Iowa Association of Municipal Utilities

FAQs of LED Street Lighting Anne Kimber, IAMU

akimber@iamu.org, 515.289.1999 ext 213

Terminology • Lumen: total amount of visible light emitted by a

source (lm) • Efficacy: the ratio of power emitted as light to the total

input power to the luminaire (lm/Watt) • Footcandle: lumens per square foot (lm/ft2) • Illuminance: lumens of light arriving at a unit of road

surface (footcandles or lux) • Luminance: the brightness of a light source in a

particular direction, or as reflected from a road surface and seen by an observer (candela/m2)

• Correlated Color Temperature: the color of light produced by a light source, (degrees Kelvin).

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Frequently Asked Questions (many)

• How is LED lighting different from other street lighting technologies? – Better control of light distribution pattern and

improved uniformity: • High Pressure Sodium lamps are high intensity

discharge near-point sources… leading to hot spots of illumination

• LEDs are multiple point sources which can be directed in a particular distribution pattern to increase uniformity

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Will LED street lighting improve lighting quality? 2 Answers: Increased Uniformity Higher Correlated Color Temperature with LED (higher blue light content contributes to visibility)

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FAQs continued • “Will LED street lighting save energy?

– Greater efficacy (greater lumens of light output per watt of power input) of LEDs AND more uniform lighting distribution will save energy

– From case studies, LEDs reduced energy consumption from 29-63%.

– Caution: must evaluate existing system: over-lit areas? Auburn example

• “Do LED street lights last longer than HID lighting – Yes. In IAMU’s joint purchase the estimated life of the LEDs

is in excess of 20 years. – Caution: Need good warranty from manufacturer

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FAQs continued

• “How will LED street lights reduce our maintenance costs”? – The long life of LED luminaires will reduce re-lamping

costs – Caution: Must match LEDs with Long-life

photocontrols • “Will installing LED street lights reduce our overall

costs?” – YES, and maintenance savings can be significant.

Need to analyze energy and maintenance cost savings using IAMU simple spreadsheet tool or by using the MSSLC financial calculator

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FAQs continued

• “Has the public liked the change from the yellow-orange of HPS to the white-blue of LED?” – IAMU case studies: YES- great public reaction, or

people didn’t notice the change – Suggest installing a test fixture and asking for

community feedback (Algona did this) – Web resources on MSSLC Gateway demonstration

projects such as Kansas City

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FAQs continued • “Are there health benefits or concerns with LED street

lights?” – Current research topic on overall effects of night time lighting

on human health. – 2010 DOE “Light at Night” white paper “given the available

research, it is unclear what changes, if any, should be made to current best-practice lighting design”

• “Do LED street lights reduce light pollution?” – Directional nature of LED lighting means that luminaire design

can lessen sky glow, – But shorter wavelengths are more easily scattered – The International Dark Sky Association Model Lighting

Ordinance provides guidance to reduce light pollution

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FAQs continued

• “What about street lights shining in people’s windows. Will LED street lights solve this problem?” – Design of LED optics can eliminate this problem – Select LED distribution pattern carefully

• “Are there best practice design guides for street lighting?” – RP-8 (2005) – AASHTO GL-6 (2005)

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FAQs continued

• “How do we know if a luminaire’s light distribution pattern is appropriate?” – There are 7 major distribution patterns, in IAMU’s

joint purchase we referred to light distribution pattern III (3).

– For LEDs, photometric calculations needed to ensure adequate lighting

– Suggest using RP-8 as local standard

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Luminaire Light Distribution Patterns

Figure 2 from the handbook. Modified with permission from Lighting for Exterior Environments (RP-33-99) published by the Illuminating Engineering Society of North America.

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Type II and III used in our roadway designs

FAQs continued

• “Are there any local, state or national regulations regarding street lighting?” – Local jurisdictions set regulations for street

lighting within a community. – Some communities have adopted RP-8 or AASHTO

GL-6 – International Dark Sky Association Model

Ordinance

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FAQs continued • “Should we hire a lighting professional to help

select luminaires and layout? – A lighting designer will be able to develop a

roadway lighting plan to take advantage of all the benefits LEDs offer

– Useful for roadway lighting in a new residential or commercial area

– Rapidly changing LED technology and wide range in performance can be challenging without professional assistance

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FAQs continued

• “Can we install the LED luminaires on existing poles and arms?” – Yes, but….pole height and spacing may not be

optimal so try to match the new illuminance level to existing illuminance.

– Most LED luminaires are designed to replace existing HPS on existing poles

– Need to specify the mounting configuration needed for the existing arm

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FAQs continued

• “Does it make sense to replace decorative luminaires with LED?“ – The handbook focuses on cobrahead and barn

light retrofit – Greater complexity in specifying retrofit LED

decorative luminaires – Sacramento study indicates costs greater than

benefits – Expecting rapid technology changes to bring

better solutions

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FAQs continued

• “How do we know if we’re getting a good product?” – Request for Bid process is recommended – MSSLC model specification tool

• “Are there standard LED replacement luminaires for existing luminaires?” – In a word, “no”. Significant variation. – Kansas City, Portland and Pittsburgh test cases

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FAQs continued • “Should we use an LED lamp that screws into the

existing HPS luminaire?” – LED optics are very different from HPS. – Use a high quality luminaire specifically designed for LED

to optimize light distribution • “Are there replacement parts? What happens when the

light “burns out” – LED chips more likely to dim – The “L70” factor refers to the number of hours at which

the LEDS have dimmed to 70 percent of its original light output.

– More likely that the driver or photo control will fail first

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FAQs continued (last of these!)

• “Should we use standard photocells…” – To save maintenance costs, use long-life

photocells

• “Are there more advanced ways to control LED luminaires?” – LEDs are instant-on and can be effectively dimmed – Dimming saves energy and extends the life of the

LED

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Federal and State Standards

• New efficacy standards – Iowa: 66 lumens/Watt – Minnesota: 70 lumens/Watt

• No USA-wide list in 2012 of state standards like Iowa and Minnesota

• In Iowa Statewide Urban Design and Specifications (SUDAS) refers to RP-8 but go beyond to include design criteria for LED roadway lighting, and include the Iowa efficacy standard

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Impact of LED on Roadway lighting design

• Discussion of lighting criteria for photopic (high light) versus mesopic (low light) conditions

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Figure 3 from handbook: photopic (black) and scotopic (green) luminosity functions

Light levels in mesopic conditions

• Lighting criteria currently designed for photopic (high light) conditions

• Mesopic conditions: the low light levels for which we provide streetlighting

• Design for mesopic conditions requires a new way of calculating the effectiveness of white light

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LED impact on roadway lighting design

• In dim light (mesopic conditions, our eyes are more sensitive to light that has more blue content.

• That means that new roadway lighting designs using LEDs may be able to reduce the design standard for required illuminance.

• San Jose Street Light Design Guide has method for calculating required illuminance with LEDs…..and the next revision of RP-8 is widely expected to include this topic.

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New Roadway Lighting Design • Provided by Mike Lambert- done with AGi32 software • Design for LED • Three simple designs:

– Residential Street – Typical Collector – Downtown Main Street with Intersection

• Based on RP8 illuminance (footcandle) criteria • Includes pavement classification (R3=typical asphalt

road with dark color and rough texture) • Pedestrian Vehicle Conflict Area • note the Illuminance ratios

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Table 1 Width 24 feetSpeed Limit 25 mphPedestrian-Vehicle Conflict LowPole Placement StaggeredDistance Between Poles 130 feetFixture Mounting Height 25 feetArm Length 4 ftPole Setback from Curb 3 ftPavement Classification R3Luminaire Wattage 53Lumens 3,913IESNA Light Distribution Type IIAverage Illuminance (fc) 0.4Avg/Min Illuminance Ratio 2.0

Residential Street CriteriaTwo lane local road

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Typical Residential Street

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Table 2 Width 52 feetSpeed Limit 30 to 45 mphPedestrian-Vehicle Conflict MediumPole Placement StaggeredDistance Between Poles 140 feetFixture Mounting Height 30 feetArm Length 6 ftPole Setback from Curb 5 ftPavement Classification R3Luminaire Wattage 210 WLumens 15,986IESNA Light Distribution Type IIIAverage Illuminance (fc) 0.92Avg/Min Illuminance Ratio 1.84

Collector Street CriteriaFour lane state or county road through town

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Collector roadway

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Table 3 Width 66 feetSpeed Limit 25 MPHPedestrian-Vehicle Conflict HighPole Placement OppositeDistance Between Poles 70 feetFixture Mounting Height 16 feetArm Length (Intersection) 8 ftPole Setback from Curb 6ftPavement Classification R3Luminaire Watts: Intersection 210 WLumens 15,986Luminaire Watts: Roadway 86 WLumens 4,630IESNA Light Distribution Type IIIAverage Illuminance (fc) 0.9Avg/Min Illuminance Ratio 4.0

Main Street CriteriaPole top luminaires and intersections

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Figure 8 Main Street

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Iowa Association of Municipal Utilities

Case Studies • Methods:

– Interviews- utility rationale, public process, feedback, installation experiences

– Cost data – IAMU analysis of payback, kWh saving, O&M saving – Illuminance (fc) measurements: Waverly, Algona

• Examples of diversity: – Small (Auburn) to large (Muscatine) – Cobrahead (8) to decorative LED lighting (1) – Joint purchase (eg Algona) versus single project

(Pocahontas) – Early adopter (Waverly)

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Case Studies key findings • Auburn

– Not interested initially, joined project after RFP process and competitive costs, changed 400 W to 150 W

• Independence – Bid process challenge because of Iowa statute changes

• Montezuma: opportunity for joint purchase was key driver in the installation

• Mount Pleasant: decorative lighting for economic development and downtown aesthetics

• Muscatine: grant funding reduced risk for a project they’d wanted to do

• Pocahontas: huge press for small and successful project • Spencer: early adopter and example for other communities • Waverly: like Independence, doing this in the middle of

efficacy statute rule changes, measuring street characteristics

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Estimated Annual Energy Savings and savings as a percent of pre-retrofit use

Case Study Community

Total Number of Retrofits

Estimated Annual Energy Savings from LED Retrofits

(kWh)

Energy Savings as Percentage of Original Energy Usage Pre-

RetrofitAlgona 447 234,254 46%Auburn 24 37,864 78%Independence 204 99,154 45%Montezuma 41 21,460 41%Mount Pleasant 130 70,378 57%Muscatine 301 155,534 51%Pocahontas 255 105,639 43%Spencer 153 57,632 29%Waverly 1010 403,805 63%Totals 2565 1,185,720 50%

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