Objective To measure the irradiance in humidified incubator under three different overhead phototherapy devices.

Design/methods The effective irradiance of three phototherapy devices was assessed by taking a series of irradiance measurements in the illuminated field. Measurements were made with a fixed bandwidth broadband radiometer (380–530 nm). The distance between the light source and the radiometer was 35 cm for the daylight fluorescent lamp, 40 cm for the light emitting diode (LED) and 50 cm for the halogen phototherapy. A double-wall incubator was kept at 36°C and set at three different levels of humidity (60–70%, 80% and equal or above 90%).

Results The irradiance under the overhead daylight fluorescent lamp phototherapy did not change with the increasing humidity. However, above 90% humidity, when water vapour inside the incubator was so saturated to the point of totally condensing in the incubator walls, the measured irradiance decreased 15% of the initial values with the blue LED phototherapy and 45% with the halogen spotlight phototherapy.

Conclusions Highly humidified incubators are frequently used to treat very low birthweight infants. Health professionals should be aware that mist and water condensation inside an incubator may significantly reduce the efficacy of treatment.