The Challenge to Accurately Measure Irradiance

In a seminal report, about fifty years ago, Cremer, et al.(1) defined the basic principles of phototherapy as the spectral distribution for the photo-destruction of bilirubin (action spectrum ~ 400-520 nm), the effect of light intensity on the rate of bilirubin photo-degradation in vitro (t1⁄2=23 minutes, for sunlight) and the in vivo rate of bilirubin decline (–1.0 to 3.5 mg/dL/h or –17 to 60 μmol/L/h) under sunlight. Realizing that the use of sunlight phototherapy entailed various strategic and clinical disadvantages, they proceeded to investigate the more easily controlled light from artificial light sources. Thereupon, the first artificial light device, with strategically placed reflectors, was thoughtfully developed. Using eight closely spaced blue (B) fluorescent tubes, they studied the first overhead treatment of newborns in a cradle. This device demonstrated a very significant and satisfactory fall in bilirubin (0.08 to 0.50 mg/dL/h or 1.4 to 8.5 μmol/ L/h). Although it took some time for the world to realize the significance of this novel therapy, it is now the global standard of care(2-4).