application note

CLD-AP69 rev 0

Figure 1

Cree® XLamp® XM-L
High-Bay Reference Design

Figure 1: XM-L high-bay prototypes(left: no optic design, right: Carclo Bubble optic)

Table of Contents

Introduction

Introduction......................................................... 1

There is a large market opportunity for LED-based

Design approach/objectives................................... 2

high-bay luminaires. World-wide market estimates of

The 6-step methodology........................................ 3

low-bay and high-bay luminaires, both as replacements

1. Define lighting requirements.......................... 3

for existing fixtures and as initial installations in new

2. Define design goals....................................... 8

construction, are in the hundreds of millions of units.

3. Estimate efficiencies ..................................... 8

High-bay luminaires incorporating the Cree XLamp XM-L

4. Calculate the number of LEDs .......................13

LED offer numerous benefits compared to traditional

5. Consider all design possibilities .....................15

high bay fixtures including energy efficiency, better

6. Complete the final steps...............................15

illumination and the ability to integrate with building

Conclusions........................................................22

control systems.

Special Thanks....................................................22
Until the release of Cree’s XLamp XM-L LED, several
hundred LEDs were needed to match the luminous
output of traditional high-bay lighting. The highly
efficient XM-L LED makes using this LED in a high-bay
luminaire a viable alternative to a metal-halide lamp.

www. cree.com/Xlamp

This application note demonstrates how to incorporate
the Cree XLamp XM-L LED into a high-bay luminaire.
An XM-L high-bay luminaire has multiple advantages
over traditional metal-halide lamps.

Copyright © 2011 Cree, Inc. All rights reserved. The information in this document is subject to change without notice. Cree, the Cree logo and
Copyright © 2010 Cree, Inc. All rights reserved. The information in this document is subject to change without notice.
XLamp are registered trademarks of Cree, Inc. This document is provided for informational purposes only and is not a warranty or a specificaCree, the Cree logo and XLamp are registered trademarks of Cree, Inc.
tion. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales atsales@cree.com. Other trademarks, product and company names are the property of their respective owners and do not imply specific productand/or vendor endorsement, sponsorship or association.

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

XLamp xm-l High-bay Reference Design•

No warm-up time•

No cool down needed before restart•No humming or flickering•

No mercury•

Longer lifetime•

No re-lamping cost, which can be a significant expense in high-bay applications•

No risk of lamp breaking, sending glass fragments over a large area•

Dimmable, enabling the use of occupancy sensors for power savings

Figure 2

Figure 2: Typical high bay installations

Cree created these XM-L high-bay prototypes with help from several driver and optical partners to show several different
approaches to an XM-L based high-bay luminaire design. These are only a few of the many possible implementations of
the XM-L LED into a high-bay design.

Design approach/objectives
In the “LED Luminaire Design Guide”1 Cree advocates a six step framework for creating LED luminaires and lamps. We
used this framework, with the design guide’s summary table reproduced below.
Step
1. Define lighting requirements

Explanation•

lighting requirements.
•

2. Define design goals

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

1	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 High-bay Reference Design

Step

Explanation

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 effiiciencies will drive the number ofLEDs needed in the luminaire.

4. Calculate the number of LEDs•

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

5. Consider all design possibilities andchoose 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 an easy-to-implement, high-efficiency XM-L LED-based luminaire capable ofreplacing the traditional metal-halide high-bay fixtures on the market. Cree framed the project as a fixture replacement,
so implementers can take full advantage of the XM-L LED’s superior performance.

1.

Define lighting requirements

Table 2 shows a ranked list of desirable characteristics for a high-bay luminaire.
ImportanceCriticalCharacteristics

Units

Illuminance distribution

Footcandles (fc)/lux

Electrical power

Watts (W)

Lifetime

Hours

Payback

MonthsLuminous flux

Lumens (lm)Manufacturability

ImportantOperating 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

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 3

XLamp xm-l High-bay Reference Design

Figure 3 below shows measured intensity data for metal-halide luminaires purchased from an industrial store, normalized
to show the light distribution for two types of luminaires.

Clear prismatic lensAluminum reflector

Figure 3: Goniometric intensity polar plot of metal-halide luminaires

Photometric testing and examination of existing high-intensity discharge (HID) metal-halide lamps provides comparison
data, shown in Table 3.

SourceLuminaire

Lamp

Power

Luminous Flux

(W)

(lm)

436

436

Fixture Total

FixtureUsableEfficacy

Lumens

Efficiency

Lumens*(lm/W)

29,01320,92454%

15,771

36.2

29,013

26,79061%

17,59740.4

HID aluminumreflector BT37
metal-halidelamp
HID clear prismatic lens BT37
metal-halide
lamp
Table 3: Metal halide comparison data

* Usable lumens define the light in the 0-60° zonal lumens distribution. The rest of the light is considered to be wasted.
The fixture efficiency, as defined in Cree’s “LED Luminaire Design Guide,”2 reflects the percentage of light that is useful.

2

Ibid., 6

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 High-bay Reference Design

Figure 5

Figure 4

Figure 4, Figure 5 and Figure 6 show the advantages of directional XLamp XM-L LEDs in this application. Omnidirectional
metal-halide lamps do not transmit all their light toward the target to be illuminated, resulting in losses within the
fixture. The directional XM-L LED transmits all its light toward the target, with minimal to no losses within the fixture. As
a result of this difference, a lumens-for-lumens match between an XM-L LED and a metal-halide lamp is only partiallyrelevant.

Figure 6

Figure 4: Typical metal-halide lamp
light distribution

Figure 5: Typical high-bay
luminaire light distribution

Figure 6: Typical high power LED light
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.

5

XLamp xm-l High-bay Reference Design

The Illuminating Engineering Society of North America (IESNA) gives performance requirements3 for various situations.
Category

Fc

Lux

A

3

32.3

Description

ExamplePublic space

Wine cellar

B

5

53.8

Simple orientation

Toilets & washroom

C

10

107.6

Working space simple tasks

Auditorium, locker room

D

30

322.9

Visual tasks of high contrast and large size

Library, museum

Visual task of high contrast and small or low contrast

E

50

538.2

F

100

1076.4Visual task of low contrast and small size

Basketball courtG

300

3229.2Visual task near threshold

Autopsy table, surgical task

and large size

Commercial kitchen, classroom

Table 4: IESNA requirements

The ENERGY STAR program provides general performance requirements.4 There are currently no specific ENERGY STAR
requirements for high-bay fixtures, however the following requirements apply to directional, commercial and indoor
luminaires.
Characteristic

Requirement
The luminaire must have one of the following nominal CCTs and fall within the corresponding 7-step chromaticity quadrangles as defined in ANSI/NEMA/ANSLG C78.3772008.

CCT

2700 K
3000 K
3500 K
4000 K
5000 K

Color angular uniformity
Color Maintenance

The variation of chromaticity shall be within 0.004 from the weighted average point on
the CIE 1976 (u’, v’) diagram.
The change of chromaticity over the first 6,000 hours of luminaire operation shall bewithin 0.007 on the CIE 1976 (u’, v’) diagram.

CRI

Luminaire shall meet or exceed Ra > 80.

Off-state power

Luminaires shall not draw power in the off state.
The luminaire and its components shall provide continuous dimming from 100% to 35%

Dimmingof 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.

Source start time

Light source shall remain continuously illuminated within one second of application ofelectrical power.

3
IESNA Lighting Handbook, 9th Edition
4
ENERGY STAR Program Requirements Product Specification for Luminaires (Light Fixtures) - Eligibility Criteria - Version 1.0
http://www.energystar.gov/ia/partners/prod_development/new_specs/downloads/luminaires/
ES_Luminaires_V1_Final_Specification.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.

6

XLamp xm-l High-bay Reference Design

Characteristic
Source run-up time

Requirement
Light source shall reach 90% of stabilized lumen output within one minute of applicationof electrical power.
Total luminaire input power ≤ 5 W: PF ≥ 0.5

Power Factor (PF)Total luminaire input power > 5 W:
PF ≥ 0.7 for residential
PF ≥ 0.9 for commercial

Warranty
Driver case temperature
Minimum operating temperature

3-year warranty for luminaires with replaceable drivers.
5-year warranty for luminaires with non-replaceable drivers.
Measured temperature for the hottest location on the driver case shall not exceed thedriver manufacturer’s maximum recommended temperature during in situ operation.
-18°C or below≥ 120 HzOperatingNote: This performance characteristic addresses problems with visible flicker due tofrequency

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

Luminaire efficacy
Minimum light output
Zonal lumen density
Lumen maintenance requirement

42 lm/W≤ 4.5 in. aperture: 345 lumens> 4.5 in. aperture: 575 lumens
Minimum of 75% of total initial lumens within 0-60° zone (axially symmetric about thenadir)
L70 ≥ 35,000 hours for commercial luminaires
Table 5: ENERGY STAR requirements

The DesignLights Consortium provides requirements for a high-bay luminaire.5
Application
Characteristic

High-Bay and Low-Bay Fixtures forHigh-Bay-Aisle Lighting

Commercial and Industrial Buildings
Minimum light output
Zonal lumen density
Nominal requirement, zone
Minimum luminaire efficacy

5> 10,000 lm≥ 30% 20–50°
60 lm/W> 10,000 lm≥ 50%, 20–50°≥ 30%, 0–20°
60 lm/W

Technical Requirements Table v1.5 http://www.designlights.org/solidstate.manufacturer.requirements.php

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 High-bay Reference Design

Application
High-Bay and Low-Bay Fixtures for

Characteristic

High-Bay-Aisle Lighting

Commercial and Industrial Buildings

Allowable CCTs

Minimum CRI
Minimum lumen maintenance requirement
at 6000 hrs
Minimum luminaire warranty

2700 K

2700 K

3000 K

3000 K

3500 K

3500 K

4000 K

4000 K

4500 K

4500 K

5000 K

5000 K

5700 K

5700 K

6000 K

6000 K

70

70

94.1%

94.1%

3 years

3 years

Table 6: DesignLights Consortium high-bay luminaire requirements

2.

Define design goals

The design goals for this project:
Characteristic

Unit

Illuminance profile

Fc

Power

W

Minimum Goal

Target Goal

same as 400 W

same as 400 W

metal halide lamp

metal halide lamp

< 250

200

Luminaire efficacy

lm/W

> 70

80

Lifetimehours

25,00050,000

K

7000

7000

identical

better

30

40

CCT
CRI
Maximum ambient temperature°C

Bill of materials (BOM) cost

$

400

400

Lumens (round output)lm

17,00017,000Lumens (oval output)lm

10,00010,0003.

Estimate efficiencies of the optical, thermal & electrical systems

Optical Efficiency
The two main optical losses in an LED system are light loss within the fixture and secondary optic loss. To eliminate light
loss within the fixture we designed the fixture so there is no light loss within it. This was done by spacing the LEDs far

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

Figure 7

XLamp xm-l High-bay Reference Design

enough from the edge of the fixture and close enough to the output so no light hits the sides and has to be reflected
out. Secondary optics can have light loss as high as 20% and as low as 7%.
To achieve as little secondary optic loss as possible, Carclo6 and Ledil7 optics were chosen having efficiencies as high as
93%.

Figure 8
The Carclo optic produces a round distribution of light wider than that of a high-bay
luminaire without an optic. Such a distribution is useful in illuminating a space such asa large retail store.

Figure 7: Carclo Bubble
optic

The Ledil optic produces an oval distribtion of light that is useful in illuminating spaces
such as aisles in a warehouse.

Figure 8: Ledil Strada
optic

Thermal Requirements
The XLamp XM-L LED operates at up to 10 watts of electrical power, depending on the drive current, and requires a heatsink to dissipate this thermal load. About 40% of that energy is converted to radiant flux and the rest to heat. Because
we want to the fixture to operate at less than 200 W, the heat sink will have to support a thermal load of 120 W.
The heat sink has two functions in this high-bay design: primarily to dissipate the thermal load of the LED, but also toprovide a frame for the fixture. This allows for as much surface area as possible to be exposed to ambient conditions
and takes full advantage of designing the luminaire around the XM-L LED. Cree chose to work with machined aluminum
to provide a series of large cooling fins. Machining of this prototype was done with the help of a local machine shop.
A STEP file for the heat sink and assembly mounting arm is available on the Cree website.8

6	Carclo Technical Plastics Ltd. website: http://www.carclo-optics.co.uk/
7	Ledil Oy website: http://www.ledil.com
8
http://www.cree.com/XLampModels/XLamp_ML_Highbay.zip

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 High-bay Reference Design

Figure 9

Figure 8: Machined aluminum heat sink

To verify the utility of this design, Cree performed thermal simulations using Ansys simulation software.9 Shown below
in Figure 9 is a simulation showing a cross section of the heat-sink housing with a 150-W thermal load at steady state
in a 25°C-ambient operating environment. The highest temperature in the simulation is at the solder point; the LED/heat-sink boundary never goes above 76°C, or 51°C above ambient. The thermal resistance of the XM-L LED is 2.5°C/W,
so the junction temperature will be ~89°C. With heat-sink thermal dissipation like this, the design will have no trouble
achieving a 50,000-hour L70 lifetime.10

9	Cree used Ansys Design Space, http://www.ansys.com/products/structural-mechanics/products.asp
10That is, after 50,000 hours of operation, in a well-designed system, the LED will still deliver at least 70% of its initial luminous
flux.

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

Figure 9

XLamp xm-l High-bay Reference Design

Figure 9: Ansys thermal simulation

Examining either the Cree Product Characterization Tool (PCT) or the relative flux vs. junction temperature graph in the
XM-L data sheet,11 an XM-L LED operating at a 89°C junction temperature will have a brightness of just less than 90%of the 85°C binning flux. Our measurements confirm this.

11

http://www.cree.com/products/pdf/XLampXM-L.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.

11

Figure 10XLamp xm-l High-bay Reference Design

Figure 10: XLamp XM-L data sheet: Relative luminous flux vs. junction temperature

Drive Electronics

Figure 11

While there are many excellent suppliers of LED control electronics and many ways to deliver controlled DC power tothe XLamp XM-L LED, Cree chose a readily available, full-range, off-the-shelf power supply from Thomas Research12
and Mean Well13 and a custom driver from NXP Semiconductors.14 We chose the Thomas Research driver because it isalready CE/UL certified, available from multiple distributors, has efficiencies as high as 91% and a power factor greaterthan 0.9. The NXP custom driver provides efficiency of ~95%, has four-channel output, a power factor above 0.9 andcan be configured to have occupancy sensing dimming.

Figure 11: Power supplies (left: Thomas Research, right: NXP)
12
Thomas Research model TRC-120S175ST http://www.thomasresearchproducts.com/led_drivers.htm
13	Mean Well USA Inc. website: http://www.meanwellusa.com
14
NXP Semiconductors website: http://www.nxp.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.

12

XLamp xm-l High-bay Reference Design

Table 8 below summarizes the calculated efficiencies of the optical, thermal and electrical systems for this high-bay
design.
SystemEfficiency

Type

Optical

93%

Light

Thermal

88%

Light

Electrical

92%

Power

Table 8: Optical, thermal, electrical efficiencies

4.

Calculate the number of LEDs

The design goal is to have a total of 17,000 lumens in a round beam and 10,000 lumens in an oval beam out of the
prototype fixture, so the actual lumens needed out of the LEDs after all the system efficiencies are take into account isshown below.
		Actual Lumens Needed = Target Lumens / (optical efficiency * thermal efficiency)
Round beam
Actual Lumens Needed = 17,000 / (93%*88%)
Actual Lumens Needed = 20,772 lm
Oval beam
Actual Lumens Needed = 10,000 / (93%*88%)
Actual Lumens Needed = 12,219
The XM-L LED delivers industry-leading flux and efficay. Based on the initial data, we chose to work with the Cool White,highlighted in yellow in Table 9 below, to give the closest possible CCT to a metal-halide lamp. These LEDs, running at
1.5 to 2 A, deliver less total flux than a 400-W metal-halide lamp, but the directionality of the XM-L LED source, with a125° beam spread, direct more flux toward the fixture opening than the spherical illuminance profile of the metal-halidelamp.
Group CodeMin. Luminous Flux
@ 700 mA (lm)Max. Luminous Flux
@ 700 mA (lm)

S6

182

200

T2

200

220

T3

220

240

T4

240

260

T5

260

280

T6

280

300

U2

300

320

Table 9: Order codes from XM-L binning and labeling document

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.

13

XLamp xm-l High-bay Reference Design

Figure 12
Basic XM-L LED electrical data and optical output from Cree’s Product Characterization Tool (PCT)15 is listed in Figure 12.

Figure 12: Cree’s Product Characterization Tool with XLamp XM-L flux data(left: with 92% optical efficiency and 90% driver efficiency, right: with no optical loss and 93% driver efficiency)

Depending on the drive current and the specific design goals to be achieved, the number of XM-L LEDs can vary greatly.
The PCT data in Figure 13 above shows this. After some experimentation and basic calculations with the use of the PCT,
we chose to drive 40 XLamp XM-L LEDs at 1.4 A for the no optic version. For the version with a wide-beam secondary
optic we chose to drive 32 XM-L LEDs at 1.7 A, but as few as 31 and as many as 76 LEDs can be used. Both versions
will be capable of meeting our 17,000 lumen output and less than 200 W power requirements. For the version with anoval-beam secondary optic, we chose to drive 24 XM-L LEDs at 1.4 A. This version will be capable of meeting our 10,000
lumen output and less than 200 W power requirements.
The purpose of this design exercise was to show that there are various ways to use XLamp XM-L LEDs achieve the light
output required of an LED based high-bay luminaire. The number of LEDs in the design depends on critical design goals
such as high efficiency and cost.

15

The analysis came from Cree’s Product Characterization Tool. 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.

14

Figure 13
XLamp xm-l High-bay Reference Design

Figure 13 shows a comparison photometric simulation using Dialux software. IES files for the high-bay simulation areavailable on the Cree website.16

Figure 13: Photometric simulation (left 32-LED XM-L high-bay prototype, right: metal-halide)5.

Consider all design possibilities

The main decision for the design of an XM-L LED based high-bay luminaire is whether to design a retrofit lamp or design
a fixture to replace a traditional bell-shaped fixture. Choosing to design a luminaire around the LEDs gives limitlesspossibilities. The luminaire can be lighter weight and smaller than a traditional fixture and can incorporate additional
functions such as dimming and occupancy sensing.
For this design Cree chose to do the following.
•

Maximize the coefficient of utilization.

•

Use off-the-shelf optics.

•

Design a heat sink that fits the design aesthetic and guarantees proper heat dissipation.

•

Use an off-the-shelf driver for the simplest solution and a custom driver for a more efficient solution.

•

Design a custom metal-core printed circuit board (MCPCB) that flexibly accommodates various numbers of LEDs
placed on it.

6.

Complete the final steps: implementation and analysis

This section illustrates the techniques Cree used to create a prototype high-bay luminaire using the Cree XLamp XM-L
LED and reviews the optical and electrical results.
16

http://www.cree.com/XLampModels/XLamp_ML_Highbay_IES.zip

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.

15

XLamp xm-l High-bay Reference Design

Prototyping Details
The essence of this prototyping design is to assemble the XM-L LEDs onto a MCPCB, mount this PCB onto a heat sink
and assemble these components with the necessary secondary optics and driver to create an LED-based luminaire
comparable to existing 400-W metal-halide high-bay fixtures. The prototyping steps are detailed below.

Figure 14

1.

MCPCB designa.

The initial design of the PCB used an MTS rapid prototyping milling machine. This allowed the design tobe adjusted before having the board made at a PCB company. Using the machine provided cost and time savings.

Figure 14: MTS rapid prototyping milling machineb.

Once the PCB design was proven, it was drawn and compiled to Gerber files by Copper Wave, Inc.17 andsent to Multilayer Prototypes, Inc.18 for PCB fabrication. The result is shown in Figure 16 below. The Gerber files
are available on the Cree website.19

17	Copper Wave, Inc. website: http://www.copperwavepcb.com/company.htm
18	Multilayer Prototypes, Inc. website: http://www.mpi-pcb.com/
19
http://www.cree.com/XLampModels/XLamp_ML_Highbay_MCPCB.zip

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.

16

Figure 15
XLamp xm-l High-bay Reference Design

Figure 15: XM-L prototype high-bay PCB

2.

Machining the heat-sink housinga.

Figure 16

To prove the design of the heat-sink housing, a prototype was machined from the drawing and files usedin the thermal simulations.
b.

The housing was machined and the mounting arm assembled by MCS Machine & Tool. The result isshown in Figure 16 below.

Figure 16: Machined housing

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.

17

XLamp xm-l High-bay Reference Design

3.

Assemble the drivers and PCB onto the housinga.

Figure 17

The XM-L LEDs were soldered onto the PCB following Cree’s Soldering and Handling Application Note for

the XM-L LED.20
b.

The optic was attached to the PCB.

c.

The power supply was mounted to the back of the housing.

d.

The PCB was attached to the housing using screws with thermal grease between the back of the PCB

and the housing.
e.

The PCB was connected to the power supply.

Figure 17: Assembled XM-L prototype high-bay luminaire

Results
Thermal Results
Thermal measurements were taken according to Cree’s Soldering and Handling Application Note for the XM-L LED.21
As Figure 18 shows, data collected from the XM-L LEDs in the prototype high-bay luminaire driven at 1.7 A demonstrate
thermal results and gradient in line with the thermal simulations.

20	Cree XLamp XM-L LED Soldering and Handling, Application Note AP54
http://www.cree.com/products/pdf/XLampXM_SolderingandHandling.pdf
21
Ibid.

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.

18

Figure 18
XLamp xm-l High-bay Reference Design

Figure 18: Thermal performance of 32-LED XLamp XM-L high-bay prototype driven at 1.7 A

Table 10 shows the solder point temperatures for the XM-L prototype high-bay luminaires.
Criteria

No Optic Result

Bubble Optic Result

Strada Optic Result

Tsp (°C)

65.8

71.6

62.5

Driver

NXPThomas Research

Meanwell

Optic

none

CarcloLedil# LEDs40

32

24

Table 10: Solder point temperature

Optical Results
Integrating sphere measurements22 show photometric and chromaticity data that exceed the design goals.
Criteria

No Optic Result

Bubble Optic Result

Strada Optic Result

Radiant flux (W)

60.85

58.61

31.67

Total luminous flux (lm)

17,11017,8009844

Power factor

.998

.994

.563

Efficacy (lm/W)

108

92.9

98.2

Optical efficiency (%)

n/a

92

92

CCT (K)

6851

7060

6898

CRI (Ra)

69.7

70.4

69.3

Chromaticity (x-coord.)

0.30760.30520.3127Chromaticity (y-coord.)

0.32220.31730.3266

Driver

NXPThomas Research

Meanwell

Optic

none

CarcloLedil# LEDs40

32

24

Table 11: Optical results
22	Measurements taken at Luminaire Testing Laboratory, Inc., website: http://www.luminairetesting.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.

19

XLamp xm-l High-bay Reference Design

Electrical testing23 shows the XM-L prototype high-bay luminaire achieves an efficacy that greatly exceeds that of thecomparison metal-halide fixtures.
Criteria

No Optic Result

Bubble Optic Result

Strada Optic Result

Power (W)

158

191.6

100.2

Power factor

.998

.994

.563

Efficacy (lm/W)

108

92.9

98.2

Driver

NXPThomas Research

Meanwell

Optic

none

CarcloLedil# LEDs40

Figure 19
32

24

Table 12: Electrical results

Goniometric measurements

24

show a consistent beam shape and light distribution for both XM-L prototype high-bay

luminaires.

No optic
Bubble optic

Figure 19: Goniometric intensity polar plot of XM-L prototype high-bay luminaire

The light intensity and distribution data25 in Table 13 and Table 14 show the XM-L prototype high-bay luminaire effectively
illuminates the area in which it is installed.

23
24
25

Ibid.
Ibid.
Ibid.

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.

20

XLamp xm-l High-bay Reference Design

Footcandles/Lux at Nadir

Diameter (ft/m)

Mounting

Aluminum

Clear

Aluminum

Clear

Height (ft/m)

Reflector

Prismativc

Reflector

Prismativc

6/1.8

167.1/1798.6

70.4/757.8

9.4/2.9

17.2/5.2

8/2.4

94.0/1011.8

39.6/426.3

12.5/3.81

22.9/7.0

10/3.060.2/648.0

25.4/273.4

15.7/4.8

28.7/8.7

12/3.741.8/450.0

17.6/189.4

18.8/5.7

34.4/11.4

14/4.330.7/330.45

12.9/138.9

21.9/6.7

40.1/12.2

16/4.923.5/253.0

9.9/106.6

25.17.7

45.8/14

Table 13: Metal halide light intensity and distribution

Footcandles/Lux at Nadir
Mounting

Diameter (ft/m)

No Optic

Bubble Optic

Strada Optic

No Optic

Bubble Optic

Strada Optic

4/1.12

323/3476.7

122/1313.2

62.9/677.0

5.5/1.7

12.7/3.9

11.9/3.6

6/1.8

143/1539.2

54.3/584.5

28.0/301.4

8.25/2.5

19.1/5.8

17.8/5.4

8/2.4

80.7/868.6

30.5/328.3

15.7/169.0

11/3.425.5/7.8

23.7/7.2

10/3.051.6/555.4

19.5/209.9

10.0/107.6

13.8/4.2

31.8/9.7

29.6/9.0

12/3.735.8/385.3

13.6/146.4

6.99/75.2

16.5/5.0

38.2/11.6

35.6/10.9

14/4.326.3/283.7

9.97/107.3

5.14/55.3

19.3/5.9

44.5/13.69

41.5/12.6

16/4.920.2/217.4

7.63/82.1

3.93/42.3

22/6.750.9/15.5

47.4/14.4

Height (ft/m)

Table 14: XM-L high bay light intensity and distribution

Cost of Ownership
The cost of the XM-L LEDs, heat sink and driver in this prototype high-bay design met the $400 BOM target. A single
HID metal-halide fixture typically retails for $180 – $250. Our BOM goal was not a primary factor for this design. Rather,high efficacy and effective light distribution were major considerations. This high-bay design is a prototype without any
manufacturing or component optimizations. Initial fixture cost aside, the following calculations show the savings an
XLamp XM-L LED high-bay luminaire can deliver.
For the cost of ownership calculations that follow:•

Assume that electricity costs $0.10 per kWh.

•The calculations don’t include the initial or replacement costs of the fixtures or the labor costs to replace a metalhalide lamp.

Table 15 compares the cost of ownership of the comparison HID metal-halide fixtures to that of the XM-L prototype
high-bay luminaires over the 50,000-hour lifetime of the XM-L LEDs. The metal-halide fixtures not only use significantly
more energy but also require three metal-halide lamps.
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.

21

XLamp xm-l High-bay Reference Design

Rated Lamp

Replacement-Lamp

Lifetime

Cost

436

20,000 hrs$11$2207.50

XM-L no optic

158

50,000 hrs-$790.00

XM-L Bubble optic

191.6

50,000 hrs-$958.00

XM-L Strada Optic

100.2

50,000 hrs-$501.00

High Bay Fixture
Metal halide

Lamp Wattage

Cost of Ownership

Table 15: Cost of ownership calculations

Table 16 shows the payback expected from the XM-L prototype high-bay luminaires as opposed to the comparison HID
metal halide fixtures after 3 years of use in several situations.
Payback Total
Usage
24 hours/day

XM-L

XM-L

XM-L

No Optic

Bubble Optic

Strada Optic$741.58$653.28$893.48

12 hours/day$376.29$332.14$452.24

8 hours/day$243.53$214.09$294.16

Table 16: Payback after 3 years

Conclusions
This high-bay reference design demonstrates the integration of the Cree XLamp XM-L LED into a high-bay luminaire to
replace a traditional high-bay fixture with great results. The design utilized proper heat sinking, optical control where
needed, and multiple driver options to efficiently and effectively hit the design targets and outperform comparison
metal-halide fixtures. Cree designed the heat sink and chose a driver to achieve a minimum L70 50,000-hr designation.
This design shows the level of performance that can be achieved but should not be interpreted as the only way that agood high-bay luminaire can be designed.

Special ThanksCree would like to acknowledge and thank the following partner companies that collaborated in the successful prototypingof this luminaire.
•

Carclo Technical Plastics Ltd., a division of Carclo plc•

Copper Wave, Inc.

•

Ledil Oy•

Mean Well USA•

Multilayer Prototypes, Inc.

•NXP Semiconductors•

Thomas Research

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.

22