Create Meaningful Performance Metrics for LED Systems

Transcription

1 Create Meaningful Performance Metrics for LED Systems by N. Narendran, Ph.D. Lighting Research Center Rensselaer Polytechnic Institute, Troy, NY Alliance for Solid-State State Illumination Systems and Technologies euroled 2007 Birmingham, UK June 5 th

2 Acknowledgments euroled organizers LRC faculty, staff, and students Jean Paul Freyssinier, Yimin Gu, Lalith Jayasinghe, Jennifer Taylor, Martin Overington, Tianming Dong, Yiting Zhu, and Huying Wu LRC s project sponsors ASSIST Program Sponsors 2

3 Outline The current state of LED technology Device and system performance Application trends in general illumination Reliability considerations Why there is a need for technology-independent performance testing and metrics How best to compare lighting products for performance, regardless of the light source inside Introduction to ASSIST Recommended fixture testing methods, as outlined by ASSIST recommends 3

4 Introduction to LEDs

5 LED LED Will soon be one of the light source choices for illumination applications. The potential for reduced energy use and lower maintenance costs are two key attributes of this rapidly evolving technology that have generated so much interest for its use. 5

6 Industry Trend Growing number of LEDs and LED fixtures 6

7 High-power LED Higher flux per device Higher efficiency Better color properties for white LEDs Good color rendering Much lower color variation between lamps More stable color over time Longer life Lamina Devices from: Lumileds, OSRAM Opto, Nichia, CREE, Lamina Ceramic, Seoul Semiconductor 7

8 Commercial products (April 2007) White LED products: Efficacy ranges from 20 to 90 lm/w Lumen output ranges from 20 to 100 lm per single die devices Please see manufacturers data sheet 8

9 New class of LEDs AC LED AC operation (120V/240V) No need for drivers 9

10 LED life Some LEDs are delivering on the 100,000 hrs promise However, there is significant variation between products Narendran - LRC 10

11 Failed promise Long life is one of the features of LED technology In these cases, the LED systems did not live up to their promise. 11

12 Applications

13 Trends in LED applications Illumination applications targeted by the LED community in the near term are: Indoor - Undercabinet lighting Indoor - Directional lighting (downlights) Outdoor - Street and parking lot lighting 13

14 Directional lighting applications

15 Directional lighting Increasing interest for using LEDs in directional lighting applications. Presently, there are many light sources available to cater to these applications. Incandescent Halogen CFL HID LED 15

16 Are LEDs suitable for directional lighting? Directional lighting products experience a wide range of environmental conditions: Ventilated Semi-ventilated Fully enclosed Heat at the LED junction increases as the ventilation around the LED is reduced 16

17 Impact of heat on LEDs Heat negatively affects the performance of LEDs. Life (hrs) Light output Color Life (~ half the life for every 10 deg C) R 2 = T-point Temperature (deg C) Relative light output 1 Watt White LEDs 110% 100% 90% 80% 70% 60% Tj LED A LED B LED C 17

18 LED fixture performance LED fixtures generally have several high-power LEDs grouped together to attain the light levels needed for the application. In residential and hospitality applications, downlights produce about 600 lumens. With increased number of LEDs the amount of heat generated also increases Without sufficient heat sinking the LED performance could suffer Therefore, maximum light output attainable in a fixture without sacrificing performance depends on the application environment 18

19 Installation Issues Even a properly heat sunk LED fixture can perform badly in insulated spaces. Halogen / Incandescent Fixture LED Fixture Insulation material above the ceiling area Conducted heat Radiant heat Ceiling tiles (Poor thermal conductor) 19

20 Evaluating directional lighting products A laboratory study was conducted to analyze the maximum light output attainable from presently available LED downlights In this study a test LED downlight fixture was tested at temperatures similar to application conditions: Ventilated, Semi-ventilated, and Fully enclosed UL test setup for temperature testing was used for creating the test environments. Open-air, Non-IC, and IC 20

21 Test fixture Test LED fixture Multiple LED arrays 1, 4, 10, LEDs can be turned on selectively Two types of commercial white LEDs were used in this study Rated for 1W and 3W operation 21

22 Light output measurement setup To measure the total light output, the test fixture was set up in the Flux-O-Meter The test fixture was placed inside the UL test boxes to mimic application conditions Open air Non-IC IC Fixture in open air Fixture in an IC test box Detector 22

23 Test Results LED type % Relative light output Open air Relative flux 1000% 500% Non-IC IC 0% Watts 3W white LEDs, 35 lm/w Tpin (deg C) LED Pin temp. Open air Non-IC IC Watts 23

24 LED Life Based on data collected, the estimated life of the LEDs (L 70 ) at 60 C board temperature is 35,000 hrs. 60,000 LRC Life Data Life in hour (L70) 40,000 20, Board temperature Tb (deg C). 24

25 Test Results LED type 1 Estimated maximum lumens from a fixture rated at 35,000 hrs life Open air ~ 492 lm Non-IC ~ 390 lm IC ~ 210 lm Estimated efficacy (without the driver) Open air ~ 22 lm/w Non-IC ~ 22 lm/w IC ~ 21 lm/w Creating IC rated fixtures with this type of LED is not feasible. Relative flux 1500% 1000% Tpin (deg C) 500% 0% Relative light output Watts LED Pin temp Watts Open air Non-IC IC Open air Non-IC IC 25

26 Test Results LED type 2 Estimated maximum lumens 1200% Relative Flux Open air ~ 880 lm IC ~ 320 lm Estimated efficacy (no driver) Open air ~ 65 lm/w Relative flux 800% 400% 0% wattage Open air IC IC ~ 60 lm/w LED type 2 had much better performance. IC rated fixtures can be created with this type of LED with longer life. Tpin LED Pin temp. Open air IC wattage 26

27 Comparison of different technologies Watts needed to produce 600 lm per fixture Power (W) to yield 600 lm per fixture 90 W INC 1 CFLs 75 W LED 3 - IC INC Power (W) 60 W 45 W INC 2 LED 3 LED 1 - IC INC 3 LED 1 - air LEDs 30 W LED 2 LED 4 CFL 2 15 W CFL 1 0 W 0 lm/w 20 lm/w 40 lm/w 60 lm/w 80 lm/w 100 lm/w Lamp efficacy (lm/w) 27

28 Cost initial cost At the present time, most LED lighting fixtures have a higher initial purchase cost than incandescent or fluorescent fixtures (approximately 3 to 10+ times higher) Downlights: Incandescent 75W ~$50 CFL ~$90 to $140 LEDs PC ~$300 to $500 28

29 Cost What is the lifecycle cost of an LED system? Why life cycle cost? Consumers are more aware of costs beyond initial purchasing cost. A meaningful way to compare systems with different Initial and installation costs Operation costs (energy, relamping, other maintenance) Operational lifetimes 29

30 Life-cycle cost The following cost estimates are based on the assumption that LED systems would last 50,000 hrs or longer Residential Application Hospitality Application Total Cost for 10yrs $3,500 $3,000 $2,500 $2,000 $1,500 $1,000 $500 $0 Inc 1 Inc 2 Inc 3 CFL 1 CFL 2 LED 1 LED 2 LED 3 30 Total Cost for 20yrs $7,000 $6,000 $5,000 $4,000 $3,000 $2,000 $1,000 $0 Inc 1 Inc 2 Inc 3 CFL 1 CFL 2 LED 1 LED 2 LED 3

31 LED life 100% Light Output 90% 80% Half the life for every 10 deg C increase 70% Hours Ts Thermocouple Life (hrs) R 2 = T-point Temperature (deg C) 31

32 A sample commercial fixture A commercial LED lamp (RGB) operated in open air and an IC-rated downlight fixture Over 100 C temperature rise in an IC rated fixture Large color shift (appears green) Such a lamp may not last even 5,000 hrs Board Temp. of a LED PAR30 Lamp Temperature (C) Time (hrs) Open IC 32 Jayasinghe et al. 2006

33 Summary LEDs in directional lighting Some of the presently available LEDs can cater to certain lighting applications In the case of directional lighting, they are more suitable for open air operation Track lights, surface mount lights, etc In recessed applications the LEDs would have much shorter life. Presently, LED systems cost higher than traditional lighting systems. They are more cost competitive in commercial applications than residential applications (life-cycle cost), assuming 50,000 hrs life. With rapidly improving performance and decreasing cost of LEDs, these systems will become more cost effective in the future 33

34 Street and parking lot lighting applications

35 Street lighting Street lighting aims to satisfy different needs: driver and pedestrian safety increased sense of security aesthetics economic development reduced light pollution and light trespass reduced operating cost energy efficient and longer life 35

36 Are LEDs suitable for street lighting? Example: Comparison between typical high-pressure sodium (HPS) and LED products: Assumptions: 1000-ft stretch of a two 12-ft lane street pavement reflectance of 7 percent (R3) illuminance requirements per RP-8-00 local and collector roads with low, medium and high pedestrian activity 70-W or 150-W HPS IES distribution type III mounting height of 32-ft 2-ft setback and 4-ft arm length, and calculations consider initial values only (i.e., no lamp lumen depreciation) 1000-ft Type III distribution 4-ft 2-ft 32-ft 36

37 IESNA RP-8 8 Standard Recommended illuminance and uniformity ratios for different roadway and street lighting conditions. IES road definitions: Collector. The roadways serving traffic between major and local roadways. These are roadways used mainly for traffic movements within residential, commercial, and industrial areas. Local. Roadways used primarily for direct access to residential, commercial, industrial, or other abutting property. They do not include roadways carrying through traffic. Long local roadways are generally divided into short sections by a system of collector roadway systems. Illuminance and uniformity criteria to meet Illuminating Engineering Society of North America American National Standard Practice for Roadway Lighting. RP New York: Illuminating Engineering Society of North America. 37

38 Product comparison - 1 Fixture A 70-W or 150-W HPS semi cutoff cobra head Efficiency (down/up) 78% / 3% Efficiency (street/house) 60% / 21% Lumens per lamp 6800-lm (70-W) lm (150-W) Fixture power 85-W (70-W) 189-W (150-W) Fixture C 36 1-W white LEDs Efficiency (down/up) 99% / 0% Efficiency (street/house) 51% / 49% Lumens per lamp 925-lm Fixture power 53-W Mounting height = 32-ft Mounting height = 32-ft 38

39 Number of poles and total power needed to meet RP-8-00 criteria 70-W HPS fixture 150-W HPS fixture 1-W LED fixture (36 LEDs) Differential Road type Pedestrian activity Number of poles Total power Number of poles Total power Number of poles Total power # Poles Power Low - Residential W 70-W lamp is a better option W 320% 191% Local Medium - Intermediate W 70-W lamp is a better option W 344% 205% High - Commercial 150-W lamp is a better option 6 1,134 W W 700% 196% Low - Residential 150-W lamp is a better option 7 1,323 W W 371% 104% Collect or Medium - Intermediate 150-W lamp is a better option 7 1,323 W W 600% 168% High - Commercial 150-W lamp is a better option 7 1,323 W W 957% 268% 39

40 Product comparison - 2 Fixture A 150-W HPS semi cutoff cobra head Efficiency (down/up) 78% / 3% Efficiency (street/house) 60% / 21% Lumens per lamp lm (150-W) Lumens per fixture lm (150-W) Fixture power 189-W (150-W) Fixture D W white LEDs Efficiency (down/up) Efficiency (street/house) NA NA Lumens per fixture 11,200-lm Fixture power 188-W Mounting height = 20-ft Mounting height = 20-ft 40

41 Cost Initial cost Outdoor fixtures 150 W MH ~$150 to $300 HPS ~$150 to $200 LED ~$700 to $1,500 41

42 Products compared Fixture A 150-W HPS semi cutoff cobra head Efficiency (down/up) 78% / 3% Efficiency (street/house) 60% / 21% Lumens per fixture Fixture power lm (150-W) 189-W (150-W) Fixture D W white LEDs Efficiency (down/up) NA Efficiency (street/house) NA Lumens per fixture 11,200-lm Fixture power 188-W Lumen Maintenance Values for HPS, MH and a White LED lumen maintenance (%) 100% 90% 80% 70% 60% 400W HPS 400W MH Life cycle cost of LED systems could be lower due to reduced relamping and servicing. 50% Hi-LED operating time (hr) 42

43 Summary Street lighting Presently, some LED fixtures are starting to compete with HID light sources for area and street lighting where low light levels are required. Parking lot and parking garage lighting are easier targets for LEDs than street lighting Value propositions for LEDs are longer life and group relamping. If the LED fixture life is not 50,000 hrs or greater then the life cycle cost will be much more expensive compared to traditional light fixtures 43

44 Metrics and Measurement Methods

45 Why Metrics? Metrics allow users to quantify and compare performances. To make meaningful comparisons between products, performance metrics developed for lighting applications must be technologyindependent. 45

46 Metrics Presently, there are many metrics to quantify performance of light sources and fixtures. Efficacy: Lumens per watt Color: CRI, CCT, Chromaticity coordinates Life Many specifications assume the performance of the lamp (or lamp-ballast combination), tested under an ideal environment, as the performance of the complete fixture. 46

47 Performance Metric - Efficacy Light source efficacy ideal condition Lamp/driver efficacy ideal condition Fixture efficacy ideal condition Fixture efficacy application condition 47

48 Setting expectations 48

49 Test methods To obtain realistic performance data for a lighting fixture, the test environment must mimic the actual environment where it would be used. Question: How do we do that? If we understand the factors that influence performance, then a test setup can be developed to test fixtures. 49

50 Introduction ASSIST

51 History & Background Established: In 2002 Goal: To support the development and widespread application of LEDs for general illumination. Identify and reduce the major technical hurdles currently facing solid-state lighting Activities: Industry collaboration, research, demonstration, and education 51

52 ASSIST Program Sponsors 52

53 ASSIST Recommends ASSIST recommends is a program of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST). When standard definitions and metrics for LED technology are not available, ASSIST develops and publishes recommendations. The recommendations are developed through research conducted on behalf of ASSIST by the LRC. ASSIST Recommends helps manufacturers present meaningful information to end users in a consistent manner. ASSIST also publishes application guidelines to help end-users select and apply LED technology successfully. 53

54 Industry activities Standards-setting organizations such as NEMA, CIE, ANSI, IESNA.and others have been working on certain standards. ASSIST is conducting research to develop information that can be useful for metrics and setting standards. ASSIST Recommends 54

55 ASSIST Recommends The first ASSIST Recommends, LED Life for General Lighting was released in 2004 Life definition: 70% lumen maintenance (50% for indicators or decoration) Life reported by both LED and fixture manufacturers 55

56 LED life definition ASSIST recommends end-of-life lumen maintenance values of: 70% for general lighting (L 70 ) L 70 = 30% reduction in light output 50% for decorative lighting (L 50 ) Light Output 100% 70% 50% 0% Time L 50 = 50% reduction in light output Color-shift during this time must be within a 4-step MacAdam ellipse 56

57 Measuring life ASSIST encourages manufacturers to provide life data, in hours, at L70 and L50 for both: Components (individual LEDs) Systems (LEDs with housing, driver, optics, etc.) Measure at rated current for at least 6,000 hours LED components measured at three temperatures High-power LEDs: Ts = 45 C, 65 C, 85 C Low-power LEDs: Ts = 35 C, 45 C, 55 C Thermocouple Ts = temperature of closest measurement point to the LED junction (usually the solder joint) LED systems measured at: Ts temperature corresponding to application environment 57

58 Estimating life Two steps for providing life data: Measure light output at rated current for at least 6,000 hours (longer is better) Use data between 1,000 and 6,000 hours to extrapolate life beyond 6,000 hours 58

59 Sample life-test data Exponential data fit, omitting the initial 1000 hrs 3E-05 Degradation Rate 2E-05 y = 5E-10e 0.184x R 2 = E-05 0E Board Temperature (deg C) 59

60 Estimating life (I/Io) = 1 exp (-a) t Where a is the degradation rate I/Io is the relative light output If 70% relative light output is defined as life L 70 = [ln (0.7)/(-a)] Example: y = e-5.25 x 10-6 L70 = [ln(0.7)/5.72 x 10-7] = 67,938 hrs 60

61 Data comparison Different products have different degradation rates Degradation rate as a function of board temperature is also different for different products 61

62 Consistent Reporting 62

63 Current status Some of the LED manufacturers are already collected and reporting data per ASSIST Recommends. Several organizations have referenced LED life ASSIST Recommends NEMA DOE IES 63

64 New ASSIST Recommends publications 1. Under-cabinet Lighting 2. Directional lighting

65 New documents 3-parts General guide to applications Guide to selecting LED fixtures Testing and evaluation recommendations Audiences Guides Homeowners, general contractors Testing and evaluation Manufacturers, standards-setting bodies, state and federal agencies, public benefit program administrators, independent test labs 65

66 ASSIST Recommends Under-cabinet Lighting Proposed test method

67 Goal To recommend a method for testing and evaluating the photometric and life performance of white light under-cabinet fixtures for all light source technologies Performance data accurately represents fixture performance in application Performance data meets end user expectation 67

68 Evaluation Top performance criteria for end-users Amount of luminous flux illuminating the task area Total fixture power Color of the light within the optical beam System life when used in an application These are influenced by the fixture design 68

69 References ASSIST ASSIST recommends : LED life for general lighting. Troy, NY : Lighting Research Center. IESNA IES Guide for the Selection, Care and Use of Electrical Instruments in the Photometric Laboratory, IESNA LM New York: Illuminating Engineering Society of North America. IESNA Approved Method for Photometric Testing of Indoor Fluorescent Luminaires, IESNA LM New York: Illuminating Engineering Society of North America. IESNA IESNA Guide to Lamp Seasoning, IESNA LM New York: Illuminating Engineering Society of North America. IESNA Approved Method for Life Testing of Incandescent Filament Lamps, IESNA LM New York: Illuminating Engineering Society of North America. IESNA Approved Method for Photometric Testing of Indoor Luminaires Using High Intensity Discharge or Incandescent Filament Lamps, IESNA LM New York: Illuminating Engineering Society of North America. Jayasinghe, L., Y. Gu, and N. Narendran Characterization of thermal resistance coefficient of high-power LEDs. Sixth International Conference on Solid State Lighting, Proceedings of SPIE 6337, 63370V. National Lighting Product Information Program. In press. CFL residential downlights. Troy, NY: Lighting Research Center. Rea, M.S., ed IESNA Lighting Handbook: Reference and Application, 9th ed. New York: Illuminating Engineering Society of North America. 69

70 Proposed Method For task lighting, application efficacy is more meaningful than source or fixture efficacy The proposed method considers the application environment and the light delivered to the task area rather than the ideal environment for the lamp and light exiting the fixture 70

71 Proposed method Calculate application efficacy using near-field photometry Small distance between UC light source & task plane calls for near-field photometry Amount of flux illuminating the task plane is the most useful, not all the flux that exits the luminaire Application efficacy = Total lumens on the task Total fixture power 71

72 Proposed Method Determine color Use CCT, CRI, and CIE x,y provided by light source manufacturer Measure fixture life Follow life-testing guidelines from ASSIST recommends: LED Life for General Lighting 72

73 Proposed apparatus Proposed apparatus emulates the application environment Under-cabinet Testing Alcove Plywood construction in common cabinet, backsplash, and counter sizes Cabinet length extends 12 in. beyond luminaire on each side Task area color - Black Under-cabinet luminaire 12-inch 12-inch 12-inch 18-inch 24-inch 73

74 Testing proposal High source efficacy does not guarantee high application efficacy What matter is the light on the task area 6-inch 6-inch φ = (φv + φh) / W φ i = E i. A i φv = Ev. Av ; φh = Eh. Ah Application Efficacy = φ / W (lm/w) 74

75 Test Data Properly designed and built fixtures have higher application efficacy Some LED fixtures have higher application efficacy than linear fluorescent lamp fixtures in this application Efficacy (lm/w) % 74% 54% 81% 85% Halogen F8T5-1 F8T5-3 LED 1 LED 2 Fixture Efficacy Application Efficacy 75

76 Sample manufacturer s s data sheet Some manufacturers already report illuminance data on a grid: a 10 by 10 grid 76

77 Summary For under-cabinet fixtures Application efficacy is a more meaningful criterion for system comparison Light where you need it Near-field photometry more relevant Application efficacy is influenced by the fixture design Some undercabinet LED fixtures have higher application efficacy than linear fluorescent lamp fixtures. 77

78 Summary One important consideration for undercabinet fixtures Fixture replacement Can we get an identical replacement after several years? Or do we have to replace all the fixtures because one segment failed? 78

79 ASSIST Recommends Recommendations for Testing and Evaluating Luminaires Used in Directional Lighting

80 Goal To recommend a method for testing and evaluating the photometric and life performance of directional lighting fixtures. Performance data accurately represents fixture performance in application Performance data meets end user expectation 80

81 Proposed method Test entire fixture at temperatures similar to application conditions Ventilated (open-air) Semi-ventilated (non-ic) Fully enclosed (IC) Measure temperature (Ts) when operating the fixture in a given condition For LEDs, Ts is the board or pin temperature (fixture manufactures should provide the thermocouple attachment point) Operate fixture in the measurement setup at the same temperature (Ts) while gathering data Sphere photometry Goniophotometry 81

82 Test setup for temperature testing UL test setup for temperature testing can be used for creating the test environments. Open-air, Non-IC, and IC 82

83 Sphere photometry Place fixture inside a heated enclosure Test enclosure is similar to the enclosure used for testing directional lights in a sphere. Gather data once the Ts temperature reaches application temperature Test enclosure 83

84 Test enclosure for sphere photometry Test enclosure includes heaters to maintain proper Ts operating temperature Heated enclosure Heater Td Ballast/driver Complete fixture Ts Lamp Feedback control 84

85 Goniophotometry Place downlight in the test environment (open air, non-ic, IC) UL test box is used for creating the non-ic, IC conditions Gather flux data after stabilization Fixture in open air Fixture in an IC test box Detector 85

86 Pilot Study #1 Results At pin temperature (Ts) 62 C Measured flux (Flux-o-meter): 304 lumens Measured flux from the sphere: 307 lumens Results from the two setups matched within 1% LED Fixture flux (lm) vs Tpin 350 Lumens y = -0.86x R 2 = Pin Temperature (deg C) Sphere measurements Flux-o-meter measurement 86

87 Pilot Study #2 A commercial RGB PAR lamp was operated in the three environments open air, Non-IC and IC and the respective Ts temperature values were measured. Next, the same RGB PAR lamp was operated in the test enclosure inside the sphere, and measurements were taken at the same Ts values. Ts IC ~ 160 C Ts Non-IC ~ 90 C Ts Open-air ~ 60 C 87

88 Pilot Study #2 Results Knowing the Ts values for the PAR lamp, performance in any operating environment can be measured. Par 30 LED CIE xy values Flux (lm) 320 y = x R 2 = CIE x,y y = x R 2 = y = x R 2 = CIE x CIE y Board Temp (deg C) Board temp. (deg C) y CIE x y CIE x 88

89 Summary Photometric and life performance data of directional lighting fixtures measured in test environments mimicking the actual environment are more useful for end users. Fixture performance would meet end user expectation It is feasible to create test environments mimicking the actual environment where the fixtures would be used in order to obtain realistic performance data for a lighting fixture. Although shown for LED systems, a similar approach can be taken for CFLs. 89

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