LED Photometry Testing Considerations

LED Photometry Testing Considerations

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Description: LED Photometry Testing Considerations by Apec work shop, for the promotion and application of LED lighting technology. Measurement system reliability considerations when conducting long-term photometry testing by Yiting Zhu Ph.D. And N.

Narendran, ph.D. - Lighting Research Center. .

 
Author: Yiting Zhu, Ph.D. (Fellow) | Visits: 3098 | Page Views: 3745
Domain:  Green Tech Category: Lighting Subcategory: test 
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Contents:
Measurement System Reliability
Considerations When Conducting
Long-term Photometry Testing
Yiting Zhu, Ph.D. and N. Narendran, Ph.D.
Lighting Research Center
Rensselaer Polytechnic Institute
Troy, NY 12180, U.S.A.

Acknowledgments
• 2011 APEC LED Workshop Organizers
• LRC faculty, staff, and students
• ASSIST Program sponsors

3

Outline
• LED technology update
• Long-term testing of LED systems
– Lumen depreciation
– Catastrophic failure

• Summary
4

Light source technologies
• Of all the light source technologies, solidstate light sources have the highest potential
for energy-savings
THERMAL
Lamp
Type

Efficacy
(lm/W)
NOW
Efficacy
Limits
(lm/W)

INCANDESCENT
Filament &
Filament &
inert gas
halogen gas

12

26
50

ELECTRIC DISCHARGE
SOLID STATE
HIGH INTENSITY DISCHARGE LIGHT EMITTING DIODES
FLUORESCENT
Linear
Compact
Quartz Metal- Ceramic Metal- Inorganic: LED
Organic:
(Circleline)
(CFL)
halide
halide
OLED

90-110

60

120

100-115
280

Modified after Walter P. Lapatovich,
OSRAM SYLVANIA

5

130

120-130
340

25-50

LED Downlights
From Energy Star® Web site, May 2011
COMMERCIAL downlights

90
80

80
Luminaire efficacy (lm/W)

Luminaire efficacy (lm/W)

RESIDENTIAL downlights

90

70
60
50
40
30
20

70
60
50
40
30
20

10

10

0

0
0

750 1500 2250 3000 3750 4500

0

Light output (lm)

750 1500 2250 3000 3750 4500
Light output (lm)

6

Service Life


LED system performance in terms of light output and luminous
efficacy has improved
– Not all systems perform well
– Good performers can compete effectively with legacy light source
technologies in some applications like downlighting



Life of LED systems is not well known
– LM80 data for LED is not suitable to predict LED system life
• A system has many components
– LED/array, secondary lens, driver, etc.

– Presently, there is no industry-agreed definition for system life or
accelerated test method for predicting system life



Product Warranty is important
– To gain consumer confidence
7

Long-Term Performance of LED System
• Similar to LEDs, systems also
have two types of failure
– Lumen depreciation
• Slow light output degradation over time

– Catastrophic failure
• Cease to produce light

8

Lumen depreciation measurement of
LED System

9

LED System Long-Term Testing
• Lumen depreciation
– Heat affects LED system performance

• ASSIST recommends 2007:
– Measure luminaire performance in conditions similar to
application environment.
– Three environmental conditions to test systems:
• Open air: Here the light source and the driver have plenty
of ventilation around them.
• Semi-ventilated: Here the light source and the driver have
limited ventilation around them (similar to non-IC)
• Enclosed: Here the light source and the driver have almost
no ventilation around them (similar to IC)

10

Long-term testing of LED Systems

11

Lumen Depreciation
IC

• In the IC condition:
– L70 is less than 3000 hours

Non-IC

Open air

119 °C

107 °C

87 °C

Fixture B - 26W LED Downlight
110%

Relative Light Output

100%
90%
80%
70%
60%
50%
100

Enclosed

1,000
Time (hours)
Semi-ventilated
12

10,000

Open air

Long term testing challenges
• For systems that last a long time, to achieve reliable
long-term photometric test results, it is essential that
the measurement system be reliable.
• Possible Failures:
– Test setup
• Heater controller
• Thermocouple
• Heater

– Measurement equipment error
• Ambient temperature fluctuation
• Room humidity fluctuation

13

Possible instrument failures
Heater controller
• Heated test box
– Pin temperature is
used as the input to
the heater controller

• Heater controller
failed and the IC test
box overheated and
the luminaire failed

14

Possible instrument failures
Thermocouple
• The thermocouple
used for monitoring
the pin temperature
of the LED failed

t
u 100%
p
t
u 80%
O
t 60%
h
g
i 40%
L
e 20%
v
i
t
a 0%
l
e
0
R
Open air

Fixture G

10000
Time (hrs)
Semi-ventilated

20000
Enclosed

Fixture G
120
) 100
C
g 80
e 60
d
(
n 40
i
p 20
T
0
0
Open air
15

5000

10000
Time (hrs)
Semi-ventilated

15000

20000

Enclosed

Fixture C

Environmental Influence
• Data for 3 different
downlight systems

t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

10‐4‐2007

110%
90%
70%
50%
0

10000

20000

30000

40000

Time (hrs)
Open air

Fixture D

– Lumen output fluctuations

• Is it due to environmental
factors

t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

90%
70%
50%
0

10000

20000

30000

Open air

Fixture F

3‐24‐2009

110%
90%
70%
50%
0

10000

20000
Time (hrs)
Open air

16

40000

Time (hrs)

t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

• Ambient temperature?
• Humidity?

10‐24‐2007

110%

30000

40000

Fixture C

Environmental Influence
• Even though the downlights
were set on the test rack at
different times, the lumen
out fluctuation trend tracks
each other very well

t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

10‐4‐2007

110%
90%
70%
50%
0

10000

20000

30000

40000

Time (hrs)
Open air

Fixture D

10‐24‐2007

110%
t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

90%
70%
50%
0

10000

20000

30000

40000

Time (hrs)
Open air

Fixture F

3‐24‐2009

110%
t
u
p
t
u
O
t
h
g
i
L
e
v
i
t
a
l
e
R

90%
70%
50%
0

10000

20000
Time (hrs)
Open air

17

30000

40000

Summary
• Long-term lumen depreciation
measurement data for LED downlights
– The longer the data collection period the
greater the likelihood for instrumentation
failure
– Lumen fluctuation patterns
• Work in progress to determine cause

18

Catastrophic Failure Measurement of
LED System

19

Study Objective
• To develop an accelerated test method that
can predict the failure of LED luminaires
under realistic operating conditions
(catastrophic failure instead of light output
depreciation failure).
– This method should predict lifetime based on
factors such as: application temperature, on-off
cycling, and others if applicable.

20

Background
• Rapid-cycle stress test
• 2 min ON / 2 min OFF

• LRC study showed that 2 min ON / 2 min OFF
introduces only a small T, and therefore the
damage that leads to failure may be small.

21

Background
• Real-life light fixture cycling pattern:
– Office: 6am to 6pm (12 hrs on, 12 hrs off)
– Home: 6am to 10am, 6pm to 10pm (4 hrs
on, 4 hrs off)

• Preliminary studies identified the
following acceleration parameters:
– ΔT, Max. Tj, Ramp rate, Dwell time

22

Study Objective
Thermal Condition

#1

#2

12hrs on

25°C

25°C

Max. T

95°C

110°C

ΔT

70°C

85°C

Dwell time*

0,1,2,3,4,5,6,7,
8,9

0,1,2,3,4,5,6,7,
8,9

Ramp rate*

0.6°C/min

1.2°C/min

4hrs on

Time to failure (TTF)

Min. T

0

0.5hr

1hr

1.5hrs

10.5hrs

Dwell time
(Predicted TTF-Dwell time correlation)

23

Tests in progress
• Determine the relationship
between time to failure and
– T max
– ΔT
– Ramp rate

• Accelerated tests are expected
to last a few months
• Realistic condition tests are
expected to last 2-3 years
24

Conclusions
• Long-term testing
– Reliable test equipment is critical
– Needs frequent calibration to compensate for environmental factors
• Example: reflectance properties of integrating sphere paint

• Highly accelerated testing
– Pros
• Shorter testing time
• Less concerns about test equipment failure

– Cons
• Could introduce failure mechanisms that may not be present in real life
conditions
– Predict shorter life

25

Thank you.

26