Abstract: A reflected radiance sensor is held in a spaced-apart relationship with a surface so the field of view of the sensor intersects the surface so that the radiation reflected off the surface can be detected and measured. The sensor is configured to detect only reflected radiation so that the reflected radiation is accurately measured without any direct incident component. A support structure is utilized to hold the detector of the sensor in place. The support structure is preferably made of material that is substantially invisible (i.e., transparent) to the radiation wavelength band of interest. The design of a support structure in accordance with the present invention is not limited to any one design, but may be designed for optimum performance in a particular application.