夜間戰鬥機
The S/L layouts had been based on a spacing of 3500 yards, but due to equipment shortages this had been extended to 6000 yards by September 1940. In November this was changed to clusters of three lights to improve illumination, but this meant that the clusters had to be spaced 10,400 yards apart. The cluster system was an attempt to improve the chances of picking up enemy bombers and keeping them illuminated for engagement by AA guns or [[Night fighter]]s. Eventually, one light in each cluster was to be equipped with searchlight control (SLC) radar and act as 'master light', but the radar equipment was still in short supply.