The infants were randomized by sealed and opaque envelopes to one of four phototherapy regimens. Either with distance from the phototherapy device to the mattress of 20, 29, 38 or 47 cm measured by a wood stick for each infant, corresponding to the distances to the infants of averagely 12, 21, 30 and 39 cm, respectively.

The infants were placed in a bassinet with the phototherapy device placed above them. All infants were exposed naked (apart from eye pads and diaper) to continuously phototherapy for 24 hours, interrupted only for feeding and nursing for 30 minutes every three hours. TsB was determined before phototherapy and after 24 hours of treatment. The phototherapy apparatus used was neoBLUE LED phototherapy device (Natus Medical Inc., San Carlos, CA, USA) emitting blue light with an emission peak at 460 nm and a bandwidth of 450-470 nm. The irradiance was measured by use of the neoBLUE LED phototherapy radiometer (Natus Medical Inc.) every 8th hour at the infants head, trunk and knees and the average was calculated. The radiometer measures spectral irradiance in the range 420-500 nm with maximum sensitivity in the spectrum 440-480 nm.

TsB was measured before and after 24 hours of phototherapy and irradiance every 8th hour. Main outcome was 24 hours decrease of TsB expressed in percent (∆ TsB0-24(%).