The work described was undertaken to develop a means to estimate the delivered power over the exposed body surface of a neonate receiving phototherapy. Previous work of the group had involved the use of discrete photodiodes distributed over a newborn manikin surface. It was considered that improved accuracy of sensing over curved surfaces would be provided with the use of flexible solar cell elements. A group of products based on amorphous silicon was identified as potentially suitable and a range of its properties investigated. These included the wavelength sensitivity, the relative sensitivity of similar elements and the cosine response of elements. It was identified that with selection of elements of matched sensitivity, specific element types were appropriate for intended use. A total of 44 discrete solar cell elements of three separate sizes was used to cover the previously used manikin surface and a dedicated interface circuit was designed and constructed. A handheld calibrated spectroradiometer provided a means to relate incident irradiance values within specific wavelength bands to corresponding optical power over the manikin surface. Initial use of the system is described together with future potential developments in relation to clinical applications and testing standards for neonatal phototherapy devices.