An illumination system having a refractive optical element that compensates for dependence in irradiance of images of objects captured by a photosensor is provided. The refractive optical element may structure the light such that similar objects in the same spherical surface in the field of view of the camera have the same irradiance on the camera photosensor. The illumination system may have an image sensor, a light source, and a refractive optical element. The image sensor has a photosensor that captures images of objects in a field of view. The irradiance of images of objects having a given exitance that are captured by the photosensor may depend on angular displacement from an optical axis of the image sensor. The refractive optical structures light from the light source to illuminate the field of view to compensate for the dependence of irradiance on angular displacement from the optical axis.