2022-074 Street Light Criteria & SEDNA Lighting PlanNovember 18, 2022 Report No. 2022-074
INFORMAL STAFF REPORT
TO MAYOR AND CITY COUNCIL
SUBJECT:
Street Light Criteria and SEDNA Lighting Plan.
EXECUTIVE SUMMARY:
The current criteria for street light placement (all types) is 300 feet with cobra head styles primarily
used on major thoroughfares at 100% brightness and acorn styles used on residential streets with
60% brightness. DME recently worked with an external engineering firm to review the placement
and brightness of street lights and they recommended we consider using the American National
Standard Institute / Illuminating Engineering Society RP-8 Recommended Practice for Design and
Maintenance of Roadway and Parking Facility Lighting (ANSI-IES). Both the TxDOT Highway
Illumination Manual and the American Association of State Highway and Transportation Officials
(AASHTO) GL-7 manual, which govern street lighting for state highways, rely on ANSI-IES RP-
8 as a source document for lighting levels.
DISCUSSION:
The primary focus for the various street lighting improvements that DME has focused on over the
last few years has been public safety to improve roadway/walkway visibility for motorists and
pedestrians/cyclists alike. This was in response to at least four pedestrian accidents on minor and
major thoroughfares. These accidents occurred at: (1) Bell and Mingo Rd; (2) I-35 and Mayhill
Rd; (3) McKinney and Loop 288; and (4) Audra and Oak Tree.
Denton Municipal Electric (DME) and Capital Projects/ Engineering (Engineering) have been
working together to provide street lighting direction to developers and contractors throughout the
city. Based on the current criteria, DME has continued to instruct developers to place street lights
at cul-de-sacs, intersections, and every 300 feet.
RP-8 directs light levels for streets and intersections based on street size and pedestrian activity
levels. The impacts of street lighting on a driver’s vision have been thoroughly studied and are
presented in the manual. The recommendations are based on several competing considerations.
To properly implement the lighting levels requires complex calculations to determine placement
of the luminaries. In most cases this requires a modeling program.
While RP-8 is the industry standard, the residential street requirements would create unacceptable
brightness levels and require placements of street lights with a separation distance that is very close
together. However, RP-8 does state that vehicle headlights may be adequate lighting for streets
with speeds of 30 mph or less but caveats that poor lighting may still impact safety. To address
residential lighting concerns, DME commissioned Kimley-Horn Engineering to study what other
municipalities throughout the state of Texas use as a standard for lighting residential streets.
November 18, 2022 Report No. 2022-074
While many cities use RP-8 recommendations for major thoroughfares, only Corinth, Austin,
Pearland, and Round Rock of the 50+ cities studied claimed to use RP-8 for residential
developments. Most cities had a separation requirement (either minimum distance or maximum
distance or both) between lights. The following tables show the minimum and maximum
separations used for residential lighting by the various cities studied. Denton’s previous
requirement of 300 feet is also plotted for comparison.
250
300 300 300 300
400
450
500
600
0
100
200
300
400
500
600
700
Separation DistanceCity
Minimum Separation Distance by City
125
400
500
600 600 600 600
700 700
900 900
0
100
200
300
400
500
600
700
800
900
1000
LubbockFort WorthIrvingPearlandHoustonDeSotoCarrolltonLake WorthDentonRound RockSan AntonioGrapevineGainsvilleMansfieldMesquiteOdessaSeguinWeatherfordBurlesonFlower MoundFriscoKellerLewisvilleNorth Richland HillsPlanoSaginawTempleMidlandSan AngeloMcKinneyRichardsonSeparation DistanceCity
Max Separation Distance by City
November 18, 2022 Report No. 2022-074
Based on the two graphs above, the average minimum separation for residential streetlighting is
roughly 250 feet and the average maximum separation is roughly 500 feet. It should be noted that
while RP-8 spacing is dependent upon light fixture and street characteristics, the set spacing
standard is independent of fixture type, etc.
DME currently maintains and installs 2 types of LED luminaires and a handful of pole types for
installations throughout the city. All LED lamps can be dimmed.
Cobra head lighting will be used for all major and minor thoroughfares; but
they were also used in some older residential neighborhoods. They are
purchased in 3 sizes (85 watts, 160 watts, and 241watst LEDs) according to
the level of lighting needed. In the residential neighborhoods, 85 watts level
is used. Cobra heads are mounted on wood poles, white concrete poles, or
metal poles with break-away bases as required by TxDOT in some locations.
Cobra head lights are dark sky compliant and do not produce up-light and will
be used to light major and minor thoroughfares with higher speed limits greater than 30mph. RP-8
spacing for these fixtures is around 250 feet or more at full (100%) brightness.
Post-top lighting in Denton is used either for residential neighborhoods or
streets in the historic district. Only one size is purchased (69W) and they are
not International Dark-Sky Association approved. During the April 27, 2021,
City Council meeting, Sustainability and DME personnel provided Council an
update on the LED street lighting retrofit program (ID 21-772) by DME. It
was the Council’s direction at this meeting that DME’s current post top
fixtures remain as the city’s design standard. These luminaires are installed
on concrete aggregate poles in neighborhoods and decorative metal poles in the historic district.
While currently spaced at 300 feet or less and dimmed to 60%, RP-8 lighting levels would require
these fixtures to be spaced approximately 80 feet apart or less at 100% brightness.
Dimming is a useful tool in residential neighborhoods where the post-top luminaires cast light on
more than just the roadway with light spill over into homes being bothersome to some residents.
DME, as a normal practice, dims residential lighting to 60% but may be able to dim to 50% in
coordination with sustainability efforts during bird migration seasons. For major and minor
thoroughfares, the cobra head lights will not be dimmed outside of residential neighborhoods due
to safety concerns. Additionally, cobra heads in residential neighborhoods will be dimmed to 60%
but since they emit no up light, no change is needed during bird migration seasons.
After reviewing the current lighting practices, RP-8, and the study results on other Texas cities,
DME proposes the residential street lighting standard be made a distance-based requirement and
that the distance be no more than 250 feet between each light. This corresponds to the approximate
average minimum separation of what the studied cities are using and places the city on the
conservative side of the maximum allowable separation curve. All other streets and thoroughfares
would be designed to RP-8 lighting requirements.
November 18, 2022 Report No. 2022-074
The following table summarizes the spacing and dimming requirements of the luminaires used by
Denton under the current and proposed standards as well as under RP-8 standards with the existing
fixtures and poles. Note these values are for residential streetlighting.
Streetlight Type Current
Separation
(ft)
Current
Dimming
(%)
Dark Sky
Compliant
Current Practice
Cobra Head 300 100 Yes
Post Top 300 60 No
RP-8 Standard (Residential)
Cobra Head 250 100 Yes
Post Top 10 to 80 100 No
Proposed Residential
Cobra Head 250 60 Yes
Post Top 250 60* No
All other streets per RP-8
* Additional dimming may be authorized based on bird migration patterns down to 50% for post tops once full LED
conversion is complete. Lighting on minor and major thoroughfares will remain at 100% given cobra heads have zero
up-light.
DME is finalizing a Street Lighting Manual that will be used in conjunction with the Electric
Service Standards to provide guidance to developers in Denton. All the requirements for lighting
residential and other streets under the city’s jurisdiction will be contained therein.
Southeast Denton Street Lights
Southeast Denton is currently being improved by installing sidewalks, improving streets, and
adding streetlights. Most of the streetlights in the Southeast Denton area are cobra head type
mounted on wooden poles. Many of these poles are part of the electric distribution system. New
and revised light placements are identified by a consultant as part of a lighting study. It has been
the practice of DME and Capital Projects/Engineering to install similar fixtures to what is already
existing (i.e., cobra head lights mounted on wooden poles).
In considering the possibility of installing post top fixtures, the following challenges exist:
1. Post top street lights are fed underground and this area primarily feeds existing street lights
by overhead lines.
2. Undergrounding may require additional easements and boring across the frontage of
properties and under the roadway.
3. Post top street lights may pose distance limitations to meet applicable electrical standards
from distribution lines.
4. Undergrounding will also pose an additional cost to this project and either delay the street
project or require DME to come in after the roadway is complete to install necessary
underground facilities.
November 18, 2022 Report No. 2022-074
Denton Development Code Section 7.11.6 – Street Lighting
On Thursday, November 10, 2022, staff provided the City Council an update on the above section
of the Denton Development Code as it relates to the Forestar Eagle Creek Development. The
following was provided:
“Item 2. Streetlights not hooded flooring Denton hooded light code.
The streetlights pictured (post top with acorn style globe) are a standard offering for residential
streets and are consistent throughout the city. Originally, staff responded they were not aware of
the hooded streetlight ordinance. After follow-up from a council member and the resident, staff
confirmed that streetlights are regulated under the Denton Development Code (DDC) 7.11.6 Street
Lighting which states: “All street lighting shall be full cut-off and designed to direct lighting below
a 90-degree horizontal plane extending from the lowest point of the light source.” The streetlights
in the Eagle Creek Development do not meet this provision. This provision of the DDC has not
been enforced.”
CONCLUSION:
DME recommends that new residential street lighting in Denton be required at cul-de-sacs,
intersections, and, at a minimum, every 250 feet placement. The developer for new residential
developments will be required to provide DME a copy of their lighting study based on the criteria
established and placed in the Street Lighting Manual.
DME recommends all major and minor throughfares street lighting be designed per RP-8
standards.
Regarding Southeast Denton, DME recommends that street lighting remain in the current overhead
configuration and use cobra head style fixtures as contained in the area’s lighting study.
Regarding Section 7.11.6 of the DDC, DME will work with the Development Services Department
to potentially remove this section and incorporate any desired changes within the Street Lighting
Manual.
STAFF CONTACT:
Aaron Bennion
Distribution Engineer, DME
Aaron.Bennion@cityofdenton.com
(940) 349-7117
REQUESTOR:
Staff Initiated
STAFF TIME TO COMPLETE REPORT:
8 hours
November 18, 2022 Report No. 2022-074
PARTICIPATING DEPARTMENTS:
DME, Capital Projects/Engineering, CMO