CLD-AP71 REV 0

APPLICATION NOTE

Cree® XLamp® XM-L EZW
MR16 Reference DesignFigure 1: MR16 assembly

Introduction.......................................................1
Design approach/objectives...............................2
The 6-step methodology.....................................3
1. Define lighting requirements......................... 3
2. Define Design goals..................................... 6
3. Estimate efficiencies.................................... 6
4. Calculate the number of LEDs ...................... 7
5. Consider all design possibilities .................... 8
6. Complete the final steps............................... 8Conclusions......................................................11INTRODUCTION
The design presented here builds on the “Cree XLamp
MT-G MR16 Reference Design”1 to describe a design for
a 20 W - 25 W MR16 replacement lamp. The XM-L EasyWhite LED has a smaller footprint than the MT-G andallows development of an MR16 replacement bulb forlower lumen density applications.
Though this application note focuses on the XM-L EZW
LED, Cree offers a family of EasyWhite (EZW) products

WWW. CREE.COM/XLAMP

that can be applied to MR16 and related applications.

1Cree XLamp MT-G MR16 Reference Design, Application Note AP62 http://www.cree.com/products/pdf/XLampMTG_MR16_Ref.pdf
Other trademarks, product and company names are the property of their respective owners and do not imply specific product and/or vendor
Copyright© 2010Cree, Inc.
rights reserved. The information in this document is subject to change without notice.
endorsement,sponsorshipor Allassociation.
Cree,the Cree
logoCree,and XLamp
registeredtrademarksof Cree, inInc.
Copyright© 2011
Inc. Allare
rightsreserved.
The information
this document is subject to change without notice. Cree, the Cree logoand XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or aspecification. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree
Sales at sales@cree.com.

Cree, Inc.
4600 Silicon Drive
Durham, NC 27703
USA Tel: +1.919.313.5300

XLAMP XM-L EZW MR16
REFERENCE DESIGNDESIGN APPROACH/OBJECTIVESIn the “LED Luminaire Design Guide”2 Cree advocates a six step framework for creating LED luminaires and lamps. We
use this framework, with the design guide’s summary table reproduced below.
Step
1.

Explanation

Define lighting requirements•

The design goals can be based either on an existing fixture or on the application’slighting 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 orenvironmental requirements.

3.

Estimate efficiencies of the optical,•Design goals will place constraints on the optical, thermal and electrical systems.

thermal & electrical systems•

Good estimations of efficiencies of each system can be made based on these constraints.

•The combination of lighting goals and system effiiciencies will drive the number ofLEDs needed in the luminaire.

4.

CalculatethenumberofLEDs•

needed5.

Based on the design goals and estimated losses, the designer can calculate thenumber of LEDs to meet the design goals.

Consider all design possibilities and•With any design, there are many ways to achieve the goals.

choose the best•

LED lighting is a new field; assumptions that work for conventional lighting sources
may not apply.

6.

2

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.

LED Luminaire Design Guide, Application Note AP15, www.cree.com/products/pdf/LED_Luminaire_Design_Guide.pdf

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

2

XLAMP XM-L EZW MR16
REFERENCE DESIGN

THE 6-STEP METHODOLOGY
The main goal of this project was to demonstrate the ease of developing a replacement for halogen MR16 bulbs currently
on the market, showing that an equivalent 20-W – 25-W MR16 bulb can be made available at a reasonable cost. Theproject was framed as a retrofit, so this project’s MR16 bulb can be used in installed track lighting and fixtures.

1.

DEFINE LIGHTING REQUIREMENTS

The table below lists important characteristics to consider for the design of the MR16 in this reference design.
ImportanceCriticalCharacteristics

Unitslight intensity

CBCP (foot-candles)

beam angle (FWHM)

degrees

electrical power

watts (W)luminous flux

lumens (lm)form factor

per ANSI C78.21.2003

bulb-to-bulb consistency

Importantprice$lifetime (L70)

hours

operating temperatures°C

operating humidity% RH

correlated color temperature (CCT)°K

color rendering index (CRI)

100-pt scale

driver power factor
manufacturablilty
Table 1: Target MR16 luminaire characteristics

Measurement of 20-W halogen MR16 lamps purchased from a home improvement store provides basic benchmark data.
SourceMeasured Power

Luminous Flux

Efficacy

CBCP (cd)Beam Angle

CCT(W)(Lm)(Lm/W)(°)(K)

MR16 A

20.78

280

13.5

420

362900

MR16 B

21.17

254

12.0455302780

MR16 C

20.66

260

12.6

950

222780

Table 2: Benchmark halogen MR16 dataMeasurement of these MR16 halogen lamps shows the inconsistency of the beam angles. The graphs in Figure 2 show
the measured data, normalized to show the light distribution for the comparison halogen lamps. The data show variationin the peak intensity locations and beam shape. This application note shows that an XM-L EZW based MR16 significantly
improves on these light distributions, creating a repeatable beam of the same intensity.

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

3

Figure 2

XLAMP XM-L EZW MR16
REFERENCE DESIGN

Figure 2: Measured goniometric intensity polar plot of halogen MR16

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

4

XLAMP XM-L EZW MR16
REFERENCE DESIGN

Data from the Energy Star Program Requirements for Integral LED Lamps gives us additional performance requirements.3
General Energy Star Luminaire Requirements:
Correlated Color Temperature (CCT)The luminaire must have one of the following designated CCTs and fall within the 7-stepchromaticity quadrangles as defined in the Appendix.

Nominal CCT

Target CCT (K) and tolerance

Target Duv and tolerance

2700 K2725 ± 145

0.000 ± 0.006

3000 K

3045 ± 175

0.000 ± 0.006

3500 K3465 ± 245

0.000 ± 0.006

4000 K

3985 ± 275

0.001 ± 0.006

Color Maintenance
Color Rendering Index (CRI)

The change of chromaticity over the minimum lumen maintenance test period (6000hours) shall be within 0.007 on the CIE 1976 (u’,v’) diagram.
Minimum CRI (Ra) of 80. In addition, the R9 value must be greater than 0.
Lamps may be dimmable or nondimmable. Product packaging must clearly indicate
whether the lamp is dimmable or not dimmable. Manufacturers qualifying dimmable

Dimming

products must maintain a Web page providing dimmer compatibility information.
Minimum efficacy, light output, CCT, CRI, and power factor of dimmable lamps will be
confirmed with the lamp operated at full power.

Warranty
Allowable Lamp Bases

A warranty must be provided for lamps, covering material repair or replacement for aminimum of three (3) years from the date of purchase.
Must be a lamp base listed by ANSI.
For lamp power ≤5 W and for low voltage lamps, no minimum power

Power Factor

Minimum Operating Temperaturefactor is required For lamp power >5 W, power factor must be ≥ 0.70
Note: Power factor must be measured at rated voltage.
Integral lamp shall have a minimum operating temperature of -20°C or below.
≥ 120 HzLED Operating

Note: This performance characteristic addresses problems with visible flicker due to low

Frequency

frequency operation and applies to steady-state as well as dimmed operation. Dimming
operation shall meet the requirement at all light output levels.

Electromagnetic and Radio Frequency In-Integral LED lamps must meet the appropriate FCC requirements for consumer use (FCCterference

47 CFR Part 15).

Audible Noise

Integral lamp shall have a Class A sound rating.
Power supply shall comply with IEEE C.62.41-1991, Class A operation. The line transient

Transient Protection

shall consist of seven strikes of a 100 kHz ring wave, 2.5 kV level, for both common
mode and differential mode.

Operating

Lamp shall operate at rated nominal voltage of 120, 240 or 277 VAC, or at 12 or 24Voltage

VAC or VDC.

3

http://www.energystar.gov/ia/partners/product_specs/program_reqs/ILL_prog_reqs.pdf

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

5

XLAMP XM-L EZW MR16
REFERENCE DESIGN

2.

DEFINE DESIGN GOALS

The design goals for this project:
Characteristic
Luminaire Light Output

Unit

Minimum Goal

Target Goal

Lm250

280

Same

Better<5<5Illuminance/Luminance ProfilePowerW

Beam Angle°3636

Center Beam Candle Power (CBCP)

Cd470

490

Hours

25,00050,000K

3,000

3,000Lifetime
CCT
CRI

80

Bulb-to-bulb consistency3.

< 4-step McAdams Ellipse

85< 2-step McAdams Ellipse

ESTIMATE EFFICIENCIES OF THE OPTICAL, THERMAL & ELECTRICAL SYSTEMS

Component Efficiency

Figure 3

For the the 6-V and 12-V version of XM-L EZW LED, figure 3 shows their basic LED electrical data and optical output from
Cree’s Product Characterization Tool.4

Figure 3: Cree’s Product Characterization Tool with XLamp XM-L EZW data4

http://pct.cree.com

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

6XLAMP XM-L EZW MR16
REFERENCE DESIGN

Thermal Requirements
An XLamp XM-L EZW LED operating at 5 or more watts of power, at steady state temperature, needs a heat sink todissipate the thermal load. In an LED-based MR16 design, the heat sink must not only dissipate the heat generated by
the LED, but also provide a mechanical frame for the LED, optic, driver and base and, to be an MR16 retrofit, fit into theANSI-standard enclosure defined in ANSI C78.24-2001. To demonstrate the ease of creating a high quality XM-L EZW
MR16 retrofit lamp, Cree chose an off-the-shelf heat sink from Neng Tyi Precision Industries Co., Ltd.5 for this design.

Drive Electronics
For this reference design, Cree did not attempt to be compatible with all 12V transformers, instead choosing a commonly available electronic transformer, the Lightech6 LET 60 LW, a low-wattage transformer compatible with both LED
and incandescent MR16s.
The design for the MR16 driver used a design from Diodes, Inc.7 based on their AL8806 controller. The driver efficiency
was calculated to be 81.1%.

Secondary Optics
The baseline CBCP intensity was determined from the Energy Star Integral LED Lamp Center Beam Intensity Benchmark
Tool (ed. 7/6/2010).
Cree’s collaboration with Carclo Technical Plastics Ltd., a division of Carclo plc,8 produced a 30-mm TIR lens compatible
with the XM-L EZW LED that fit in the heat sink and was greater than 93% efficient.

4.

CALCULATE THE NUMBER OF LEDSOne.
The purpose of this reference design was to show the ease of using a single XM-L EZW LED package to deliver equivalentillumination and better efficacy than halogen bulbs on the market. The XLamp XM-L EZW LED is a multi-chip LED package that can offer the CBCP required of an MR16 replacement bulb with improved LED-to-LED consistency and efficiency.

5678

Neng Tyi website: http://www.nengtyi.com.tw
Lightech Electronic Industries, Ltd. website: http://lightechinc.com
Diodes, Incorporated’s website: http://www.diodes.com/zetex/cree
Carlo website: http://www.carclo-optics.com

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

7

XLAMP XM-L EZW MR16
REFERENCE DESIGN

5.

CONSIDER ALL DESIGN POSSIBILITIESThere are innumerable ways to design a retrofit MR16 bulb. Using Cree’s MT-G MR16 reference design as a guide, Creeselected components that result in a 20 W - 25 W halogen MR16 replacement bulb, fulfilling the primary design goal—toshow the ease of designing such a bulb with Cree’s XLamp XM-L EZW LED.
The XM-L EZW LED brings a number of benefits to the design. Because of the XM-L LED’s EasyWhite technology, LEDto-LED color consistency is guaranteed to within two or four MacAdam ellipses (for a given CCT and depending on theorder codes). The XM-L EZW LED has a CRI minimum of 80, with higher CRI available, and is binned at 85° C, so theCCT will be as faithful as possible to the system environment. These features enable new levels of specification accuracy.

6.

COMPLETE THE FINAL STEPS: IMPLEMENTATION AND ANALYSIS

Prototyping Details

Figure 4

The assembly of the XM-L EZW LED with the heat sink, optics and driver followed the steps detailed in Cree’s MT-G reference design. The components are shown in Figure 4. The result is a 20 W - 25 W halogen MR16 replacement.

Figure 4: XM-L EZW MR16 components

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

8

XLAMP XM-L EZW MR16
REFERENCE DESIGN

Figure 5
Results
Thermal results:
Infrared images9 indicate that the maximum surface temperature of the lamp is 54 –55° C.

Figure 6
Figure 5: Thermal images

Figure 6 shows the measured solder point temperature (Tsp) and ambient temperature (Ta) over a 40-minute period.
Based on the measured solder point temperature, the operating wattage of the LED and the typical thermal resistanceof 2.5°C/W for the XML-EZW LED, the junction temperature (Tj) was calculated to be 76.8 °C.

Figure 6: Solder point and ambient temperature of XM-L EZW MR16

Optic Results:
The optic results for the XM-L EZW MR16 show a beam angle of 36° and an optic efficiency of 93.4%. The graph in
9Photographs were taken using a FLIR T300 at Cree’s facility in Durham, NC.

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

9

XLAMP XM-L EZW MR16
REFERENCE DESIGN

Figure 7Figure 7 shows the measured intensity data, normalized to show the light distribution for the XM-L EZW MR16 lamp. The
data show consistent beam shape and light distribution, with the same intensity as comparison halogen lamps.

Figure 7: Measured goniometric intensity polar plot of XLamp XM-L EZW MR16

The data in Table 3 demonstrate that a 20 W MR16 halogen replacement that meets Energy Start requirements is possible with a single XM-L EZW LED.
LED

LightPower

Efficacy

Beam

CBCP

Output(W)(lm/W)

Angle

(cd)

(lm)
6-V XM-L EZW

275

CCT

CRI

Tsp
(°C)

(°)
4.76

57.6

36620

2990

82

67.1

Table 3: System test data, steady stateThis design was able to achieve 20 W MR16 halogen equivalency based on the Energy Star requirements. The measured
CBCP was 620 cd, above the minimum 496 cd required for a 36° beam. The lumen output was 275 lumens at steadystate. Figure 8 shows the beam profile and intensity distribution.

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

10

XLAMP XM-L EZW MR16
REFERENCE DESIGN

Figure 8

Figure 8: Measured intensity distribution of 20 W equivalent XM-L EZW MR16

CONCLUSIONS
The goal of the design was to enable an LED-based MR16 replacement retrofit bulb that delivers performance equivalent
to 20-W – 25-W halogen MR16s and conforms to Energy Star requirements. This reference design demonstrates the easeof incorporating a Cree XLamp XM-L EZW LED into a conventional MR16 housing and meets the Energy Star requirements for a 20-W – 25W MR16 replacement. This document shows that this level of performance can be achieved witha single XM-L EZW LED but should not be interpreted as the only way that a good MR16 replacement can be designed.

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and XLamp are registered trademarksof Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specification. For product specifications, please see the data sheets available atwww.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.

11