Facility for spectral radiance calibration at low light level

The spectral radiance measurement at daytime level can be realized with high accuracy, while it's difficult when the spectral radiance is at nighttime level. We design a spectral radiance calibration facility which has the characteristics of completely unchanged spectrum over 3 orders of magnitude and approximately unchanged spectrum for about 6 orders of magnitude. It combines a spectral radiance light source, a precision aperture and a white diffuser together, make it easy to reproduce the spectral radiance at 380 nm from 4 x 10-9 W/(m2<middle dot>sr<middle dot>nm) to 4 x 10-3 W/(m2<middle dot>sr<middle dot>nm). The facility can be easily used to calibrate a spectroradiometer at nighttime level. When the spectral radiance from 380 nm to 780 nm is around 1 x 10-7W/(m2<middle dot>sr<middle dot>nm), the calibration uncertainty of the spectroradiometer is 0.87%similar to 1.0% (k= 1).