Because of the integrating sphere’s ability to produce multiple diffuse internal reflections and a uniform illumination of the inner sphere wall, it is the right tool to form the basis for uniform light sources.
Uniform light sources are required to calibrate the uniformity of imaging systems and the luminance output of luminance meters, spot exposure meters and other photometric equipment.
The standard is constructed around the integrating sphere of various diameters which provide the highly uniform diffuse luminance at the exit port required for these types of calibrations. The spheres may be coated with BaSO4 or machined with our OP.DI.MA. difuse material. Seasoned tungsten halogen sources are typically used with lamp power supplies and temperature stabilized photometric reference detectors to form the complete system. Control feedback loop techniques control the luminance output intensity and help prolong the useable lifetime of the system. Any change in ambient and sphere body temperature affecting the output signal is eliminated through the temperature stabilized reference detector. This also reduces system warm-up time.
An optimally designed sphere layout is capable of less than ± 0.7% non-uniformity over 90% the port opening which can be as large as 100 mm in diameter (see example below). Angular uniformity of less than ± 5% within ±40° enables luminance output calibration of detection systems with wide acceptance angles. Luminance outputs can range from 0.5 to 35000 cd/m2. Some standards may offer a variable luminance (or spectral radiance) output requiring more sophisticated electronics, multiple lamps and exhaust fans.
Luminance output, uniformity and angular uniformity must be measured and certified in the Gigahertz-Optik calibration facility.
Additional information from our Products section: 