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copyright © 2010 cree, Inc. all rights reserved. The information in this document is subject to change without notice. cree, the cree logo and XLamp are registered trademarks of cree, Inc.

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0BCree® XLamp® XT-E LED

Streetlight Reference Design

cree, Inc.4600 Silicon Drive

Durham, Nc 27703USa Tel: +1.919.313.5300

appLiCaTion noTE

copyright © 2013-2014 cree, Inc. all rights reserved. The information in this document is subject to change without notice. cree®, the cree logo, XLamp® and Sc3 Technology® are registered trademarks of cree, Inc. eNerGY STar® is a registered trademark of the U.S. environmental Protection Agency. Other trademarks, product, and company names are the property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact cree Sales at [email protected].

inTRoDuCTion

municipalities from Beijing, china, to Los angeles, california, to apecchio, Italy, have implemented projects to replace traditional streetlights with energy-saving LeD streetlights. Local governments, universities and utility companies world-wide are taking advantage of the energy savings and lower maintenance costs provided by LeD-based streetlights and walkway lights.

This application note details the design of a prototype streetlight using cree’s XLamp® XT-e LeD to produce a Type III intensity distribution. Built on the Sc³ Technology® next-generation LeD platform, the XLamp XT-e LeD brings high performance and quality of light to this outdoor application. Streetlights incorporating the XLamp XT-E LED offer numerous benefits compared to traditional fixtures including energy efficiency, better

Reliance on any of the information provided in this Application Note is at the user’s sole risk. Cree and its affiliates make no warranties or representations about, nor assume any liability with respect to, the information in this document or any LeD-based lamp or luminaire made in accordance with this reference design, including without limitation that the lamps or luminaires will not infringe the intellectual property rights of cree or a third party. Luminaire manufacturers who base product designs in whole or part on any cree application Note or reference Design are solely responsible for the compliance of their products with all applicable laws and industry requirements.

TabLE of ConTEnTS

Introduction ........................................................ 1Design approach/objectives .................................. 3The 6-step methodology ....................................... 3

1. Define lighting requirements ............................ 32. Define design goals ........................................ 73. Estimate efficiencies of the optical, thermal &

electrical systems .......................................... 84. calculate the number of LeDs ........................115. consider all design possibilities .......................116. Complete the final steps: implementation and

analysis .......................................................12conclusions .......................................................17Special thanks ...................................................18Bill of materials ..................................................18

http://www.cree.com/XLamp

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XLamp® XT-E LED STrEETLighT rEfErEncE DESign

Copyright © 2013-2014 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree®, the Cree logo, XLamp® and SC3 Technology® are registered trademarks of Cree, Inc. ENERGY STAR® is a registered trademark of the U.S. Environmental Protection Agency. Other trademarks, product, and company names are the property of their respective owners and do not imply specific product and/or vendor endorsement, sponsorship or association. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at [email protected].

illumination and longer lifetime. The highly efficient XT-E LED makes using this LED in a streetlight a viable alternative to an incumbent-technology streetlight.

an XT-e streetlight has multiple advantages over traditional high-pressure sodium (HpS) and metal halide (mH) lamps.

• Lower energy usage• No warm-up time• No humming or flickering• No mercury• Longer lifetime• Better color rendering• No re-lamping cost, which can be a significant expense in streetlight applications

figure 1: LED streetlight installations

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DESign appRoaCh/objECTivES

The cree “LeD Luminaire Design Guide” advocates a six-step framework for creating LeD luminaires and lamps. we used this framework, with the design guide’s summary table reproduced in Table 1.

Step Explanation

1. Define lighting requirements • The design goals can be based either on an existing fixture or on the application’s lighting requirements.

2. Define design goals• Specify design goals, which will be based on the application’s lighting requirements.• Specify any other goals that will influence the design, such as special optical or environmental

requirements.

3. Estimate efficiencies of the optical, thermal & electrical systems

• Design goals will place constraints on the optical, thermal and electrical systems.• Good estimations of efficiencies of each system can be made based on these constraints.• The combination of lighting goals and system efficiencies will drive the number of LEDs needed

in the luminaire.

4. calculate the number of LeDs needed • Based on the design goals and estimated losses, the designer can calculate the number of LeDs to meet the design goals.

5. consider all design possibilities and choose the best

• with any design, there are many ways to achieve the goals.• LED lighting is a new field; assumptions that work for conventional lighting sources may not

apply.

6. Complete final steps

• complete circuit board layout.• Test design choices by building a prototype luminaire.• make sure the design achieves all the design goals.• Use the prototype to further refine the luminaire design.• record observations and ideas for improvement.

Table 1: Cree 6-step framework

ThE 6-STEp mEThoDoLogy

The major goal for this project was to create a high-efficiency XLamp XT-E LED-based 120-watt streetlight capable of producing a Type III beam pattern. Luminous flux and light distribution patterns for commercially available high-intensity discharge (HID) streetlight systems vary greatly by supplier, luminaire model, and ballast type. The 120-watt design goal for this LeD luminaire is meant to approximate the photometric performance of a typical 250- to 400-watt HID system.

1. DEfinE LighTing REquiREmEnTS

Table 2 shows a ranked list of desirable characteristics for a streetlight.

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/LED_Luminaire_Design_Guide.pdf

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importance Characteristics units

critical

Illuminance distribution footcandles (fc)/lux (lx)

electrical power watts (w)

Lifetime hours

payback months

Luminous flux lumens (lm)

Efficacy lm/w

Important

operating temperatures °c

operating humidity % rH

correlated color temperature (ccT) K

color rendering index (crI) 100-point scale

ease of installation

Table 2: Ranked design criteria for a high-bay luminaire

Figure 2, Figure 3 and Figure 4 show the advantages of directional XLamp XT-e LeDs in this application. omnidirectional HpS and mH lamps do not transmit all their light toward the target area to be illuminated, resulting in losses within the fixture. The directional XT-E LED transmits all its light toward the target area, with minimal to no losses within the fixture. As a result of this difference, a lumens-for-lumens match between an XT-E LED and an HPS or MH lamp is only partially relevant.

Figu

re 4

figure 2: Typical metal halide light distribution figure 3: Light distribution of typical metal halide streetlight

Figure 6

figure 4: Typical high-power LED light distribution

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The Illuminating Engineering Society (IES) defines both an intensity distribution classification and a luminaire classification system (LCS) for outdoor luminaires. The intensity distributions range from Type I, a “narrow, symmetric illuminance pattern,” to Type vS, a “symmetrical, nearly square illuminance pattern.” The IES defines a Type III intensity distribution as a “wide, asymmetric illuminance pattern” with the “highest intensity between 25° and 35° from nadir,” as shown in Figure 5. This is a useful distribution for a streetlight that is to illuminate not only a roadway but also a pedestrian walkway beside the roadway.

figure 5: Type iii intensity distribution

The LcS divides a luminaire or lamp’s lumen distribution into three solid angles, with each angle divided into secondary solid angles. The amount of light in each secondary solid angle allows luminaires to be compared and evaluated for a particular situation.

Figure 6 shows these secondary solid angles.1

Backlight (B) components indicate light trespass onto adjacent sites, opposite the area intended to be illuminated. Uplight (U) components produce artificial sky glow. Glare (G), shown as forward (F) components in the figure, can impair vision. At a low level it is merely annoying but at a high level it prevents clear vision and is a large liability.

figure 6: LCS solid angles

The IeS and the International Dark-Sky association (IDa) have issued the model Lighting ordinance (mLo) to assist local governments in defining standards for outdoor lighting related to light trespass, sky glow, and glare.2 The mLo uses the backlight, uplight and glare (BUG) classification of outdoor lighting fixtures defined by the IES in The Lighting Handbook

1 Joint IDa - IeS model Lighting ordinance (mLo) with User Guide, June 15, 20112 Ibid.

KeyBvH Backlight very High UH Uplight High FvH Forward Light very HighBH Backlight High UL Uplight Low FH Forward Light HighBm Backlight medium Fm Forward Light mediumBL Backlight Low FL Forward Light Low

For more information on FSA approved luminaires please visit the IDA Web site www.darksky.org.

A Classification System for Lighting Zones

The BUG

System

© International Dark-Sky Association • 3225 N. First Avenue Tucson, Arizona 85719 USA • www.darksky.org

BUG stands for “Backlight”, “Uplight” and “Glare.” The acronym describes the types of stray light escaping from an outdoor lighting luminaire. “B” stands for backlight, or the light directed in back of

the mounting pole. “U” stands for uplight, or the light directed above the horizontal plane of the luminaire, and “G” stands for glare, or the amount of light emitted from the luminaire at angles known to cause glare.

It is expected that BUG values will be published by luminaire manufac-turers so lighting specifiers, designers or purchasers can tell at a glance how well a certain luminaire controls stray light or compares with other luminaires under consideration for an installation.

The BUG system was developed by the Illuminating Engineering Society (IES) to make comparing and evaluating outdoor luminaires fast, easy and more complete than older systems.

Work on the BUG system started in 2005 when the IES upgraded the roadway shielding classification system. The original system, which included the ratings full cutoff, cutoff, semi-cutoff and non cutoff, had been designed as a rating system solely for street lighting. However, increasing demand for control of glare and light trespass extended these terms to all types of outdoor lighting, and the IES realized that a more comprehensive system was needed.

The Lighting Research Center, acting as an IES contractor, developed a new classification concept that addresses light emitted from the luminaire in all directions, not just up into the sky. This system, released to the public as IES Technical Memorandum TM-15, technically replaced the old system. It divides the sphere around a luminaire into zones assigning values according to expected environmental impact. This rating system offers the most complete evaluation of the total light emitted from luminaires to date. A point to

volume 2: issue 1 : 2009 — International Dark-Sky Association

Specifier Bulletin for Dark Sky Applications

The BUG System—A New Way To Control Stray Light from Outdoor Luminaires

http://www.ies.org/PDF/MLO/MLO_FINAL_June2011.pdf

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Tenth edition and in IeS Tm-15-11.3 The MLO defines limits for the amount of light that should be applied to each of five lighting zones. The lighting zones are described in Table 3, excerpted from the mLo.4

Zone Recommended uses or areas Zoning Considerations

LZ-0

Lighting Zone 0 should be applied to areas in which permanent lighting is not expected and when used, is limited in the amount of lighting and the period of operation. LZ-0 typically includes undeveloped areas of open space, wilderness parks and preserves, areas near astronomical observatories, or any other area where the protection of a dark environment is critical. Special review should be required for any permanent lighting in this zone. Some rural communities may choose to adopt LZ-0 for residential areas

recommended default zone for wilderness areas, parks and preserves, and undeveloped rural areas.

Includes protected wildlife areas and corridors.

LZ-1

Lighting Zone 1 pertains to areas that desire low ambient lighting levels. These typically include single and two family residential communities, rural town centers, business parks, and other commercial or industrial/ storage areas typically with limited nighttime activity. may also include the developed areas in parks and other natural settings.

recommended default zone for rural and low density residential areas.

Includes residential single or two family; agricultural zone districts; rural residential zone districts; business parks; open space include preserves in developed areas.

LZ-2

Lighting Zone 2 pertains to areas with moderate ambient lighting levels. These typically include multifamily residential uses, institutional residential uses, schools, churches, hospitals, hotels/motels, commercial and/or businesses areas with evening activities embedded in predominately residential areas, neighborhood serving recreational and playing fields and/or mixed use development with a predominance of residential uses. can be used to accommodate a district of outdoor sales or industry in an area otherwise zoned LZ-1.

recommended default zone for light commercial business districts and high density or mixed use residential districts.

Includes neighborhood business districts; churches, schools and neighborhood recreation facilities; and light industrial zoning with modest nighttime uses or lighting requirements.

LZ-3

Lighting Zone 3 pertains to areas with moderately high lighting levels. These typically include commercial corridors, high intensity suburban commercial areas, town centers, mixed use areas, industrial uses and shipping and rail yards with high night time activity, high use recreational and playing fields, regional shopping malls, car dealerships, gas stations, and other nighttime active exterior retail areas.

recommended default zone for large cities’ business district.

Includes business zone districts; commercial mixed use; and heavy industrial and/or manufacturing zone districts.

LZ-4

Lighting zone 4 pertains to areas of very high ambient lighting levels. LZ-4 should only be used for special cases and is not appropriate for most cities. LZ-4 may be used for extremely unusual installations such as high density entertainment districts, and heavy industrial uses.

Not a default zone.

Includes high intensity business or industrial zone districts.

Table 3: MLO-defined lighting zones

The maximum lumen levels for each BUG component are shown in Table 4, Table 5 and Table 6.5

Secondary Solid angle b0 b1 b2 b3 b4 b5

Backlight/Trespass

BH 110 500 1,000 2,500 5,000 > 5,000

Bm 220 1,000 2,500 5,000 8,500 > 8,500

BL 110 500 1,000 2,500 5,000 > 5,000

Table 4: Backlight ratings (maximum zone lumens)

Secondary Solid angle u0 u1 u2 u3 u4 u5

Uplight/Sky GlowUH 0 10 50 500 1,000 > 1,000

UL 0 10 50 500 1,000 > 1,000

Table 5: Uplight ratings (maximum zone lumens)

3 Luminaire Classification System for Outdoor Luminaires, IES TM-15-114 Joint IDa - IeS model Lighting ordinance (mLo) with User Guide, op. cit.5 Luminaire Classification System for Outdoor Luminaires, Addendum A. op. cit.

http://www.iesna.org/store/product/luminaire-classification-system-for-outdoor-luminaires-1103.cfm

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Secondary Solid angle g0 g1 g2 g3 g4 g5

Glare/offensive Light

FvH 10 100 225 500 750 > 750

BvH 10 100 225 500 750 > 750

FH 660 1,800 5,000 7,500 12,000 > 12,000

BH 110 500 1,000 2,500 5,000 > 5,000

Table 6: Glare ratings for Type III luminaire (maximum zone lumens)

The MLO defines two systems for evaluating outdoor lighting installations. One method prescribes a lumen limit for the site to be illuminated. The second method prescribes B, U and G values for each lighting zone for various installation parameters. This is to allow luminaires with different BUG ratings to be evaluated depending on the lighting zone of the area being illuminated. For example, whether a streetlight is mounted close to or far from the property line determines whether a higher or lower B rating is desirable.

There are currently no eNerGY STar® requirements for streetlights, however the DesignLights consortium® provides requirements for outdoor pole/arm-mounted luminaires, given in Table 7.6

Characteristicapplication

outdoor pole/arm-mounted area and Roadway Luminaires

outdoor pole/arm-mounted Decorative Luminaires

minimum light output 1,000 lm 1,000 lm

Zonal lumen density 100%: 0–90°,< 10%: 80–90° 65%: 0–90°

Minimum luminaire efficacy 70 lm/w 60 lm/w

allowable ccTs (aNSI c78.377-2008) ≤ 5700 K ≤ 5700 K

minimum crI 65 65

L70 lumen maintenance 50,000 hours 50,000 hours

minimum luminaire warranty 5 years 5 years

Table 7: DesignLights Consortium high-bay luminaire requirements

2. DEfinE DESign goaLS

The design goals for this project are given in Table 8. The luminaire efficacy goal was established to demonstrate the performance of the XLamp XT-E LED in this application. The power goal was established to reflect the tendency in the industry to offer 120-w LeD streetlights as replacements for 250- to 400-w HpS and mH streetlights. The lumen output goal is the product of these two goals.

6 Technical requirements Table v2.0

http://www.designlights.org/solidstate.manufacturer.requirements.php

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Characteristic unit minimum goal Target goalIlluminance distribution IeS Type III IeS Type III

power w 120 < 120

Luminaire efficacy lm/w 90 > 90

Light output lm 10,800 > 10,800

ccT K 5700 5700

crI 75 > 75

power factor 0.9 > 0.9

Table 8: Design goals

This reference design is not being developed for a specific lighting zone or installation location and we have not established a specific BUG rating design goal.

3. ESTimaTE EffiCiEnCiES of ThE opTiCaL, ThERmaL & ELECTRiCaL SySTEmS

we used cree’s product characterization Tool (pcT) tool to determine the drive current for the design. For the 10,800-lm target, we estimated 90% optical efficiency and 90% driver efficiency. We also estimated a solder-point temperature (TSp) of 50 °c.

The pcT output highlighted in Figure 7 shows the options considered for this reference design. For either the r3 or r4 flux code, 56-70 XT-E LEDs at 500-650 mA provide sufficient light output to meet the design goals. In an effort to use the minimum number of LeDs to meet the design goals, we used 56 XT-e LeDs operating at 650 ma.

figure 7: pCT output for number of LEDs and drive current

Design ConceptThis streetlight design uses an existing LeD streetlight housing and heat sinks. The XT-e streetlight is a modular design in which fourteen XLamp XT-e LeDs are mounted on a rectangular heat sink to form a module. The number of modules and the number of LeDs per module can be adjusted to achieve various light output levels. Secondary optics are used

1

LED System Comparison Report

System: 10,800 90% 90%

Model Model Model

Flux R3 [122] Tsp (ºC) 50 Flux R4 [130] Tsp (ºC) 50 Flux Tj (ºC) 25

Price -$ Price -$ Price -$

SYS lm tot SYS # LED SYS lm/W SYS W SYS lm tot SYS # LED SYS lm/W SYS W0.350 11554.6 98 103.7 111.475 12312.3 98 110.4 111.475 #N/A #N/A #N/A #N/A0.400 11099.5 84 100.6 110.342 11827.3 84 107.2 110.342 #N/A #N/A #N/A #N/A0.450 12250.9 84 97.7 125.351 10878.5 70 104.1 104.459 #N/A #N/A #N/A #N/A0.500 11133.3 70 95 117.134 11863.3 70 101.3 117.134 #N/A #N/A #N/A #N/A0.550 12023.7 70 92.5 129.961 12812.1 70 98.6 129.961 #N/A #N/A #N/A #N/A0.600 12881.7 70 90.1 142.93 10981.1 56 96 114.344 #N/A #N/A #N/A #N/A0.650 10966.9 56 87.9 124.824 11686 56 93.6 124.824 #N/A #N/A #N/A #N/A0.700 11602.1 56 85.7 135.392 12362.9 56 91.3 135.392 #N/A #N/A #N/A #N/A0.750 12217.3 56 83.6 146.063 13018.5 56 89.1 146.063 #N/A #N/A #N/A #N/A0.800 12808.1 56 81.7 156.811 13648 56 87 156.811 #N/A #N/A #N/A #N/A

Cu

rren

t (A

)

LED 1 LED 2 LED 3

Cree XLamp XT-E {AWT} x14 Cree XLamp XT-E {AWT} x14 (none)

Target Lumens : Optical Efficiency: Electrical Efficiency:

http://pct.cree.com

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to achieve the desired beam pattern. an o-ring between the secondary optics and the heat sink provides environmental protection. The driver is located inside the stainless steel streetlight housing, away from the heat sinks.

Thermal Requirementsproper thermal management is a key component of any successful LeD-based lamp or luminaire design. as with most LeD-based luminaire designs, this streetlight design requires a heat sink to dissipate the thermal load. The heat sink in this design, shown in Figure 8, is made of extruded aluminum, machined on one side with a flat surface for good thermal contact with a custom metal core printed circuit board (MCPCB). A groove near the edge of the flat surface permits the installation of a silicone o-ring. The o-ring provides environmental sealing and prevents the LeDs from coming in contact with contaminants.

figure 8: XT-E streetlight heat sink

This prototype streetlight design incorporates not only the heat sinks, but also the streetlight housing into the heat dissipation path. This helps to maximize the thermal transfer to the ambient environment. In addition, the streetlight housing has vents in both the top and bottom that allow airflow past the heat sinks. The heat sinks are located apart from each other in the housing to allow air to flow between them. Such vents would probably not be present in the top of a production streetlight. One alternative is to design the top of the housing to allow airflow while providing protection from debris.

cree performed thermal simulation to verify the thermal performance of this design. Figure 9 shows a thermal simulation of a cross section of a module at steady state in a 25 °c ambient operating environment. The simulated solder-point temperature was 46 °c.

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figure 9: XT-E streetlight module thermal simulation

Secondary opticsTo meet the Type III beam pattern requirement, we worked with LeDLink optics Inc. to develop a custom secondary optic for this design. Shown in Figure 10, the optic for each individual LED is 90% efficient. Fourteen individual optics were molded into an rectangular optic module that is attached to the heat sink. The optic module positions the optics in a 7 X 2 pattern and locates each optic above an LeD.

figure 10: 2 views of XT-E streetlight optic figure 11: XT-E streetlight optic module

Drive ElectronicsFor this streetlight design, cree chose a constant-current, universal-input-voltage driver, shown in Figure 12. The driver has an ingress protection (Ip) rating of Ip65. The driver is located within the streetlight housing away from the heat sinks.

http://www.ledlink-optics.com

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figure 12: XT-E streetlight driver

4. CaLCuLaTE ThE numbER of LEDS

The PCT output showed that 56 XLamp XT-E LEDs can provide sufficient light output to meet the design goals. We selected a Cool White LED for this reference design, shown highlighted in yellow in Table 9, to give the best efficacy while still meeting the DLc requirements. The directionality of the XT-e LeD source, with a 125° beam spread, directs more flux toward the fixture opening than the spherical illuminance profile of an HPS or MH lamp. By choosing an LED from a mid-level flux bin, we ensured that the design uses LEDs that are readily available.

XLamp XT-E LED Standard Kit Codes - White

Chromaticity

minimum Luminous

Flux (lm) @ 350 ma*

order Codes

Kit CCT Code flux (lm) no minimum CRi 70 CRi minimum 80 CRi minimum

aNSI cool white (5000 K – 8300 K)

51 6200 K

r5 139 XTeawT-00-0000-000000H51 XTeawT-00-0000-00000BH51

r4 130 XTeawT-00-0000-000000G51 XTeawT-00-0000-00000BG51 XTeawT-00-0000-00000HG51

r3 122 XTeawT-00-0000-000000F51 XTeawT-00-0000-00000BF51 XTeawT-00-0000-00000HF51

r2 114 XTeawT-00-0000-00000He51

53 6000 K




r2 114 XTeawT-00-0000-00000He53

50 6200 K




r2 114 XTeawT-00-0000-00000He50

Table 9: XT-E LED order codes

5. ConSiDER aLL DESign poSSibiLiTiES

as can be seen in the numerous LeD streetlight projects world-wide, there are an almost limitless number of ways to design an LeD-based streetlight. This reference design shows one way to design an excellent streetlight based on XLamp XT-e LeDs. contemporary, traditional and decorative streetlight designs are possible.

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6. CompLETE ThE finaL STEpS: impLEmEnTaTion anD anaLySiS

This section illustrates the techniques cree used to create a prototype streetlight using the cree XLamp XT-e LeD and reviews the optical and electrical results.

prototyping DetailsThe essence of this prototype design is to assemble four LeD modules, each with fourteen XLamp XT-e LeDs, and assemble the modules with the driver to create an LeD-based streetlight with a Type III beam pattern. The prototyping steps are detailed below.

1. We verified the component dimensions to ensure a correct fit.2. Following the XLamp XT LeD family recommendations,7 we reflow soldered fourteen XT-E LEDs onto each MCPCB,

connected in series, with an appropriate solder paste and reflow profile.3. We cleaned the flux residue with isopropyl alcohol.4. we applied a thin layer of thermal conductive compound to the back of the mcpcB and secured the mcpcB to the

heat sink with screws. consult cree’s chemical compatibility application Note for compounds safe for use with XLamp LeDs.

5. we fed the driver Dc output wires through the through-hole in each heat sink and soldered them to the terminal pads on the mcpcB. Figure 13 shows a module after this step. The four modules are connected in parallel.

figure 13: LEDs and mCpCb attached to heat sink

6. We tested the connections by applying power to the LEDs and verified they illuminated.7. Because of a streetlight’s outdoor operating environment, the LeDs could be exposed to substances that are harmful.

To prevent this, we installed a silicone o-ring in a groove in each heat sink. This prevents contaminants from entering between the LeD mcpcB and the optic module. as with the thermal conductive compound, the silicone o-ring is compatible for use with XLamp LeDs.

8. we positioned an optic module on each heat sink and secured it with screws, as shown in Figure 14.

7 cree XLamp XT LeD Family LeDs Soldering and Handling application Note

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLamp_Chemical_Comp.pdf

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLamp_XT_SH.pdf

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figure 14: LED module attached to heat sink

9. we attached the modules to the housing with screws.10. we attached the driver to the housing with screws.11. we closed the housing and secured it with the clips provided.12. We performed final testing.

ResultsThermal ResultsTo verify the thermal dissipation performance of the heat sink, we used a thermocouple to measure a steady-state solder-point temperature of 46 °c. This thermal performance exactly matches the thermal simulation.

Based on the measured solder-point temperature, the junction temperature (TJ) can be calculated as follows.

TJ = TSp + (LeD power * LeD thermal resistance)TJ = 46 °c + (1.95 w)/ * 5 °c/w)TJ = 56 °c

Estimated LED Lifetimewe used the environmental protection agency (epa) Tm-21 calculator to determine the calculated and reported lifetimes for the XLamp XT-e LeD at a 1-a input current and a 46 °c case temperature. The duration of cree’s XT-e Lm-80 data set is 6,048 hours at 55 °c, 85 °c and 105 °c. The Tm-21 methodology limits the projection to six times the duration of the Lm-80 data set.

with a reported L70(6k) lifetime greater than 36,000 hours and a calculated L70(6k) lifetime of 2,518,000 hours for the XT-e LeD, we expect the XT-e streetlight, with each LeD operating at 650 ma, to easily exceed an L70 lifetime of 50,000 hours.

Optical Resultswe obtained the results in Table 10 and following by testing the prototype streetlight at steady state after a 60-minute stabilization time.8 The streetlight provides the desired IES Type III illuminance distribution very efficiently. The wide

8 Testing was performed using a 1.5-meter integrating sphere and a Type a goniophotometer at cree’s Shanghai Technology center. An IES file for the streetlight is available.

http://www.energystar.gov/TM-21calculator

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XTE_streetlight_ies

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chromaticity range provided by the XLamp XT-e LeD enables differing local municipality requirements to be met by making the correct XT-e LeD binning selection.

Characteristic unit ResultIlluminance distribution IeS Type III

power w 119

Luminaire efficacy lm/w 97

Light output lm 11,541

ccT K 5700

crI 80

power factor 0.97

Table 10: XT-E streetlight steady-state results

The goniometric polar plot in Figure 15 shows a consistent beam shape and IeS Type III light distribution for the XT-e streetlight.

figure 15: Goniometric polar plot of XT-E streetlight (units - maximum candelas)

we used DIaLux software to simulate the illumination produced by the XT-e streetlight in a roadway installation.9 Figure 16 shows the mounting position of the streetlights in the simulation. The legend shows the various dimensions for the mounting position. The simulated distance between streetlights was thirty meters. Figure 17 shows the simulation roadway dimensions.

9 DIaLux 4.9, DIaL GmbH

http://www.dail.de

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Legend

(1) 10.0 m(2) 1.3 m(3) 0°(4) 1.5 m

0.00 30.00 m

0.00

21.00 m

figure 16: XT-E streetlight simulation mounting position figure 17: XT-E streetlight simulation roadway dimensions

Figure 18 shows the simulated illumination of a stretch of roadway illuminated by twelve XT-e streetlights, six on each side of the roadway, directly across from each other.

Legend

Color fc lx

0 0

0.35 3.75

0.70 7.5

1.05 11.25

1.39 15

1.74 18.75

2.09 22.5

2.44 26.25

2.79 30

figure 18: DiaLux simulation of XT-E streetlight

The american National Standard practice for roadway Lighting10 recommends several methods for evaluating roadway lighting. The illuminance method evaluates the amount of light reaching the roadway surface and makes recommendations based on the type and surface of the roadway and the amount of pedestrian traffic. Table 11 shows the illuminance method recommendations and XT-e streetlight results related to the illuminance method. The recommended values are for an expressway composed of dark asphalt paving having high pedestrian traffic. The uniformity ratio measures the evenness of the roadway illumination by comparing the average illumination value to the minimum value. The veiling

10 american National Standard practice for roadway Lighting, aNSI/IeSNa rp-8-2000

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luminance ratio indicates glare that inhibits drivers’ visibility. The recommendation for both ratios is a maximum allowed value.

minimum illuminance

uniformity RatioEavg/Emin

veiling Luminance Ratio

Lvmax/Lavgrp-8-2000 recommendation 14 lx 3.0 0.3

XT-e streetlight result 20 lx 1.7 0.1

Table 11: XT-E streetlight evaluation by illuminance method

The luminance method evaluates how “bright” a road is by determining the amount of light reflected from the pavement in the direction of a driver and makes recommendations based on the type and surface of the roadway and the amount of pedestrian traffic. Table 12 shows the luminance method recommendations and XT-E streetlight results related to the illuminance method. The recommended values are for an expressway composed of dark asphalt paving having high pedestrian traffic. The uniformity ratio measures the evenness of the roadway lamination by comparing the average lumination value to the minimum value. The recommendation for both ratios is a maximum allowed value.

minimum average

Luminance

uniformity RatioLavg/Lmin

veiling Luminance Ratio

Lvmax/Lavgrp-8-2000 recommendation 1.0 cd/m2 3.0 0.3

XT-e streetlight result 1.2 cd/m2 1.5 0.1

Table 12: XT-E streetlight evaluation by luminance method

The XT-e streetlight results, calculated as part of the DIaLux simulation, show that the XT-e streetlight betters the recommended values for both the illuminance and luminance methods.

The LcS graph in Figure 19 and the LcS values in Table 13 show how the XT-e streetlight achieves its B2-U3-G2 BUG rating.

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LCS Zone Lumens % LumensBL (0°-30°) 723.7 6.7

Bm (30°-60°) 1353.4 12.5

BH (60°-80°) 616.0 5.7

BvH (80°-90°) 39.0 0.4

UL (90°-100°) 58.7 0.5

UH (100°-180°) 110.7 1.0

FL (0°-30°) 1080.0 10.0

Fm (30°-60°) 4123.2 38.2

FH (60°-80°) 2445.5 22.7

FvH (80°-90°) 245.4 2.3

Table 13: XT-E streetlight LCS values

figure 19: XT-E streetlight LCS graph

The appropriateness of any streetlight in a particular installation depends on the streetlight position within the lighting zone of the application and the streetlight mounting height. as in any lighting application, a luminaire that is perfect in one installation can be less than satisfactory in another. we recognize that there are situations that require a streetlight to produce no sky glow, i.e., a BUG rating Uplight (U) value equal to zero. To achieve a U0 value with the prototype XT-e streetlight, the top of the housing could be modified to include shielding that prevents light from being emitted upward while maintaining the streetlight’s thermal performance.

ConCLuSionS

This reference design demonstrates integrating the cree XLamp XT-e LeD into a streetlight to replace traditional HpS and CH fixtures. Compared to 250- to 400-W HPS and MH streetlights, this prototype streetlight offers longer lifetime, and therefore lower maintenance costs, while using 50% to 70% less energy. Though a crI value as high as this streetlight’s value of 80 is not required in all situations, the XLamp XT-e LeD enables this when it is required or advantageous. This design shows the level of performance that can be achieved by combining the XLamp XT-e LeD with appropriate optics to produce a desired illuminance distribution. certainly optical control is important in a streetlight design and where light is not can be nearly as important as where light is, but a streetlight that does not sufficiently illuminate the site in which it is installed is of little use. This reference design shows that the XLamp XT-e LeD enables a streetlight that very usefully illuminates the roadway, walkway or parking lot in which it is located.

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SpECiaL ThanKS

cree would like to acknowledge and thank LedLink optics Inc. for their assistance in creating the secondary optics and optic module for this prototype streetlight.

biLL of maTERiaLS

Component order Code/model number Company Web Link

Driver HLG-120H-48a mean well USa, Inc. www.meanwellusa.com

LeD XTeawT-00-0000-00000HF53 cree, Inc. XT-e product page

optics LL14cr-aoc65150202 LedLink optics Inc. www.ledlink-optics.com

Thermal epoxy Silver Ice 710NS Timtronics www.timtronics.com/electricallyconductive.htm

Table 14: bill of materials for XT-E streetlight

Reliance on any of the information provided in this Application Note is at the user’s sole risk. Cree and its affiliates make no warranties or representations about, nor assume any liability with respect to, the information in this document or any LeD-based lamp or luminaire made in accordance with this reference design, including without limitation that the lamps or luminaires will not infringe the intellectual property rights of cree or a third party. Luminaire manufacturers who base product designs in whole or part on any cree application Note or reference Design are solely responsible for the compliance of their products with all applicable laws and industry requirements.

http://www.meanwellusa.com

http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Discrete-Directional/XLamp-XTE-White

http://www.ledlink-optics.com

http://www.timtronics.com/electricallyconductive.htm

Documents

XTE Streetlight Ref