INTRODUCTION
This application note details the design of a high color rendering 70 watt equivalent retail track light using Cree XLamp CXA2540 LED integrated array.
The CXA2540 is optimized to simplify designs and lower system cost and can enable system-level performa nee of 4000 to 8000 lumens.
The XLamp CXA2540 LED integrated array delivers high lumen output and high efficacy in a single,easy-to-use package that eliminates the need for reflow soldering.
The XLamp CXA2530 LED integrated array highlighted in this reference design is optimized to enable applications that traditionally use halogen,
ceramic metaI haIide (CMH) and compact fluorescent lamp (CFL) technology. The goal of the design is to enable a retail track light with a narrow beam and excellent color rendering,
based on a single XLamp CXA2540 LED integrated array, delivering performance equivalent to a 70 watt CMH lamp.
IThis application note details the design of 39 watt CMH lamp.
TRACK LIGHT REFERENCE DESIGN
DESIGN APPROACH / OBJECTIVES
In the "LED Luminaire Design Guide" application note, Cree advocates a 6 step framework for creating LED luminaires.
All Cree reference designs use this framework, and the design guide's summary table is reproduced below.
Step Explanation
1. Define lighting requirements
2. Define design goa Is
3. Estimate efficiencies of the optical, thermal electrical systems
4. Calculate the number of LEDs needed
5. Consider a II design possibilities and choose the best
6. Complete final steps
The design goals can be based either on an existing fixture or on the application's lighting requirements.
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 env ironmental requirements.
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 lumina ire.
Based on the design goals and estimated losses, the designer can calculate the number of LEDs to meet the design goa Is.
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.
Complete circuit board layout.
Test design choices by building a prototype lumina ire.
Make sure the design achieves all the design goals.
Use the prototype to further refine the lumina ire design.
Record observations and ideas for improvement.
THE 6 STEP METHODOLOGY
The goal for this project is to demonstrate an easy-to-implement, high-output lamp that can better the light intensity of 70 watt CMH lamps currently on the market, showing that a narrow-beam,
high color rendering 70 watt equivalent retail track light is possible using a single XLamp CXA2540 LED integrated array.
1. DEFINE LIGHTING REQUIREMENTS
1 LED Luminaire Design Guide, Application Note APlS, www.cree.com/xlamp_app_notes/luminaire_design_guide
2 Production and cost-optimized implementations are beyond the scope of this document.
ENERGY STAR luminous efficacy, output and zonal lumen density requirements
Light source life requirements: all The LED package(s) I LED modules I LED a rray(s), including those incorporated into LED light engines or luminaires GU24 based integrated LED lamps, shall meet the following L70 lumen maintenance life values (refer to Lumen
Maintenance Requirements in the next section):
25000 hours for residential grade indoor luminaires
35000 hours for residential grade outdoor luminaires
35000 hours for commercial grade luminaires
Lumen maintenance life projection claims in excess of the above requirements shall be substantiated with a
TM-21 lumen maintenance life projection report.
Lumen maintenance The LED package(s) I module(s) I array(s), including those incorporated into LED light engines or GU24 based requirements: directional and integrated LED lamps, shall meet the following L70 (6k) rated lumen maintenance life values, in situ:
non-directional luminaires
L70 <25000 hours indoor residential
L70 <35000 hours mercia or outdoor residential
Compliance with the above shall be documented with a TM-211umen maintenance life projection report as detailed in TM-21, section 7. The report shall be generated using data from the LM-80 test report for the employed LED package/module/array model ("device"),
the forward drive current applied to each dev ice, and the in situ TMP 0 temperature of the hottest LED in the lumina ire. In addition to LM-80 reporting requirements, the following information sha II be reported:
sampling method and sample size (per LM-80 section 4.3) test results for each T5 and drive current combination description of device including model number and whether dev ice is an LED package, module or array (see Definitions)
ANSItarget, and calculated CCT value(s) for each device in sample set
chromaticity shift value on the CIE 1976 diagram for each dev ice in sample set
a detailed rationale, with supporting data, for application of results to other dev ices (e.g. LED packages with other CCTs)
Access to the TMP 0 for the hottest LED may be accomplished via a minimally sized hole in the luminaire housing, tightly resealed with a suitable sealant if created for purposes of testing.
All thermocouple attachments and intrusions to luminaire housing shall be photographed.
CCT requirements: all indoor The luminaire (directional luminaires), or replaceable LED light engine or GU24 based integrated LED lamp (nonВluminaires directional luminaires) shall have one of the following nominal CCTs:
2700 Kelvin
3000 Kelvin
3500 Kelvin
4000 Kelvin
5000 Kelvin (commercial only)
The luminaire, LED light engine or GU24 based integrated LED lamp shall also fall within the corresponding
7-step chromaticity quadrangles as defined in ANSI / NEMA / ANSLG C78.377-2008.
3 ENERGY STAR Program Requirements, Product Specification for Luminaires (Light Fixtures), Eligibility Criteria, Version 1.2, www.energystar.gov/ia/pa rtners/product_specs/progra m_reqs/Finai_Lumina ires_V1_2 .pdf?7b7d-2473
Color rendering requirements: all The lumina ire (directional luminaires),or replaceable LED light engine or GU24 based integrated LED lamp
indoor luminaires directional luminaires)shall meet or exceed Ra 80.
Color angular uniformity Throughout the zonal lumen density angles detailed Color maintenance requirements: The change of chromaticity over the first6000 hours of luminaire operation shall be within 0.007 on the CIE
solid state indoor luminaires only 1976 (u',v') diagram, as demonstrated by either:
the IES LM-80 test report for the employed LED package / array / module model, or
as demonstrated by comparison of lumina ire chromaticity data in LM-79 reports at zero and 6000 hours, or
as demonstrated by a comparison of LED light engine or GU24 based integrated LED lamp chromaticity data in
LM-82 reports at zero and 6000 hours.
Source start time requirement: Light source shall remain continuously illuminated within one second of application of electrical power. directional and non-directional
luminaires
Dimming requirements The lumina ire and its components shall provide uous dimming from 100% to 35% of total light output.
Step dimming, if employed, shall provide at least two discrete light output levels 35% of total light output and not including 100% output.
Power factor requirements: Totalluminaire input power less than or equal to 5 watts: PF 0.5 directional and non-directional
luminaires Totalluminaire input power greater than 5 watts: Residential: PF 0.7
Commercial: PF 0.9
Transient protection Ballast or driver shall comply with ANSI / IEEE C62.41.1-2002 and ANSI / IEEE C62.41.2-2002, Class A operation. requirements: all luminaires The line transient shall consist of seven strikes of a 100kHz ring wave, 2.5 kV level, for both common mode and
differential mode.
Operating frequency Frequency 120 Hz requirements: directional and
non-directional luminaires Note: This performance characteristic addresses problems with v isible flicker due to low frequency operation and
applies to steady-state as well as dimmed operation. Dimming operation shall meet the requirement at all light output levels.
Noise requirements: directional All ballasts, drivers, used within the lumina ire shall have a Class A sound rating and non-directional luminaires
Ballasts and drivers are recommended to be installed in the luminaire in such a way that in operation, the lumina ire will not emit sound exceeding a measured level
Table 4: ENERGY STAR luminaire requirements
The Designlights ConsortiumВ® (DLC) provides requirements for track or mono-point directional luminaires, summarized in Table 5.4
Minimum light output lm 250
Zona I lumen density 85%: 0-90 В; Minimum luminaire efficacy lm/W 45
Allowable CCTs (ANSIC78.377-2008) :5 5000
CRI 80
L70 lumen maintenance hours 50000
Minimum lumina ire warranty years 5
4 Designlights Consortium Product Qualification Criteria,Technical Requirements Table, v2.1, www.designlights .org/reso urces/file/technica1-reqs-ta blev2-1-f-u-1-1-t-a -b-l-e9 -2 7-14-pdf
We benchmarked two 70W CMH PAR38 lamps, using data from the lamps data sheets.
Light output lm 4300
Light intensity- maximum beam candle power(MBCP) cd 16000
Beam angle FWHM degrees 2S Efficacy lm/W 61
CCT K 3000
CRI 100 point scale 88
Average rated life hours 12000
Table 6: Performance data for 70W MH lamps
2. DEFINE DESIGN GOALS
Table 7 shows the design goals for this project.
3400
18000
20
49
3200
7S
8SOO
Characteristic
Light output
Light intensity- CBCP Beam angle- FWHM
Zona I lumen density
Luminaire efficacy
CCT CRI
Zonal lumen density
Luminaire efficacy
ccr
CRI
LED power
Luminaire power lm/W
K
100-point scale
w
Table 7: CXA2540 retail track light design goals
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 6 Figure 1 shows basic electrical data and optical output from the PCT. We estimated 90% optical efficiency,90% driver efficiency and a case temperature (Tc) of 80 В°C.
5 When used with a ba Ilast, the efAcacies of these lamps would be expected to be lower than shown in the table.
6 PCT is available at: pct.cree.com
The PCT output shows that, at 1.8 A, a single XLamp CXA2540 LED integrated array produces the desired lumen output and efficacy.
Thermal Requirements
The heat sink in this design must not only dissipate the heat generated by the LED, but also provide the mechanical frame for the LED, optic, and base. We used a market-ready heat sink/housing assembly, shown in Figure 2.
The heat sink is made of anodized aluminum alloy, AA 6063,and is part of a kit that includes a front optic cover ring. The diameter of the heat sink/housing assembly is slightly smaller (4.25 in/108 mm) than that of a PAR30 lamp.
We performed thermal simulation to verify that this thermal design is sufficient. 8 Figure 3 shows thermal images of the lamp assembly. The simulated case temperature CTc) is 82 В°C, within the operating limits of the XLamp CXA2540 LED
Figure 3: CXA2540 retail track light thermal simulation
8 For additional information on thermal management,refer to the ThermalManagement of Cree XLamp LEDs Application Note,APOS, www.cree.com/xlamp_app_notes/thermal_management
XLAMP CXA2540 HIGH-CRI RETAIL TRACK LIGHT REFERENCE DESIGN
Drive Electronics
Cree selected a commercially available constant-current driver to supply power to the retail track light. The driver, shown in Figure 4,can be located either on the track or above the ceiling.
Secondary Optics
It is a challenge to create a narrow-beam optic for a relatively large light source such as the XLamp CXA2540 LED integrated array.
This design meets the challenge with a hybrid reflector that is about 88% optically efficient and produces a 20В° beam angle.10
The low-profile reflector, shown in Figure 5, uses total internal reflection (TIR) and a reflective coating to provide high candela-per-lumen ratio and tight beam control.
Figure 5:Top (left) and bottom (right) views of CXA2540 retail track light reflector
The CXA LED Design Guide provides basic information on the requirements to use Cree XLamp CXA LEOs successfully in luminaire designs.11
4. CALCULATE THE NUMBER OF LEDS NEEDED
The dual purpose of this reference design is to show that a single LED package can deliver equivalent lighting utility and superior performance compared to existing 70W CMH lamps
on the market and show that it is possible to produce a narrow-beam retail track light based on the XLamp CXA2540 LED integrated array.
The CXA2540 LED integrated array is a multi-chip LED package that can offer the required CBCP with new levels of LED-to-LED color consistency and efficiency.
The XLamp CXA2540 LED integrated array can quickly enable superior LED lighting designs.
9 Model HLN-80H,Mean Well,www.meanwell.oom.cn
10 Model LL01ED-ASAxxl06-P,Ledlink Optics,Inc.,www.ledlink-optics.oom
11 Cree Xlamp CXA LED Design Guide,Design Guide DG02,www.cree.com/xlamp_app_notes/cxa_design_guide
We selected a Warm White LED for this reference design, shown highlighted in yellow in Table 8. To demonstrate the performance available from the CXA2540 LED integrated array, we chose the brightest LED at the desired CCT and CRI.
5. CONSIDER ALL DESIGN POSSIBILITIES
The design possibilities for an LED-based track light are innumerable. There are many ways to design the necessary heat sink that can dissipate the heat and also many ways to drive the LED and design the reflector and optics.
Carefully selecting a driver and a reflector provided the performance necessary for a true 70 W CMH-equivalent retail track light.
There are a number of desirable performance-related benefits in this design, which are results of the Xlamp CXA2540
LED package. Because the CXA2540 LED integrated array uses EasyWhiteВ® technology, LED-to-LED color consistency can be held to within two or four MacAdam ellipses for any given CCT, depending on the order code.
The CXA2540 LED integrated array is binned at 85 В°C, so the CCT will be as faithful as possible to the system operating environment. These component features allow for new levels of specification accuracy.
However, the primary purpose of this reference design is to show how simple and straightforward it is to design a high-CRI track light with Cree's XLamp CXA2540 LED integrated array.
This application note is not intended to show the only way to do this, but instead demonstrate the ease of implementation with this set of engineering constraints. Certainly numerous other successful solutions are possible.
Track Iight manufacturers typically design a reflector for a particular beam angle and install the Iight source and reflector in multiple housings. This reference design supports such a process and in addition,
the performance range of the XLamp CXA2540 LED integrated array enables a wide variety of luminaires that all use a single LED component. The high coloring rendering of this track light is a benefit for demanding retail applications.
CCTs from 2700 K to 5000 K and system-level lumen output up to 7000 lm are possible, providing the flexibility to offer a variety of luminaires that use a single LED light source and reflector.
6. COMPLETE THE FINAL STEPS
This section describes the techniques used to create a working high-CRIretail track light using the XLamp CXA2540 LED
integrated array and shows the results of the design.
Prototyping Details
The essence of the design is to attach a Cree XLamp CXA2540 LED integrated array to a heat sink and assemble the necessary optics and driver around this to create a true 70-W CMH-equivalent LED luminaire. The assembly steps are detailed below.
1. We verified the component dimensions to ensure a correct fit.
2. We fed the driver output wires through the center hole in the base of the heat sink and,following the recommendations in Cree's Soldering and Handling Application Note for the CXA family of LEDs,13 soldered them onto the CXA2540
LED integrated array.
3. We attached the CXA2540 LED integrated array to the heat sink with a small amount of thermally conductive compound. 14 Thermally conductive epoxy can also be used.
4. We tested the connection by applying power to the LED and verified that the LED lit up.
5. We placed a plastic alignment ring 16 over the LED and positioned the ring so the LED was centered on the heat sink.
6. We secured the plastic alignment ring to the heat sink with screws.
7. We placed the reflector in the heat sink so the opening aligned with the LED.
8. We screwed the front optic cover ring to the heat sink to secure the reflector to the heat sink.
9. We attached the track adaptor bracket to the lamp assembly with decorative screws.
10. We connected the driver input wires to the track adaptor.
11. We performed final testing.
Thermal Results
We measured the thermal performance of the retail track light by attaching a thermocouple to the XLamp CXA2540
LED integrated array mounted to the heat sink. The Tc of the CXA2540 LED integrated array was 85 В°C, in line with the thermal simulation and within the LED's operating limits.
Estimated LED Lifetime
We used Cree's TM-21 Calculator tool to determine the calculated and reported lifetimes for the XLamp CXA2540 LED integrated array.
The duration of Cree's CXA2540 LM-80 data set is 6,048 hours at 1.731 A and 85 В°C. The TM-21 methodology limits the projection to six times the duration of the LM-80 data set.
Optics and Electrical Results
IAA3 obtained the results in Table 9 by testing the retaiI track I ight in a 1.5 meter sphere and a Type A goniometer after a
The performance meets or exceeds the project goals and accomplishes this using a single XLamp CXA2540 LED integrated array to produce a symmetric 21 beam with CBCP of nearly 24000 cd.
The high CRIof this retail track light shows retail merchandise and artwork to its best advantage.
Ught output - 4103 lm
Ught intensity CBCP - 2987 cd
Beam angle- FWI - 21 degrees
17 Testing was performed at Cree's Shenzhen Technology Center. An IES file for the retail track light is available on the Cree website: www.cree.comlxlamp_app_ notes/CXA2540_highCRitrack_ ies
Table 10 shows the center beam illuminance of the CXA2540 retail track light at various distances from the light source.
1.0 m 3.3 ft 2,221 fc 23,908 lx 0.4 m 1.3 ft 0.4 m 1.3 ft
2.0 m 6.6 ft 555 fc 5, 977 lx 0.7 m 2.3 ft 0.7 m 2.3 ft
3.0 m 9.8 ft 247 fc 2,656 lx 1.1 m 3.6 ft 1.1 m 3.6 ft
4.0 m 13.1 ft 139 fc 1,494 lx 1.5 m 4.9 ft 1.5 m 4.9 ft
5.0 m 16.4 ft 89 fc 956 lx 1.8 m 5.9 ft 1.8 m 5.9 ft
CONCLUSIONS
This reference design demonstrates the ease of integrating the Cree XLamp CXA2540 LED integrated array into a high-CRI retail track light with excellent results. Such a luminaire is useful in both retail and residential spot light applications where enhancing the appearance of merchandise or artwork is desirable. The performance of this retail track light makes it an attractive alternative to CMH-based luminaires and could form the basis for a broad product line of track lights based on the CXA2540 LED integrated array. This performance comes without the mercury, ultraviolet light, risk of catastrophic breakage and long start-up and restrike times of CMH lamps. The system-level power consumption of the CXA2540 retail track light is an improvement over that of 70W CMH lamps operated with a ballast. This document is meant to show that this level of performance is achievable with a single XLamp CXA2540 LED based component, and
is meant to suggest that the CXA2540 LED integrated array can be the basis of numerous successful track light designs.
All nghts reserved The 1nformat1on m th1s document 1s subject tn change w1thout notice CreeВ®, the Cree logo, XLampВ® and EasyWh1teВ® are registered trademarks of Cree, Inc For product spec1ficat1ons,please see the data sheets available at www cree com For warranty mformat1on, please contact Cree Sales 11
