an apparatus and method for photodynamic therapy or photodynamic diagnosis using an illuminator comprising a plurality of light sources generally conforming to a contoured surface and irradiating the contoured surface with substantially uniform intensity visible light . the light sources may comprise generally u - shaped fluorescent tubes that are driven by electronic ballasts . the spacing of the u - shaped tubes is varied to increase the output at the edges of the illuminator to make the output more uniform . also , different portions of the tubes are cooled at different amounts , to improve uniformity . a light sensor monitors output from the u - shaped tubes to provide a signal for adjusting the output from the tubes .