The trap detector can be used as a power, irradiance, or radiance meter. Installing an aperture of known area in front of the trap detector allows it to be used as an irradiance meter. The addition of radiance measuring optics then converts the detector to a radiance meter. The provided Gershun (McCluney, 1994; Parr, 2005) radiance baffle tube contains three apertures. One aperture limits the field of view (FOV) to 5º and the other two reject stray light. Assuming that the trap detector has been calibrated for power responsivity, the difference from an ideal radiance is -0.012% for a 5 mm aperture and -0.006% for a 3.568 mm aperture.