A vacuum compatible integrating sphere was built to operate inside a thermal vacuum chamber. This paper presents the design and test results for a 1.65 meter diameter vacuum compatible integrating sphere with a 1.0 meter diameter exit port and approximately 10kW of internal tungsten lamps. Liquid nitrogen is used as cooling medium to remove the heat generated by these lamps. There are no moving parts inside the vacuum chamber.The radiance is monitored with two filter-wheel detectors, one TE-cooled silicon and one TE-cooled germanium, as well as a TE-cooled silicon array spectrometer. All three detectors are located outside the thermal vacuum chamber and view the sphere radiance through fiber optic cables.The system was tested inside a thermal vacuum chamber at NASA Goddard Space Flight Center before commissioning in the 5.5 meter thermal vacuum chamber at Space Applications Centre in Ahmedabad, India. Results of tests of radiance uniformity, radiance levels, and radiance stability are presented. Comparisons of the filter radiometers with the array spectrometer are also presented.
Application-specific integrating sphere-based, integral veiling glare measurement systems are described. The sources use the integral method for measuring the veiling glare (VG) index of various lens-based imaging systems. The calibration source has provisions in the form of a collimating lens holder to simulate a situation where the black target and bright surround are at a sufficiently great distance to give measurements of VG index which are the same as that which would result if the distance where infinite. The design criteria for the integral VG test source are presented. Included is a summary of the end-user specifications in regards to spectral radiance, levels of attenuation, irradiance stability, and aperture uniformity and contrast. Spectral radiometric predictions and actual output levels are compared Veiling Glare (VG) is completely defined in ISO-9358, but for expediency, it will be defined in this section with reference to Figure 1 for clarity. The illuminance of the focal plane is scanned while the lens system being evaluated views a uniform hemispherical radiance field created by an integrating sphere. The lens system also images a black spot (light trap with negligible reflectance) while scanning the focal plane field. The ratio of the illuminance at the focal plane of the lens while looking at the light trap to the illuminance of the sphere wall with no trap is the VG index. This ratio must also account for the ratio of the reflectance of the light trap to the reflectance of the sphere wall.AM1 is the spectral irradiance at the surface of the earth with the sun positioned directly overhead; i.e., light from the sun must travel through 1 air mass before reaching the ground. INTRODUCTIONThere are two systems described for measuring VG of a device under test (DUT). The two systems represent the extreme range of applications for the systems developed by Labsphere. The first system measures the VG for a groundbased, low light level night vision system which requires a CCT of 2856K and a luminance level in the range of 5 to 5E-5 foot-Lambert (fL). The second system required luminance levels above AM1 from 400-900 nm and provided radiance (no specification) from 250-1100 nm. In this case, AM1 was presented as spectral irradiance in units of W/m2-u.
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