Jaundice (hyperbilirubinaemia) is a condition in which the skin turns a yellowish colour due to the presence of high levels of bilirubin in the blood. Treatment is usually by phototherapy: exposing the skin to blue-coloured light with a peak wavelength range of 450 nm to 460 nm.

There are two main problems with the calibration and use of the radiometers designed to measure this optical radiation. First, there is no standardised optical radiation source for the treatment, and no standardised spectral responsivity function for the instruments. Second, the instruments themselves often incorrectly display measurements in the units of spectral irradiance (µW·cm^-2·nm^-1) rather than broadband irradiance (µW·cm^-2).

This paper provides a review of the development of the action spectrum used in the treatment of jaundice and outlines the main problems encountered by calibration laboratories and users of the instruments. Good agreement between calibration laboratories when using a controlled source spectrum is demonstrated.