The measurement parameters for radiant energy, power, and irradiance also state that collimating optics must be used, if appropriate, in order to account for diverging laser sources. The collimating optics must have an optical power of 5 diopters or less (20 cm or longer focal length), as necessary to maximize detection. Naturally collimated or expanded laser beams that have low divergence and maximum detectability without collimating optics must be measured so that all the energy collectable within the specified aperture stop is considered. Multiple beams or diffuse sources that lie within a solid angle of acceptance of 10-3 sr must be included in the measurement.