponding function. Also, we compare the spectral irradiance of the lamp, with the solar spectral irradiance measured with a high quality double monocromator Optronic 756 spectrorradiometer, the day October 26 of 2012, at 12:49 local hour, in Rosario, Argentina. As a consequence, it was observed that the lamp intensity is very small compared with the solar one, which means that a careful analysis of the solar radiation incident on a given place needs to be made, if a treatment with natural radiation would be used for bilirubin reduction.