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Capturing the Lighting Edge – August 13, 2012 New York, NY© 2012 Rensselaer Polytechnic Institute. All rights reserved.

LED Testing Standards Overview

Presented by: Andrew Bierman, MS and Jean Paul Freyssinier, MS with contributions from Yiting Zhu, PhD and N. Narendran, PhD

Lighting Research Center, Rensselaer Polytechnic Institute, Troy, NY, USA

Meeting and Measuring ENERGY STAR® Requirements


Outline

Background› Relative vs. absolute photometry

LED photometric testing standards:› IES LM-79-08› IES LM-80-08› IES TM-21-11› IES LM-82-12

General questions and answers


Relative and Absolute Photometry

Relative Photometry:› Output is relative to an easily-measured

condition› E.g., bare lamp operated on a reference

ballast, base up at 25°C› Specific lamp performance doesn’t matter

Absolute photometry:› Output is measured in calibrated units

under specific operating and environmental conditions

• Orientation• Input voltage• Ambient temperature

› Lamp and system performance matters

3

CFL



Absolute is more difficult because: Need to maintain flux standards and calibrate equipment

› Calibrate with incandescent, measure other SPDs and directional light sources

Sampling concerns› How many? How to choose? Are samples representative?

Must reproduce environmental and operating conditions while maintaining calibrated equipment› Temperature, input voltage or current (driver)

4

Comfortable and accurate at 25° C, but how to take measurements at 85° C?



Relative photometry is used to simplify testing› Works well when the system is well defined and characterized

• E.g., linear fluorescent lamp systems– Flux = (rated lumens) x (ballast factor) x (luminaire efficiency)

› Does not work well for making comparisons across different systems

• E.g., CFL replacements for incandescent lamps– Geometry issues, lack of reference ballast definitions, temperature

effects

› Useful for measuring variations under different testing conditions

• Light output over time• Elevated temperature

5


Standard Test Methods for LED Products

Standard Method Purpose

IES LM-79-08 Absolute Light output, efficacy, color for LED products

IES LM-80-08 Relative Light output over time, temperature for LED packages

IES LM-82-12 Relative (references LM-79)

Light output, efficacy, color over temperature for light engines

IES TM-21-11 Calculation, modeling Extrapolating LM-80 test data to predict life

ANSI/UL 153:2002 (Secs. 124-128A) ANSI/UL 1574:2004 (Sec. 54) ANSI/UL 1598:2008 (Secs. 19.7, 19.10-16)

Portable Electric LuminairesTrack Lighting Systems

Luminaires

Methods for in-situ temperature method (ISTM) testing for EnergyStar


IES LM-79-08Approved method: Electrical and Photometric Measurements of Solid-state Lighting Products

Capturing the Lighting Edge – August 13, 2012 New York, NY© 2012 Rensselaer Polytechnic Institute. All rights reserved. 8

Scope LM-79-08

Solid-state lighting products for illumination purposes Complete systems with electrical drivers and heat sinks

› Powered by AC mains or dc voltage Measurements under standard conditions

› Total luminous flux› Electrical power, input voltage and current› Luminous intensity distribution› Chromaticity, correlated color temperature (CCT), Color Rendering Index

(CRI) Luminaires (including light source) and integrated LED lamps

› e.g., recessed down lights (must include light source)› e.g., A-lamp replacements

Methods for individual product performance. Does not cover how individual variations affect performance.


Ambient Conditions

Air Temperature› 25°C ±1°C› Measured at the same height as the fixture› Shielded from direct radiation

Thermal Conditions for Mounting SSL Products› Heat conduction through supporting objects must be negligible › If sample is provided with a support structure used for thermal

management, then the sample shall be tested with the support structure attached

Air Movement› Keep airflow around SSL sample to a minimum› Should only be natural convection air current from sample operation


Power Supply Characteristics

Waveshape of AC power supply› Shall have a sinusoidal shape with ≤ 3% distortion of the

fundamental frequency

Voltage regulation±0.2% of the rated value

For a product rated at 120V

119.76V < Vin < 120.24V


Seasoning of SSL Products

No seasoning of samples prior to testing

› The test committee determined this method would produce the most repeatable results

Other light sources

› Incandescent lamps: 0.5% of rated life

› Fluorescent lamps: 100 hrswith 3-hr on and 20-min off cycle

› HID: 100 hrs with 11-hr on and 1-hr off operating cycle

Initial lumen maintenance of LEDs


Stabilization of SSL Products

Stability based on both input power and light output

Stability is when the variation of at least 3 readings over a period of 30 min, taken 15 min apart, is less than 0.5 %


Test of an SSL Downlight Product

10.00

10.05

10.10

10.15

10.20

10.25

10.30

10.35

10.40

10.45

10.50

0 10 20 30 40 50 60 70 80

Time (min)

Inpu

t Pow

er (W

)

12

12.1

12.2

12.3

12.4

12.5

12.6

Rel

ativ

e Li

ght O

utpu

t

Input PowerLight Output


Test of an SSL Downlight Product

10.00

10.05

10.10

10.15

10.20

10.25

10.30

10.35

10.40

10.45

10.50

0 200 400 600 800 1000

Time (min)

Inpu

t Pow

er (W

)

12

12.1

12.2

12.3

12.4

12.5

12.6

Rel

ativ

e Li

ght O

utpu

t

Input PowerLight Output

1.4%

0.9%

Efficacy by 2.3%Over next 12 hours


Operating Orientation

Shall be evaluated in the orientation recommended by the manufacturer for an intended use of the sample

Stabilization and photometric measurements of SSL products shall be done in such operating orientation

Note: The light emission process of an LED is not affected by orientationOrientation can change the thermal conditions for the LEDs used in the product, and so…The light output may be affected by orientation of the SSL product


Electrical Settings

Operated at rated voltage according to its normal use› No pulsed operation

If the product has dimming capability, measurements shall be performed at the maximum input power condition

If the product has multiple modes of operation including variable CCT, measurement may be made at different modes of operation (and CCTs) if necessary, and such setting conditions shall be clearly reported

16


Electrical Instrumentation

Instrumentation Calibration Uncertainties (u)

Expanded uncertainty: 2-sigma, 95% confidence

ac voltage and current u ≤ 0.2%

ac power u ≤ 0.5%

dc voltage and current u ≤ 0.1%


Test Methods for Total Luminous Flux Measurement

Two options

1. Integrating Sphere a) with spectroradiometer

b) with photometer head (requires spectral mismatch error correction – not trivial)

2. Goniophotometera) Most use photometer head

b) Spectroradiometer needed for color measurements


Sphere geometry

4 Geometry› total SA of product should be <2% of

the total SA of the sphere wall (20 cm cube for 2-m sphere!)

› longest dimension of a product should be < 2/3 sphere diameter

2 Geometry› opening diameter should be less than

1/3 of the sphere diameter› mounted within the circular opening in

such a way that its front edges are flush with the edges of the opening

IES-LM-79-08


Goniophotometer

Primarily used for the measurement of the luminous intensity distribution of lamps and luminaires

www.npl.co.uk

www.intertek-etlsemko.com


Goniophotometer measurements

LM-79 specifies type C goniometers› Burning position of the sample is

unchanged relative to gravity› Minimal impact of thermal

performance of sample Two sub-types

› Moving detector› Moving mirror

The speed of rotation should be such as to minimize the disturbance of the thermal equilibrium of the sample

Relative photometry method, commonly used in traditional luminaire testing, cannot be used for SSL products with integral lamps


Colorimetric calculations

The chromaticity coordinates (x, y) and/or (u’, v’ ), and correlated color temperature (CCT, unit: kelvin) are calculated from the relative spectral distribution› Commission Internationale de l'Eclairage, Colorimetry, 3rd edition,

CIE 15:2004

The Color Rendering Index (CRI) is calculated according to the formulae defined in› Commission Internationale de l'Eclairage, Method of Measuring and

Specifying Colour Rendering of Light Sources, CIE 13.3-1995


Spatial non-uniformity of chromaticity

Products may have variation of color with angle of emission Spatial non-uniformity of chromaticity shall be evaluated

› The spatial non-uniformity of chromaticity, u’v’ , is determined as the maximum deviation among all measured points from the spatially averaged chromaticity coordinate

› distance on the CIE (u’, v’ ) diagram

For this evaluation, accuracy only in chromaticity differences is critical, and thus, measurements may be made with a tristimulus colorimeter if a spectroradiometer is not available

If u’v’ < 0.001 a single, directional measurement with a spectroradiometer suffices for color. Else …


12.2 Method using spectroradiometer or colorimeter spatially scanned

Manually positioning the instrument for given directions at a constant distance

Shall be measured at› ≤10° intervals for vertical

angle over the angle range where light is intentionally emitted from the source

› Minimum two horizontal angles =0° and 90°

The chromaticity measurements need to be made only for the angles where the average luminous intensity is >10% of the peak intensity

IES-LM-79-08


Method using spatially scanned spectroradiometer or colorimeter

May be used when› Sphere-spectroradiometer system is not available

› Test sample is too large for a sphere-spectroradiometer system

Can be achieved most efficiently by mounting the color-measuring instrument on a goniometer › Called gonio-spectroradiometer, or gonio-colorimeter

Luminous intensity distribution and chromaticity coordinates can be measured at the same time› taking readings at appropriate angle intervals over the entire angle

range where the light is intentionally emitted from the product

› Then, the spatially averaged chromaticity is obtained from all measured points by spatially-integrated tristimulus values


IES LM-80-08 Approved Method for Lumen Maintenance Testing of LED Light Sources


Scope IES LM-80-08

Measuring lumen maintenance for LED› Packages› Arrays› Modules

Does not provide guidance or make any recommendations regarding predictive estimations or extrapolation beyond that from actual measurements (TM-21 covers this)

CREE LED Supply CREE


Definitions

LED light source› An LED package, array, or module that is operated via an auxiliary driver

Lumen maintenance› Luminous flux output at any selected elapsed operating time› Usually expressed as a percentage of the maximum output)

Lumen maintenance life› Elapsed operating time at which the specified lumen maintenance is reached

Rated lumen maintenance› L70: time to 70% lumen maintenance› L50: time to 50% lumen maintenance

Case temperature› Temperature of the thermocouple attachment point on the LED source

defined by manufacturer


LED Life Definitions

› 70% for general lighting, illumination (L70)• L70 (hrs) = 30% reduction in light output

› 50% for decorative lighting, indicators (L50)• L50 (hrs) = 50% reduction in light output

29

Time

Ligh

t O

utpu

t

100%

0%

70%

50%

L70 L50


General Conditions

Conduct test in clean environment

Individual labeling of LED sources

Representative sampling of LEDs and report sampling method

Minimize vibration (although not nearly as sensitive as other lamp types)

Minimize airflow, but do not allow thermal stratification

Operating orientation and spacing› Orient as specified by manufacturer

› Space to allow air flow around units


Temperature and humidity

A minimum of 3 case temperatures› 55°C› 85°C› The third is at the discretion of the manufacturer

Temperature tolerance +0, -2° C Air temperature surrounding case within +0, -5°C Relative humidity < 65%


Electrical and instrumentation

Current maintained ± 3% during life test› ± 0.5% during photometric testing

Thermocouple accuracy limits: ≤ 1.1°C or 0.4%

Elapsed time uncertainty within ± 0.5%

Photometric measurements performed at 25 ± 2°C

Test duration› At least 6000 hours, preferably 10,000 hours

› Photometry every 1000 hours minimum

Operating cycle› Constant current (no modulation, e.g. PWM)


IES TM-21-11 Projecting Long Term Lumen Maintenance of LED Light Sources


IES TM-21-11

Scope: › Provides a recommendation for projecting long

term lumen maintenance of LED light sources using LM-80-08 lumen maintenance data

34


IES TM-21-11

Projection method:› Data: LM-80-08 report

• 6000-hour data with 1000-hour interval• Less than 1000-hour interval is encouraged• Data beyond 6000 hours is encouraged

› Sample size: • 20 units for a multiplication factor of 6• 10-19 units for a multiplication factor of 5.5• Not applied for sample size less than 10

units› Normalization:

• Normalize all collected data to 100% at 0 hour for each DUT

› Average• Average the normalized measured data of

all samples• Miller, C., 2011. IES TM‐21‐11 Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, 2011.

IES‐TM‐21‐11


IES TM-21-11

6 times rule based on confidence band, which is determined by: › Number of samples› Uncertainty of measurement system over time

• Miller, C., 2011. IES TM‐21‐11 Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, 2011.


IES TM-21-11

Projection method (cont’d):› Data used for curve-fit

• 6,000 h <Test duration (D)< 10,000 h– Last 5000 hours of data is used– Data before 1000 hours shall not be used

since many LEDs experience rapid changes during the first 1000 hours

• Test duration (D)> 10,000 h– Last 50% of the total test duration shall be

used

(Miller, 2011)• Miller, C., 2011. IES TM‐21‐11 Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, 2011.• Tuttle, R. et al., 2011. TM‐21 Update: Method for Projecting Lumen Maintenance of LEDs. CORM 2011 Technical Conference.


IES TM-21-11

Projection method (cont’d):› Data used for curve-fit

• show that using 1000-6000 hour data vs. 5000-10,000 hour give different lifetime predictions

• later data show more characteristic decay curve of interest

– Non-semiconductor related decay (encapsulant, etc.) occurs early on

– Later decay is semiconductor degradation-related and can be considered as classic exponential decay

– Long duration data sets (>10,000 h) show better verification

(Miller, 2011)• Miller, C., 2011. IES TM‐21‐11 Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, 2011.• Tuttle, R. et al., 2011. TM‐21 Update: Method for Projecting Lumen Maintenance of LEDs. CORM 2011 Technical Conference.


IES TM-21-11

Projection method:› Curve-fit

)exp()( tBt

• t = operating time in hours• (t) = averaged normalized luminous flux output at time t

• B = projected initial constant derived by the least squares curve‐fit

• α = decay rate constant derived by the least squares curve‐fit

IES‐TM‐21‐11


IES TM-21-11

Projection method (cont’d):› Curve-fit

)100ln(pB

Lp

Lp = lumen maintenance life expressed in hours where p is the percentage of initial lumen output that is maintained.

)7.0

ln(70

B

L

For example:

• When α>0, the exponential curve‐fit decays to zero, Lp>0 (valid calculation)

• When α<0, the exponential curve‐fit increases, Lp<0 (invalid calculation, “6 times” rule will apply)

IES‐TM‐21‐11


IES TM-21-11

Temperature interpolation› Interpolate Lp (@Ts,i=70C) between Ts,1 (55C) and

Ts,2 (85C)

A = pre‐exponential factor;Ea = activation energy (in eV);Ts,i = in‐situ absolute temperature (in K);kB= Boltzmann’s constant (8.6173x10‐5 eV/K)

)exp(,isB

ai Tk

EA

(After Tuttle et al., 2011)Arrhenius equation to calculate in situ decay rate constant.

• Tuttle, R. et al., 2011. TM‐21 Update: Method for Projecting Lumen Maintenance of LEDs. CORM 2011 Technical Conference.

55C

85C

70C??


IES TM-21-11

Sample size - Sample size - Sample size -

Number of failures - Number of failures - Number of failures -DUT drive current used in the test (mA)

- DUT drive current used in the test (mA)

- DUT drive current used in the test (mA)

-

Test duration (hours) - Test duration (hours) - Test duration (hours) -

Test duration used for projection (hour to hour)

- Test duration used for projection (hour to hour)

- Test duration used for projection (hour to hour)

-

Tested case temperature (⁰C)

- Tested case temperature (⁰C)

- Tested case temperature (⁰C)

-

α - α - α -B - B - B -Calculated L70(Dk) (hours)

- Calculated L70(Dk) (hours)

- Calculated L70(Dk) (hours)

-

Reported L70(Dk) (hours) -



Table 1: Report at each LM-80 Test Condition

Description of LED Light Source Tested (manufacturer, model,

catalog number)

Ts,1 (⁰C) -

Ts,1 (K) -

α1 -

B1 -

Ts,2 (⁰C) -

Ts,2 (K) -

α2 -

B2 -

Ea/kb -

A -B0 -

Ts,i (⁰C) -

Ts,i (K) -

αi -Projected L70(Dk) (hours) -


(projection based on in-situ temperature entered)

55C

85C70C??

55C

55C

85C

85C

70C

(After Tuttle

et a

l., 2011)

www.energystar.gov/TM‐21calculator

www.energystar.gov/TM‐21calculator


IES LM-82-12Approved method: Characterization of LED Light Engines and LED Lamps for Electrical and Photometric Properties as a Function of Temperature

LED Light Engines LED Lamps


Decorative luminaires

Commonly used in residential and hospitality applications

Can provide a coordinated look while serving different functions › Sconces, chandeliers, pendants, table

and floor lamps › Available in a variety of shapes, styles

and finishes

Combine “fashion with function,” ….according to the American Lighting Association

www.americanlightingassoc.com/about_news_detail.php?id=2


LED industry trend

Manufacturers often design families of decorative luminaires: › Sconces, pendants, table and floor lamps› These luminaires can provide a coordinated look while serving

different functions

A large number of decorative luminaires can use a common light source (LED light engine).

Photometric testing of complete fixtures is not a feasible concept for such luminaires.


Why LM-82-12?

Luminaire photometry is less meaningful for end-users of decorative luminaires

• Alex Baker and Taylor Jantz‐Sell, 2011. ENERGY STAR Luminaires Specification. ENERGY STAR Luminaires Conference Call , March 9, 2011. • ASSIST, Recommendations for Testing and Evaluating White LED Light Engines and Integrated LED Lamps Used in Decorative Lighting Luminaires, Volume 4, Issue 1, revised April, 2009.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1x

y

CIE Chromaticity Diagram 1931Black Body LocusWhite ShadeBlue ShadeAmber ShadeDecorative Glass Shade

WAC Lighting luminaires tested by LRC

Glass shade Vin (V) Pin (W) Ф (lm) Efficacy (lm/W) x y CCT (K) CRI

White 120.1 4.48 165.0 36.8 0.3929 0.3876 3761 73.6Blue 120.1 4.48 129.9 29.0 0.3468 0.3698 4998 72.0

Amber 120.0 4.48 82.6 18.4 0.4507 0.4129 2851 69.0Highly decorative 120.1 4.48 34.9 7.8 0.4499 0.3942 2711 78.1


IES LM-82-12

ASSIST recommends formed the basis for LM-82-12. › LED performance (luminous flux, life) largely depends on the

LED junction temperature, which varies depending on how the LED is integrated into the luminaire and the installation environment.

LM-82-12 requires testing the performance of the LED light engine and the integrated lamp as a function of temperature, so the performance at in situ temperature can be predicted:› Power (W)› Luminous flux (lm)› Color


LM-82-12 vs. LM-79-08

LM-82-12 LM-79-08

Scope • LED light engines• Integrated LED lamps

• LED luminaires• Integrated LED lamps

ENERGY STAR Luminaires v1.1

For non-directional luminaires LED light engines GU24 integrated LED lamps

For directional luminaires

Testing ambient temperature

At different temperatures(*UUT Tb: Tb±2°C)

25°C±1°C

*UUT stands for unit under test; Tb stands for UUT manufacturer‐specified temperature monitoring point temperature


IES LM-82-12

Thermal environment› Mounting the UUT to a thermoelectric cooler (TEC)› Mounting the UUT in a temperature chamber that only

controls the local environment around the UUT

Temperature measurement› Tb: UUT› Td: driver

www.cree.comhttp://m.grainger.com/mobile/details/;jsessionid=A011BDF9B

AE709D7BBC43E004EB6A7FF.prgav06?R=4HGL3

Tb: UUT Td: driver


Thermal test chamber: LED light engines

Temperature sensor (Td)Driver

LED/LED array

Heat Sink

Heater Insulation

Temperature sensor (Ts)

Test chamber – painted white on the outside

ASSIST, Recommendations for Testing and Evaluating White LED Light Engines and Integrated LED Lamps Used in Decorative Lighting Luminaires, Volume 4, Issue 1, revised April, 2009.


Example inside integrating sphere

Thermal test chamber: LED light engines


Proposed method

First, the LED light engine performance is measured as a function of temperature.› LED light engine is placed inside a thermal test chamber.› The heater is turned on until Ts reaches 40% (and 60% and 80% )

of Tj max (specified by the LED manufacturer)› Photometric and electric quantities and life are measured at these

three temperatures.

Ts (°C)

Flux (lm)

Ts (°C)

CIE x,y

Ts (°C)

Life (L70) (hrs)


Ts (°C)

Flux (lm)

Ts (°C)

CIE x,y

Ts (°C)

Life (L70) (hrs)

Proposed method

Estimating light engine performance in a luminaire› Temperature Ts is measured while the light engine is

operating in a luminaire in its operating environment.› The performance parameter is estimated from the

plots generated during the engine’s characterization.

Thermocouple(Ts)


IES LM-82-12

Troom Troom+25°C Troom+ΔT

Φ(lm

)

Tin‐situ

Troom Troom+25°C Troom+ΔTP (W

)

Tin‐situ


x Tin‐situ


y Tin‐situ


CCT (K)

Tin‐situ

“Simple curve fit”• Linear• Exponential• Etc.


IES LM-82-12:Test report

Test date, facility, equipment, and operator

UUT description (manufacturer, description, catalog number)

If applicable, UUT driver description (manufacturer, description, catalog number, input and output parameters)

Description of test method including testing configuration.

Internal procedure reference

Initial Temperature First Elevated Temperature (Initial+25°C)

Second Elevated Temperature (per Test Requesters)

Measured temperature of Tb (or Td)

Input power (W)

Input voltage (V)

Input current (A)

Luminous flux (lm)

Luminous efficacy (lm/W)

CIE chromaticity (x,y or u’,v’)(optional)

Correlated color temperature (K)(as optional)

Uncertainties



Summary

Heat management is critical to LED performance› Short and long term: color shift, lumen depreciation

Performance of bare LEDs is not predictive of the system’s performance

Testing luminaires under realistic conditions (as a function of environment temperature) provides more useful information to end users and designers

SSL testing standards aim to measure LEDs and LED systems under repeatable conditions, but still may not provide all the information needed in the field.


Acknowledgements

NYSERDA for sponsoring this event

Acuity Brands Lighting forhosting the event› Jessica Lloyd

LRC faculty, staff, and students

ASSIST program sponsors


Thank you

led testing standards overview - lrc.rpi.edu · led testing standards overview ... › commission...

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