Special thanks ................................................. 12
Bill of materials ................................................ 12
IntRoDuCtIon
This application note details the design of a 6-inch
downlight that exceeds the performance of typical
42‑watt compact fluorescent lamp (CFL) products.
The design uses cree’s Xlamp cXa2520 leD, a multi-
die, high‑flux array optimized for high lumen output
applications such as downlights, recessed fixtures
and can lights. The cXa2520 offers lighting-class
performance and reliability in a single, easy-to-use
component.
Six-inch downlights are the industry standard indoors
and outdoors in both residential and commercial
applications such as soffits and ceilings, where a wide
beam pattern is desirable. with a typical light output
range from 1500 to 3600 lumens, the flexibility, high
performance and ease of use offered by the Xlamp
cXa2520 leD makes it a strong candidate for use in a
6-inch downlight.
www. cree.com/Xlamp
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.
of Cree, Inc. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.
2
XLamp CXa2520 LED
6-inCh DownLight
REfEREnCE DEsign
Importance
Characteristics
Luminous flux (steady‑state)
Efficacy
units
lumens (lm)
lumens per watt (lm/W)
critical
luminous distribution
color uniformity
Form factor
price
manufacturability
lifetime
hours
degrees (°C)
% relative humidity
K
100-point scale
$
Important
operating temperatures
operating humidity
Correlated color temperature (CCT)
Color rendering index (CRI)
ease of installation
table 2: some ranked design criteria for an LED downlight
Table 3 and Table 4 summarize the ENERGY STAR requirements for luminaires.
3
EnERgy stAR REquIREmEnts
Luminaire type
Downlights:
•
recessed
•
surface
•
pendant
•
SSL downlight retrofits
Luminaire Efficacy (Initial)
42 lm/w
Luminaire minimum Light
Output (Initial)
≤ 4.5” aperture: 345 lumens
> 4.5” aperture: 575 lumens
Luminaire Zonal Lumen
Density Requirement
luminaire shall deliver a minimum
of 75% of total initial lumens within
the 0‑60° zone (axially symmetric
about the nadir)
table 3:
ENERGY STAR luminous efficacy, output and zonal lumen density requirements
Characteristic
Light source life requirements:
all luminaires
Requirements
The LED package(s) / LED module(s) / LED array(s), including those incorporated into LED light engines or
GU24 based integrated LED lamps, shall meet the following L70 lumen maintenance life values (refer to Lumen
Maintenance Requirements in the next section):
•
•
•
25,000 hours for residential grade indoor luminaires
35,000 hours for residential grade outdoor luminaires
35,000 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.
3
ENERGY STAR® Program Requirements, Product Specification for Luminaires (Light Fixtures), Eligibility Criteria, Version 1.2,
of Cree, Inc. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.
3
XLamp CXa2520 LED
6-inCh DownLight
REfEREnCE DEsign
Characteristic
lumen maintenance
requirements: directional and
non-directional luminaires
Requirements
The LED package(s) / module(s) / array(s), including those incorporated into LED light engines or GU24 based
integrated leD lamps, shall meet the following l
70
(6k) rated lumen maintenance life values, in situ:
•
•
l
70
(6k) ≥ 25,000 hours for residential indoor
l
70
(6k) ≥ 35,000 hours for residential outdoor, or commercial
compliance with the above shall be documented with a Tm-21 lumen 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 device, and the in situ TMP
leD
temperature of the hottest LED in the luminaire. In addition to LM‑80 reporting requirements, the following
information shall be reported:
•
•
•
•
•
•
sampling method and sample size (per LM‑80 section 4.3)
test results for each T
S
and drive current combination
description of device including model number and whether device is an LED package, module or array (see
Definitions)
ANSI target, and calculated CCT value(s) for each device in sample set
Δ u’v’ chromaticity shift value on the CIE 1976 diagram for each device in sample set
a detailed rationale, with supporting data, for application of results to other devices (e.g. LED packages with
other CCTs)
access to the Tmp
leD
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
luminaires
The luminaire (directional luminaires), or replaceable LED light engine or GU24 based integrated LED lamp (non‑
directional luminaires) shall have one of the following nominal CCTs:
•
•
•
•
•
2700
3000
3500
4000
5000
Kelvin
Kelvin
Kelvin
Kelvin
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.
Color rendering requirements:
all indoor luminaires
color angular uniformity
requirements: directional solid
state indoor luminaires
color maintenance
requirements: solid state indoor
luminaires only
The luminaire (directional luminaires), or replaceable LED light engine or GU24 based integrated LED lamp (non‑
directional luminaires) shall meet or exceed Ra ≥ 80.
Throughout the zonal lumen density angles detailed above, and five degrees beyond, 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 be within 0.007 on the CIE 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 a comparison of luminaire chromaticity data in LM‑79 reports at zero and 6,000 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 6,000 hours.
Source start time requirement:
directional and non-directional
luminaires
Power factor requirements:
directional and non-directional
luminaires
light source shall remain continuously illuminated within one second of application of electrical power.
Total luminaire input power less than or equal to 5 watts: PF ≥ 0.5
Total luminaire input power greater than 5 watts:
Residential: PF ≥ 0.7
Commercial: PF ≥ 0.9
Ballast or driver shall comply with aNSI/Ieee c62.41.1-2002 and aNSI/Ieee c62.41.2-2002, class a operation.
The line transient shall consist of seven strikes of a 100 kHz ring wave, 2.5 kV level, for both common mode and
differential mode.
Frequency ≥ 120 Hz
Note: This performance characteristic addresses problems with visible 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
of Cree, Inc. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.
4
XLamp CXa2520 LED
6-inCh DownLight
REfEREnCE DEsign
Characteristic
Noise requirements: directional
and non-directional luminaires
Requirements
All ballasts & drivers used within the luminaire shall have a Class A sound rating.
Ballasts and drivers are recommended to be installed in the luminaire in such a way that in operation, the
luminaire will not emit sound exceeding a measured level of 24 Ba.
table 4: EnERgy stAR luminaire requirements
2.
DEfInE DEsIgn goALs
Typical 42-w cFl downlights use a lamp that produces about 3100 lm, but luminaire light output is only about 2000 lm,
giving a fixture efficiency of about 65%. We chose the design goals for this project, shown in Table 5, to better this
performance using less energy over a longer lifetime. We chose a 50° cutoff angle as a good balance between maximizing
direct illumination and minimizing glare. As shown in Figure 1, the cutoff angle is measured from the vertical axis of the
luminaire outward to the point at which the brightness of the light source is no longer visible.
light source
cutoff angle
figure 1: Cutoff angle
Characteristic
light output
Luminaire efficacy
cutoff angle
lifetime
ccT
crI
power
power factor
unit
lm
lm/w
degrees
hours
K
100-point scale
w
minimum goal
2000
75
50
35,000
3000
80
26
0.9
target goal
> 2000
> 75
50
50,000
3000
> 80
< 26
> 0.9
table 5: Design goals
3.
ESTImATE EffIcIENcIES Of ThE OpTIcAL, ThERmAL & ELEcTRIcAL SYSTEmS
We used Cree’s Product Characterization Tool (PCT) tool, shown in Figure 2, to determine the drive current for the
design.
4
For the 2000‑lumen target, we estimated 90% optical efficiency and 87% driver efficiency. We also estimated a solder
of Cree, Inc. For product specifications, please see the data sheets available at www.cree.com. For warranty information, please contact Cree Sales at sales@cree.com.
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