Solar Light’s Model PMA2123 Digital Bilirubin Phototherapy Sensor is an accurate, stable sensor designed to measure the output of phototherapy lamps used in neonatal wards to treat infant hyperbilirubinemia (jaundice.) Blue light in the spectral range of 425-475 nm chemically alters bilirubin below the surface of the skin into byproducts that an infant can eliminate in urine. The standard PMA2123 sensor has a narrow spectral response from 425-475 nm, closely matching the action spectrum for bilirubin breakdown. The measurement will be accurate for the output of any lamp, especially the blue fluorescent, daylight fluorescent, and quartz halogen lamps commonly used in bililight units. The PMA2123 sensor is calibrated to read in µW/cm2. The angular response of the PMA2123 sensor is cosine corrected, and suitable for measurements of diffuse radiation or radiation from extended sources.