From The Ground Up I: Light Pollution Sources in Flagstaff, Arizona

Abstract

We develop an estimate of the complete outdoor lighting of Flagstaff Arizona, as well as lighting-use densities (lumens per acre) for a number of different land uses. We find a total outdoor light output of 173 million lumens (Mlm) including sports lighting, and 139 Mlm without sports lighting, with an uncertainty of about 7%. The average fraction escaping directly upward from light fixtures is estimated to be 8.3%. After correcting approximately for near-ground blocking described in the accompanying paper by Luginbuhl et al., total uplight is estimated at 17.9 Mlm or 12.2 Mlm with and without sports lighting, respectively. Of these 17.9 Mlm, 33% arise from sports lighting, when it is on; when sports lighting is off, commercial and industrial lighting account for 62% with the remainder dominated by residential (14%) and roadway lighting (12%). We show that the 1989 Flagstaff lighting code that limited total outdoor lighting on new construction has reduced the growth rate of lighting, resulting in a 17% growth in light escaping into the sky from 1989 to 2003, compared to a 43% increase expected if the 1989 code had not been enacted. If all legally nonconforming lighting installed before 1989 were to be brought into compliance with the code, we would expect sky glow in Flagstaff to actually decrease by 36% compared to that in 2003; if all lighting, including residential, could be converted to fully shielded fixtures, sky glow would decrease to about half the current value. The implications for the most effective ways to address sky glow through lighting codes are discussed.