Here - PMOD/WRC

principle achieve better accuracy, the large area
photodiode approach is very easy to align using the front
surface reflection of the diode and may offer a more
practical link from radiometry to thermometry.
Measurements were taken with sphere apertures from 10 to
20 mm, and aperture separations from 300 to 800 mm.
This tested both the radiance uniformity of the rear wall of
the sphere and that inter-reflections were sufficiently low.
All results agreed within ±0.04%. The sphere was also
scanned horizontally by the pyrometer, and also indicated
a uniformity of better than ±0.04% (limited by the
measurement noise of the pyrometer). As the aperture can
be easily changed to ensure that the diode and the
pyrometer both view the same area of the wall, the effect
of radiance non-uniformity is expected to be