光害
Light pollution is the level of radiance (night lights) shining up into the night sky. The Campaign to Protect Rural England (CPRE) divides the level of night sky brightness into 9 bands with band 1 being the darkest i.e. with the lowest level of light pollution and band 9 the brightest and most polluted. Broom with an index of 1-2 nanoWatts (nW) is in band 4. The night sky brightens towards Biggleswade but is darker to the west.