Dobbins JLUS IMP Public Draft Light Pollution Study | Page 111

W hy a lighting curfew for signs?
A number of jurisdictions within Arizona have had sign lighting curfews for many years,
including: Cochise County, Coconino County, Cottonwood, Pima County, Sedona, Tucson,
and Yavapai County.
According to the astronomy community, signs cause a substantial amount of light pollution
(estimated 10 percent of the total). A curfew is only in effect for non-business hours. Any
jurisdiction can adjust or eliminate curfews.
Why a sign brightness of 100 nits?
Nit is the standard unit used to measure the brightness of a surface, such as of a sign. The
POLC includes a maximum brightness of 100 nits for digital (multi-color LED) billboards. This
is based on the typical maximum brightness seen in current technology (floodlit) billboards.
The standard in some Arizona jurisdictions is 300 nits, a limit supported by the sign industry.
Based on an unpublished survey of 565 floodlit billboards in the Phoenix, Tucson and Chicago
metro areas, 1) more than 90 percent of floodlighted billboards are below 100 nits, and 2)
floodlit billboards illuminated at 100 nits are easily readable.
Besides energy and light pollution issues, there is a safety concern. Brighter signs (at three
times existing levels) may have an increased negative impact on driver vision and safety.
Why is sign color addressed in the code?
To help reduce light pollution it is best to stay away from white or very light-colored
background signs as they pollute the most. White background signs produce twenty times as
much light pollution as an opaque-background sign, and about six times as much light pollution
as a strongly colored-background sign.
Is the pattern code a lighting design standard?
The POLC is not a lighting design standard, and does not require a property owner or
business to meet any particular illumination levels. All standards in the POLC are intended to
limit the off-site or obtrusive aspects of outdoor lighting, such as glare with associated
decreased visibility, excessive energy use, and sky glow.
How do the POLC and the International Energy Conservation Code (IECC) 2009 outdoor
lighting allowances compare?
Summary: Roughly, IECC Lighting Zone 1 (LZ1) and Lighting Zone 2 (LZ2) are similar to
POLC LZ2 and LZ3; IECC LZ3 and LZ4 allow substantially more light than the POLC.
Comparison of the amount of outdoor lighting allowed under POLC and IECC 2009 is
complex, as the standards are written differently. The POLC is a simple lumens per acre
standard, requiring only the site acreage to determine the allowance. IECC 2009 specifies
allowances for a variety of uses, the amount determined by the area or linear dimensions of
each use (such as parking lots, walkways, entryways, sales areas, sales canopies, façade
lighting, etc.). In the IECC 2009 calculations below, we have assumed lighting will be used
only for the parking area and building façade: in general these will be the principal lighting uses
on most sites.
Site information:
site area = 1 acre
parking lot area = 0.6 acre
building perimeter = 200 feet
building height = 12 feet
façade area (perimeter x height) = 2400 ft.² fixture luminous efficacy (lumens per watt) = 60
(minimum); 75 (typical)
POLC lighting allowances
LZ 1 50,000 lm
LZ 2 100,000 lm
LZ 3 150,000 lm
IECC 2009 lighting allowances
LZ 1 93,000 lm (min); 116,000 lm (typical)
LZ 2 144,000 lm (min); 181,000 lm (typical)
LZ 3 223,000 lm (min); 279,000 lm (typical)
LZ 4 311,000 lm (min); 388,000 lm (typical)
Will POLC lumen caps affect liability?

The lumen limits in POLC are 50,000, 100,000 and 150,000 lumens per acre. The lowest,
50,000, is the limit that has been in place in 2/3 of urban Flagstaff for over 20 years. There
have been no complaints or cases where public safety was held to have been compromised
by these levels, and as such there is no increase in liability or liability insurance costs. 
Appendix A:
White Paper – Communities Addressing Light Pollution that Affect Nighttime Military Training
Page A- 43