Can the present white LEDs cater to the lighting needs?

Transcription

1 tssl 2007 June 15-16, 2007 Taipei, Taiwan Can the present white LEDs cater to the lighting needs? N. Narendran, Jean Paul Freyssinier, and Yimin Gu Lighting Research Center Rensselaer Polytechnic Institute Troy, NY 12180

2 Acknowledgements tssl organizers LRC staff ASSIST Program sponsors LRC s solid-state lighting project sponsors 2

3 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 3

4 Trends in illumination applications Illumination applications targeted by the LED community in the near-term are: Indoor Directional lighting (downlights) Outdoor Street and parking lot lighting 4

5 Directional lighting applications

6 Directional lighting Increasing interest for using LEDs in directional lighting applications. Presently, there are many light sources available to cater to these applications. Are LEDs ready for this application? Incandescent Halogen CFL HID LED 6

7 LED fixture performance LED fixtures generally have several high-power LEDs grouped together to attain the light levels needed for the application. Requires about 600 lm per downlight fixture. With an increased number of LEDs, the amount of heat generated also increases. Without sufficient heat sinking, the LED performance will suffer. Therefore, the maximum light output attainable in a fixture without sacrificing life depends on the application. 7

8 Installation Issues Even a properly heat sinked LED fixture can perform poorly in insulated spaces. Applications have to be selected carefully for LEDs to succeed. Halogen / Incandescent Fixture LED Fixture Insulation material above the ceiling area Conducted heat Radiant heat Ceiling tiles (Poor thermal conductor) 8

9 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 directional lighting fixture was tested per ASSIST Recommends ( : Ventilated, Semi-ventilated, and Fully enclosed 9

10 Test Results LED type % Relative light output Open air Relative flux 1000% 500% Non-IC IC 0% Watts Tpin (deg C) LED Pin temp. Open air Non-IC IC Watts 10

11 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). 11

12 Test Results LED type 1 Estimated maximum lumens 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 would not be feasible unless the life is sacrificed significantly. As an example, for 20 C more, an ICrated fixture can produce up to 390 lm, but the life will be reduced to 15,000 hrs. 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 12

13 Test Results LED type 2 Estimated maximum lumens 1200% Relative Flux Open air ~ 880 lm IC ~ 320 lm Relative flux 800% 400% Open air IC Estimated efficacy (no driver) 0% Open air ~ 65 lm/w wattage IC ~ 60 lm/w 80 LED Pin temp. Much better performing ICrated fixtures can be created with this type of LED with longer life. Tpin wattage Open air IC 13

14 Example: Downlighting Generally, downlight fixtures used in residential, office, and hospitality applications produce around 600 lumens per fixture. In 2007, the power demanded by some commercial LED fixtures is approaching that of CFL downlight fixtures. In the future, LED fixtures could become more energy efficient than CFL fixtures. However, there are many commercial LED fixtures with very poor performance. Watts to yield 600 lm per fixture Fixture power (W) CFLs INC LEDs Fixture efficacy (lm/w) 14

15 Initial Cost At the present time, most LED lighting fixtures have a higher initial purchase cost than incandescent or fluorescent fixtures (approximately 3 to 6 times higher). Downlights: Incandescent 75W ~$50 CFL ~$90 to $140 LEDs PC ~$300 to $500 15

16 What is the lifecycle cost of an LED system? Why lifecycle cost? Consumers are becoming 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 Two sample applications were used for estimating lifecycle cost Residential 16 ft x 16 ft (110 lx to 180 lx on the task) Hospitality 16 ft x 16 ft 16

17 Cost in a residential kitchen What is the lifecycle cost of an LED system? light source lamp type (number of fixtures) average horizontal illuminance power per kitchen (W) initial purchase cost ($) A19 75W (4) 113 lx 300 W $ 212 INC R30 75W halogen (4) 157 lx 300 W $ 212 PAR38 55W HIR (4) 195 lx 220 W $ 212 CFL Twin tube 18W (4) Two triple tube 26W (4) 156 lx 179 lx 74 W 224 W $ 388 $ 552 White LEDs Mfr. A (6) 161 lx 168 W $ 2952 LED White LEDs Mfr. B (8) 167 lx 200 W $ 2384 White LEDs Mfr. C (8) 151 lx 120 W $

18 Lifecycle cost At the present time, in residential lighting, LED lighting costs more than incandescent or fluorescent lighting. In hospitality applications, the cost of using LED systems is approaching the cost of using traditional lighting systems. 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 Total Cost for 20yrs $7,000 $6,000 $5,000 $4,000 $3,000 $2,000 $1,000 $0 18 Inc 1 Inc 2 Inc 3 CFL 1 CFL 2 LED 1 LED 2 LED 3

19 Application considerations 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 19

20 Impact of heat on LEDs Heat negatively affects the performance of LEDs. Life (hrs) Light output Color Life (~ half the life for every 10 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 20

21 All products are not created the same Significant variation between products. Some LEDs have very short lifetime A, B, C, etc. are different 1W white LED products 100% 1W white LEDs High operated power white at LED 35 deg C, 350 ma Relative light output 95% 90% 85% 80% 75% F A D E B C 70% Time (hours) Narendran - LRC 21

22 Life of LEDs and LED systems Since heat shortens LED life (roughly half the life for every 10 C increase at the junction), system manufacturers have to provide sufficient heat sinking to ensure longer life. Additionally, installers have to make sure that they are not implementing LEDs into applications that increase the LED junction temperature. Performance of commercial LEDs varies significantly. Some good white LEDs have a lifetime in the range of 100,000 hrs plus, but there are many other products that have lifetimes as short as a few thousand hours. Presently, there are many commercial systems that may not have long life. Usually in the range of 10,000 hrs or less Buyers have to request life data from fixture manufacturers per ASSIST Recommends ( 22

23 MR16 replacement lamps Most LED products are advertised as direct replacements of MR16 halogen lamps 23

24 LED MR16 Lamps Workhorse of the industry - Halogen 50W MR16 ~ 750 lumens per lamp Most LED MR16s in the market have lumen values of 10 to 250 lumens. Cannot replace most halogen MR16s in lighting applications 750 lumens per lamp means too much heat within the fixture (2 diameter fixture) 24

25 Summary LEDs in directional lighting Some of the presently available LEDs can cater to directional lighting applications. LEDs perform much better in open-air operation Track lights, surface mount lights, etc LEDs will have much shorter life in recessed applications. Presently, LED systems cost higher than traditional lighting systems. They are becoming cost competitive in some commercial applications when considering lifecycle cost. With rapidly improving performance and decreasing cost of LEDs, these systems will become more cost effective in the next few years. 25

26 Street lighting applications

27 Street lighting with LEDs Increasing interest in using LEDs for street lighting. LED products for street lighting have been appearing on the Ann Arbor, MI LED streetlights test market continuously. New York City Lights Competition University of Abertay (Scotland) LED streetlights test Energy/LEDLighting.html Ede, Netherlands LED streetlights test

28 Example of LED in street lighting Comparison between typical high-pressure sodium (HPS) and LED 1000-ft 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 vs. 53-W LED IES distribution type III mounting height of 32-ft 2-ft setback and 4-ft arm length calculations consider initial values only (i.e., no lamp lumen depreciation) Type III distribution 4-ft 2-ft 32-ft 28

29 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. 29

30 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 LED fixture demanded much less power; at the same time the amount of light produced by the LED fixture was much less. Therefore, fixture C is not suitable for street lighting applications but may be suitable for some pathway lights 30

31 Product comparison - 2 Fixture A 150-W HPS semi cutoff cobra head Lumens per lamp Lumens per fixture Fixture power lm (150-W) lm (150-W) 189-W (150-W) Fixture D W white LEDs Lumens per fixture 11,200-lm Fixture power 188-W Mounting height = 20-ft Mounting height = 20-ft This LED system has performance similar to traditional HPS fixture. Therefore, more suited for street lighting applications. 31

32 Cost Outdoor fixtures 150 W MH ~$150 to $300 HPS ~$150 to $200 LED ~$700 to $1,500 32

33 Products compared Fixture A 150-W HPS semi cutoff cobra head Lumens per fixture Fixture power lm (150-W) 189-W (150-W) Fixture D W white LEDs Lumens per fixture 11,200-lm Fixture power 188-W Even though initial cost is high, lifecycle cost of LED systems could be lower due to reduced relamping and servicing. 33

34 Summary Rising number of LED street lighting products in the marketplace Many of them do not meet the lighting requirements However, a few products are starting to meet the requirements and compete with traditional light sources for area and street lighting applications. 34

35 Summary Already, LEDs can cater to certain illumination applications. Initial cost is much higher for LED fixtures LEDs are showing more promise when considering lifecycle cost In the next few years, white LED applications will ramp up rapidly. However, commercial LED products have significant variation in performance. Low quality, low performance products could hurt the entire industry. 35