P-64: Ultra-Uniform Oblong Integrating Light Source

Abstract

Many small uniform sources are integrating spheres often with a 1 % nonuniformity. By placing a cylindrical element between the two hemispheres we were able to reduce the nonuniformity to approximately 0.1 %. This makes such a calibration source much less sensitive to detector measurement-field size at the exit port.

Calibration Requirements for Demanding Measurement Challenges

“…To calibrate that factor, we make L 1 ( J ) as large as possible and measure the luminance L 2 . Thus, g = L 1 ( J max )/ L 2 , and for this prototype apparatus we find that g = 1,060 with an uncertainty of 10 percent (coverage factor of two) for L 1 above 1 cd/m 2 (for lower light levels, the uncertainty in g increases because of various factors discussed below). It is possible to monitor the photodiode current with a good picoammeter and then predict L 2 based upon the photocurrent J .…”

“…This reduces any aiming sensitivity in L 1 measurements. 2 Light from the exit port of sphere #1 travels through the SLET and into sphere #2. Thus, there should be a linear relationship between L 2 and L 1 based upon a geometrical factor g. To calibrate that factor, we make L 1 (J ) as large as possible and measure the luminance L 2 .…”

“…Sphere #1 has an extension between the two sphere halves that greatly decreases the nonuniformity of the baffle in sphere #1 to approximately 0.1 percent. This reduces any aiming sensitivity in L 1 measurements 2 …”

“…It is possible to monitor the photodiode current with a good picoammeter and then predict L 2 based upon the photocurrent J . However, to reliably reach and control the light in the realm of the limits of human vision of L rods = 3 × 10 –6 cd/m 2 , we would need to make sphere #1 have a luminance of L 1 = 0.003 cd/m 2 3 . It is possible to reach L rods with this prototype apparatus by looking at the exit port of sphere #2 using dark‐adapted eyes and averted vision, but because of the increase in the uncertainty of our measurements at these levels, the L 2 accuracy may be compromised.…”

78‐1: Specular Reflection Measurements on Reflective E‐paper Using a Variable Aperture Source

“…Use of a 3D printer made possible experimentation with different internal shapes of the integrating sphere, to maximize both uniformity and relative exit port size. Figure 3 shows the resulting source, with a capsule-shaped integrating volume where two hemispheres are separated by a cylinder the length of the hemispheres' radius [12]. This cylindrical extension greatly reduces luminance non-uniformity of the back hemisphere as viewed at the exit port.…”