(Revised June 4, 2008) As an alternative to comparing the percentage difference of night illumination levels while the building\'s exterior and site lights are on to the levels while the same lights are off (20% maximum difference), project teams may compare the actual measured footcandle differences to the maximum allowable differences prescribed by IESNA RP-33, according to the specific zone. See the zone requirements below. Under this alternative path for Option C, project teams are still required to measure the night illumination levels at eight points with a maximum spacing of 100 feet apart, and each difference in footcandle measurement must be less than or equal to the maximum allowable value specified below. LZ1 - Dark (Park and Rural Settings) Exterior and site lighting must produce an illuminance difference no greater than 0.01 horizontal and vertical footcandles at the perimeter of the property. LZ2 - Low (Residential Areas) Exterior and site lighting must produce an illuminance difference no greater than 0.10 horizontal and vertical footcandles at the perimeter of the property. LZ3 - Medium (Commercial/Industrial, High-Density Residential) Exterior and site lighting must produce an illuminance difference no greater than 0.20 horizontal and vertical footcandles at the perimeter of the property. LZ4 - High (Major City Centers, Entertainment Districts) Exterior and site lighting must produce an illuminance difference no greater than 0.60 horizontal and vertical footcandles at the perimeter of the property. NOTE: IESNA RP-33 is referenced in the design & construction LEED rating systems; please note that LEED for Existing Buildings projects are not required to take night illumination level measurements beyond the site boundary. Applicable Internationally.