that our measurements were obtained under closed cell conditions in which there was no possibility of contamination by daylight entering at the blanket's edge. Our measurements also showed that of the 74% of light transmitted by our samples, approximately 46% was scattered light which, due to its angle of incidence with the infant's skin, would be less effective than that normally incident at 90 degrees. Our findings lead us to concur with Dr Stutchfield and colleagues that thermal blankets

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... significantly reduce the effective irradiance of a phototherapy source. Commercial phototherapy units vary widely in their outputs in the 420-480 nm range, and these outputs are generally suboptimal.' 2 Many of these older phototherapy units are still in use. We suggest the use of more modern light sources, which do reliably achieve the recommended minimum irradiance of 1 mW/cm2, together with the avoidance of bubble plastic and other heat shields, whenever bilirubin concentrations are approaching exchange transfusion levels in very low birthweight babies. Heat and evaporative losses can be reduced instead by humidification.3 References Stutchfield PR, Modi N, Weindling AM. Phototherapy and the use of heat shields in very low birthweight infants. Arch Dis