Most likely these folks were replacing bulbs on a group replacement basis. Since many older street lighting circuits all come on/went off at the same time either from an automatic or manual central control, it always made sense to replace all the lamps within group circuits at the same time after x-number of operating hours (approaching lamp end-of-life). Most incandescent street lighting bulbs were designed for this sort of scheduled maintenance; typically for group replacement operations at around 80% of average lamp life (the latter usually was 3,000 or 6,000 hours). This method was quite economical since it was less expensive than sending a truck out for individual, spot replacements. In addition, glassware was cleaned and replaced if needed while lamps were being replaced in groups. Of course, bulbs that prematurely failed were promptly spot-replaced within group replacement cycles.

Overview photo. Three closer views of areas of interest within this photo follow.