led luminaires - economical lifetime and service concepts, june 2011

Schréder, Steffen Holtz, June 2011LEDs – Economical Lifetimes

LED luminaires – Economical Lifetimes


LED System

LED luminaires are part of an integrated system

thermal

electronic optical

mechanical


High Power LEDs

LED types used by Schréder LED lifetime extrapolation (TM-21) LED system lifetime LED driver lifetime LED exchange concepts


LED Concepts

CitizenCL-L 103-longitudinal

Cree XP-E1mm2-chip

Bridgelux RS4500 lm

Cree MC-E4x0.7mm2-multichip

Cree XM-L4mm2-chip

Difficult to use forasmmetric

street lighting pattern


LED Lifetime – Tests and Extrapolations


Among the findings of the TM-21 workgroup:

6000 hours of LM-80 testing is not adequate to allow accurate projection of L70

LED platforms from manufacturer to manufacturer each tend to have their own lumen depreciation characteristics

LED platforms within a given manufacturer each tend to have their own lumen depreciation characteristics

LED Lifetime Extrapolation – TM-21


2. Chip Degradation

1. Silicone Encapsulant Degradation

3. Phosphor Degradation

FACTORS AFFECTING LUMEN DEPRECIATION IN LEDs

Ceramic Substrate, Silicone Encapsulant, Phosphor Conversion


2. Chip Degradation

1. Silicone Encapsulant Degradatio



Molded Plastic Package, Silicone Encapsulant, Phosphor Conversion, Silver Lead Frame

4. Lead Frame Degradation5. Plastic Degradation


1. Silicone Encapsulant Degradation

2. Chip Degradation


4. Reflector Degradation

5. Glass Degradation


Ceramic Substrate, Silicone Encapsulant, Phosphor Conversion,Silver Reflector, Glass Lens


time

Lumen Depreciation of LED Components

chip degradation


time


chip degradation

silicone degradation


time


chip + silicone degradation


time


chip + silicone degradation

plastic degradation


time


chip + silicone + plastic degradation


Typical LM-80 Test Behavior and TM-21 Lumen Maintenance Projection (6k)

• First 1k hours is ignored for TM-21 projection purposes• Upper reporting bound set by 6x available data (6 x 6k = 36k hrs)• Exponential extrapolation to least squares mathematical fit between 1k and 6k

hours• Reported and projected L70 may or may not be the same number

100%

90%

80%

70%

Lum

en M

ainte

nanc

e (%

)

Time (hours)

10,000 20,000 30,000 40,000 50,000

Projected L70(6k) = 35,000 hoursReported L70(6k) = 35,000 hours

6 x 6,000 = 36,000 hours (max)



100%

90%

80%

70%

Lum

en M

ainte

nanc

e (%

)

Time (hours)

10,000 20,000 30,000 40,000 50,000

6 x 10,000 = 60,000 hours (max)


• Tmax/2 is used for TM-21 projection (10K/2 = last 5K hours)• Upper reporting bound set by 6x data (6 x 10k = 60k hrs)• Exponential Extrapolation to least squares mathematical fit between 5k and 10k




100%

90%

80%

70%

Lum

en M

ainte

nanc

e (%

)

Time (hours)

10,000 20,000 30,000 40,000 50,000

6 x 20,000 = 120,000 hours (max)


• Tmax/2 is used for TM-21 projection (20K/2 = last 10K hours)• Upper reporting bound set by 6x data (6 x 20k = 120k hours)• Exponential Extrapolation to Least squares mathematical fit between 10k and 20k



LED Lifetime – Tests and Extrapolations

Tj=68 °C, 0.35 A Tj=98 °C, 0.35 A

Tj=112 °C, 0.7 A

Low impact of thecurrent on lumen

maintenance

L70=148 Kh L70=67 Kh

L70=54 Kh


Lumen Maintenance and Catastrophic Failures

Tj: Impact on critical failuresIf: Impact on lumen maintenance (L70)

Lumen maintenanceEx. Cat. failures

Catastrophic failures65 °C

100 °C


Lumen Maintenance– From the LED to an LED Luminaire

B10, L70

B50, L70

L70, only regarding long-term lumen maintenance


Failure Rates – LED System Approach

LED tunnel luminaire (54 LEDs)

Requirement in the customer‘s specification:90 % lumen maintenance in 90 % of all luminairesafter 5 years of operation (24 h/day) 44000 h

What will be the maximum Tj in order to fulfil this requirement? At a given Tj, what is a realistic failure rate?

Long-TermLumen Maintenance

CatastrophicFailure Rate

System Life

Monte-Carlo-Simulation



62 LEDs110 °C

90 khrs vs. 60 khrs!!!

L70



350mA/54 LEDs/L80

Tj = 65°C

Tj = 75°C

Tj = 80°C

Tj = 85°C

90,00080,000



L70L75L80L90

350mA/54 LEDs/65°C


Critical Failures

LEDs fail !!!

Probability of the failure of an individual LED after 50000 h:0,05 % - 0,5 % (depending on the operating conditions)Luminaire with 32 LEDs Probability that at least one LED fails after 50000 h can be 15 %Failure modes and preventive actions: Open circuit: The LEDs in a series are off protection by a shunt (Zener)

Short circuit: Only the defective LED is offno additional protection

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LED Drivers – Lifetime and Reliability

LEDs: Lifetime (Byy, Lxx)

Drivers: Failure rate as a function of lifetime

Failu

re ra

te/ti

me

unit



Typical lifetime curve of electronic driversUsable lifetime



Typical lifetime curve of electronic drivers

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

30 40 50 60 70 80 90 100

Life

time

Ambient temperature [ C]

Driver Lifetime vs. Temperature

Lifetime ~ eEa/RT

(Arrhenius Law)

Reference: Tc at the Tc point indicated on the driverTc ≠ Ta !!

Impact of temperature ifthe driver is not operated?


MTBF-MTTF

Calculation of the lifetime of electronic devices

MTBF: Mean Time Between FailuresPredicted elapsed time between inherent failures of a system during operation

MTBF Simulation taking into account: Components Current Temperature of the components Air humidity

No repair of a defective System MTTF: Mean Time To Failure

MTBF

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MTBF-Lifetime

MTBF ≠ Lifetime

Failures at MTBF: 63 %!!!(assuming exponential failure model)

Lifetime of typical drivers: OSRAM OT42/350 5 % failures at 50000 hrs VS-O EDXe 350-40W 10 % failures at 50000 hrs ROAL 42 V 120 V 350 mA 8 % failures at 80000 hrs H&S 84 W+126 W 120 V 8 % failures at 80000 hrsOnly statistical failures, no catastrophic failure due tothe end of capacitor lifetime

5 % failures at 50000 hrs ≈ 1000000 hrs MTBF


Failure Modes in the LED System

Other failure causes in the LED luminaire

Thermal

Electronic

Optical Browning of the

lensed due to heatand UV Soiling

Mechanical Solder cracks due to

mismatch of expansioncoefficients


AR

ESA

LED

OR

IEN

TOLED Exchange Concepts

PCB accessible, exchange of the PCB


CALLA LEDFuture proof!

• Onsite replacement concept

• Electronic & LED optical block

• Adapted to the follow the LED evolution

LED Exchange Concepts

Exchange of the LED module


PIANO

• LEDSafe®: performances over time- Completely IP 66 sealed LED Optical bloc - LEDs + lenses protected by a glass- Extra-clear glass

Optical bloc IP 66 independant and removable on site

• FutureProof:- onsite replacement concept- electronic & LED optical bloc- adapted to follow the LED evolution

LED Exchange Concepts

Exchange of the whole optical block

led luminaires - economical lifetime and service concepts, june 2011

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