Dobbins JLUS IMP Public Draft Light Pollution Study | Page 125

Section 4.6 Curfews.
Figure: 10pm etc.
Type: non-technical
Applying curfews to decorative and area lighting that is not directly associated with security
arises from the general principle of energy conservation and the idea that the
business/advertising and safety value of lighting when businesses are not open or late at night is
reduced. This is a compromise where lighting is reduced when business or safety impacts are
minimal, even though all night hours are of equal importance to professional astronomy -
astronomy begins at sunset and ends at sunrise. The specific times chosen are suggestions
only, and must be decided on a jurisdiction by jurisdiction basis following business activity and
community goals.
Section 5. Outdoor Advertising Sign Lighting Standards.
Section 5.1.A Lighting for externally illuminated billboards.
Figure: 200 lumens/sf
Type: technical
This figure is based on recommendations of the IESNA (IESNA, 2000) as well as a survey of
510 billboard faces in the Tucson metropolitan area. In the Tucson survey, 83% of the
billboard faces used 200 lumens per square foot and less.
Section 5.2 Internally Illuminated Sign, Neon Sign, Multicolor Fixed-Copy LED Sign and
Single-Color LED Sign Lighting Standards.
Figure: “ not white …”
Type: technical
A study by Luginbuhl (2002) shows that the total light output of a typical light-background
internally illuminated sign is about 7x that of a colored background sign, and 30x that of an
opaque background sign. Further, as the light emitted from internally illuminated signs is
directed sideways with 50% going upward and into the sky, the impact of such signage on
dark skies is disproportionate to the amount of light used in such signs. In other words, even
though signs do not account for a large amount of the light emitted by a city, because this light
is unshielded its impact is much greater than would be indicated by its proportion of the total
light output. In Flagstaff, where new light-background signs have been prohibited since 1989,
a survey (Luginbuhl et al., 2009) estimated that the total amount of upward-directed light
output due to signs was only 1.3% of the Flagstaff total; if these signs had used light
backgrounds this proportion would have been about 4%, 1.5x as much uplight as produced
by all hotels in the city, and almost 30x as much as produced by all roadway lighting.
Appendix A:
White Paper – Communities Addressing Light Pollution that Affect Nighttime Military Training
Section 5.3.A Multicolor Changeable-Copy LED Sign Lighting Standards. Multicolor
changeable-copy LED signs.
Figure: 100 nits
Type: technical
Unlike previous technologies, digital LED billboards are designed to produce brightness levels
that are visible during the daytime; though they are adjusted to fainter levels at night, should
too large a fraction of this brightness be used at night serious consequences for driver visibility
and safety are possible. Further, like any sign, the light emitted by billboards is unshielded, and
thus has a disproportionate impact on dark skies. A review of the lighting professional literature
(Luginbuhl et al,. 2010) indicates that drivers should be subjected to brightness levels of no
greater than 10 to 40 times the brightness level to which their eyes are adapted for the critical
driving task. As roadway lighting and automobile headlights provide lighting levels of about one
nit, this implies signage directed at drivers should appear no brighter than about 40 nits.
Standard industry practice with previous technologies, based on a survey of over 70 billboards
in the Phoenix, Chicago, Los Angeles and San Francisco metropolitan areas, shows such
billboards are illuminated on average to less than 60 nits (Luginbuhl et al., 2010, with
additional data), and rarely exceeds 100 nits. As these billboards were not limited in brightness
by any regulation, it appears sensible from all perspectives to limit digital billboards to 100 nits.
Section 5.4 Curfews.
Figure: curfews
Type: non-technical
As for Section 4.7, applying curfews to sign lighting arises from the general principle of energy
conservation and the idea that the business/advertising value of signage when businesses are
not open or late at night is reduced. Specifically regarding signs, the issues for unshielded
lighting discussed above under Section 5.2 also apply. The specific times chosen are
suggestions only, and must be decided on a jurisdiction-by-jurisdiction basis following
community goals.
Section 6. Special Uses.
Section 6.1.D Illuminance
Figure: [Illuminance]
Type: technical
The illuminance requirements are based on the IESNA Recommended Practice RP-6-01
(IESNA, 2001). Allowing 10% over the recommended levels allows an engineering design
margin.
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