LED Testing Standards Overview

Transcription

1 Meeting and Measuring ENERGY STAR Requirements 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

2 Outline Background Relative vs. absolute photometry LED photometric testing standards: IES LM IES LM IES TM IES LM General questions and answers

3 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 CFL 3

4 Relative and Absolute Photometry 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) Comfortable and accurate at 25 C, but how to take measurements at 85 C? 4

5 Relative and Absolute Photometry 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

6 Standard Test Methods for LED Products Standard Method Purpose IES LM Absolute Light output, efficacy, color for LED products IES LM Relative Light output over time, temperature for LED packages IES LM Relative (references LM-79) Light output, efficacy, color over temperature for light engines IES TM Calculation, modeling Extrapolating LM-80 test data to predict life ANSI/UL 153:2002 (Secs A) ANSI/UL 1574:2004 (Sec. 54) ANSI/UL 1598:2008 (Secs. 19.7, ) Portable Electric Luminaires Track Lighting Systems Luminaires Methods for in-situ temperature method (ISTM) testing for EnergyStar

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

8 Scope LM 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. 8

9 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 9

10 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 V < Vin < V 10

11 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 hrs with 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 11

12 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 % 12

13 Test of an SSL Downlight Product Input Power (W) Relative Light Output Input Power Light Output Time (min) 13

14 Test of an SSL Downlight Product % Input Power (W) Efficacy by 2.3% Over next 12 hours 0.9% Relative Light Output Input Power Light Output Time (min) 12 14

15 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 orientation Orientation 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 15

16 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

17 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% 17

18 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. Goniophotometer a) Most use photometer head b) Spectroradiometer needed for color measurements 18

19 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

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

21 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 21

22 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

23 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 < a single, directional measurement with a spectroradiometer suffices for color. Else 23

24 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

25 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 colormeasuring 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 25

26 IES LM Approved Method for Lumen Maintenance Testing of LED Light Sources

27 Scope IES LM 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 27

28 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 L 70 : time to 70% lumen maintenance L 50 : time to 50% lumen maintenance Case temperature Temperature of the thermocouple attachment point on the LED source defined by manufacturer 28

29 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 100% Light Output 70% 50% 0% L 70 L 50 Time 29

30 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 30

31 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% 31

32 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) 32

33 IES TM Projecting Long Term Lumen Maintenance of LED Light Sources

34 IES TM Scope: Provides a recommendation for projecting long term lumen maintenance of LED light sources using LM lumen maintenance data

35 IES TM Projection method: Data: LM 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 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., IES TM Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, IES TM 21 11

36 IES TM times rule based on confidence band, which is determined by: Number of samples Uncertainty of measurement system over time Miller, C., IES TM Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, 2011.

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

38 IES TM Projection method (cont d): Data used for curve-fit show that using hour data vs ,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, C., IES TM Overview, History and Q&A Session. EPA ENERGY STAR Lamp Round Table, San Diego, CA, Oct. 24, Tuttle, R. et al., TM 21 Update: Method for Projecting Lumen Maintenance of LEDs. CORM 2011 Technical Conference. (Miller, 2011)

39 IES TM Projection method: Curve-fit ( t) B exp( t) 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

40 IES TM Projection method (cont d): Curve-fit L p ln(100 B p ) For example: L p = lumen maintenance life expressed in hours where p is the percentage of initial lumen output that is maintained. L 70 B ln( ) 0.7 IES TM When α>0, the exponential curve fit decays to zero, L p >0 (valid calculation) When α<0, the exponential curve fit increases, L p <0 (invalid calculation, 6 times rule will apply)

41 IES TM Temperature interpolation Interpolate Lp C) between Ts,1 (55 C) and Ts,2 (85 C) 55 C 70 C?? 85 C Arrhenius equation to calculate in situ decay rate constant. (After Tuttle et al., 2011) i E Aexp( k T B a s,i ) A = pre exponential factor; E a = activation energy (in ev); T s,i = in situ absolute temperature (in K); k B = Boltzmann s constant (8.6173x10 5 ev/k) Tuttle, R. et al., TM 21 Update: Method for Projecting Lumen Maintenance of LEDs. CORM 2011 Technical Conference.

42 IES TM Description of LED Light Source Tested (manufacturer, model, catalog number) 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) Tested case temperature (⁰C) - 55 C Table 1: Report at each LM-80 Test Condition Test duration used for projection (hour to hour) - Test duration used for projection (hour to hour) - Tested case Tested case - temperature (⁰C) temperature (⁰C) - α - α - α - B - B - B - Calculated L70(Dk) Calculated L70(Dk) Calculated L70(Dk) - - (hours) (hours) (hours) - Reported L70(Dk) Reported L70(Dk) Reported L70(Dk) - - (hours) (hours) (hours) - TM 21calculator (After Tuttle et al., 2011) 85 C C 70 C?? 85 C (projection based on in-situ temperature entered) T s,1 (⁰C) - T s,1 (K) - α 1 - B 1 - T s,2 (⁰C) - T s,2 (K) - α 2 - B 2 - E a /k b - A - B 0 - T s,i (⁰C) - T s,i (K) - 55 C 85 C 70 C α i - Projected L70(Dk) (hours) - Reported L70(Dk) (hours) calculator

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

44 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

45 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.

46 Why LM-82-12? Luminaire photometry is less meaningful for end-users of decorative luminaires y CIE Chromaticity Diagram 1931 Black Body Locus White Shade Blue Shade Amber Shade Decorative Glass Shade WAC Lighting luminaires tested by LRC x Glass shade Vin (V) Pin (W) Ф (lm) Efficacy (lm/w) x y CCT (K) CRI White Blue Amber Highly decorative Alex Baker and Taylor Jantz Sell, ENERGY STAR Luminaires Specification. ENERGY STAR Luminaires Conference Call, March 9, 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.

47 IES LM ASSIST recommends formed the basis for LM 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 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

48 LM vs. LM Scope LM LED light engines Integrated LED lamps LM LED luminaires Integrated LED lamps ENERGY STAR Luminaires v1.1 Testing ambient temperature For non-directional luminaires LED light engines GU24 integrated LED lamps At different temperatures (*UUT T b : T b ±2 C) For directional luminaires 25 C±1 C *UUT stands for unit under test; T b stands for UUT manufacturer specified temperature monitoring point temperature

49 IES LM 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 T b : UUT T d : driver AE709D7BBC43E004EB6A7FF.prgav06?R=4HGL3

50 Thermal test chamber: LED light engines LED/LED array Temperature sensor (Ts) Heat Sink Driver Temperature sensor (Td) Heater Insulation 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.

51 Thermal test chamber: LED light engines Example inside integrating sphere

52 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. Flux (lm) CIE x,y Life (L70) (hrs) Ts ( C) Ts ( C) Ts ( C)

53 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) Flux (lm) CIE x,y Life (L70) (hrs) Ts ( C) Ts ( C) Ts ( C)

54 IES LM Φ(lm) T in situ P (W) T in situ Simple curve fit Linear Exponential Etc. T room T room+25 C T room+δt T room T room+25 C T room+δt x T in situ y T in situ CCT (K) T in situ T room T room+25 C T room+δt T room T room+25 C T room+δt T room T room+25 C T room+δt

55 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 Measured temperature of T b (or T d ) 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 T room T room +25 C T room +ΔT Initial Temperature First Elevated Temperature (Initial+25 C) Second Elevated Temperature (per Test Requesters)

56 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.

57 Acknowledgements NYSERDA for sponsoring this event Acuity Brands Lighting for hosting the event Jessica Lloyd LRC faculty, staff, and students ASSIST program sponsors

58 Thank you