Future long-term night sky monitoring projects shall use multispectral imaging sensors when possible

Interest in investigation of the impact of light pollution on ecology leads to a surge of observations and measurements. This article presents the measurement of the night sky radiance in over a period of 4.5 years in the city of Bremen, Germany from two sites situated in suburban and rural areas. It was found that both sites show a decreasing trend in sky radiance. However, since no multispectral images were taken, the exact cause of the decrease cannot be determined. It is therefore recommended that future night sky measurements should be based on multispectral imaging, for example by commercial digital cameras.