Are current photometric tests for incandescent lights valid for LEDs?

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1 ANNUAL IES AVIATION LIGHTING COMMITTEE FALL CONFERENCE 2014 CORONADO SPRINGS RESORT, ORLANDO, FLORIDA OCTOBER 19-24, 2014 Are current photometric tests for incandescent lights valid for LEDs? Jean Paul Freyssinier, Yiting Zhu, and N. Narendran Lighting Research Center, Rensselaer Polytechnic Institute Project Sponsor: Federal Aviation Administration Cooperative Agreements Number: FAA/05-C-AT-RPI, 10-G-013 and 13-G-009 1

2 LRC and Aviation Lighting Research 2

3 Background LED aviation signal lights are being increasingly considered for airfield lighting applications. Photometric tests of LED based systems are conducted using existing test procedures that were developed for incandescent lamp based systems. But, are these photometric test methods appropriate for LED as well? Funded by the Federal Aviation Administration the Lighting Research Center (LRC) reviewed several Advisory Circulars and have proposed several recommendations for changes when testing LED systems. These changes were mainly in three sections: life testing, test temperatures and temperature measurement points, and photometric test procedures.

4 Short-term effect of heat at the junction Peak wavelength shifts with changes in junction temperature Relative Output Red LED Wavelength (nm) 20 ma 30 ma 40 ma 50 ma 60 ma 70 ma Peak Wavelength (nm) Peak Wavelength (nm) y = x y = x y = x y = x y = x Junction Temperature (Celsius) 5 mm Blue LED Junction Temperature (deg ma 25 deg C 40 deg C 70 deg C 4

5 Short-term effect of heat at the junction Light output decreases with increasing temperature Different types of LEDs have different temperature sensitivity Red ~ 0.8 % per o C Green ~ 0.3 % per o C Blue ~ 0.06 % per o C courtesy of Lumileds 5

6 Long-term effect of heat at the junction Light output High Power White 100% 90% 80% 70% 60% 50% Hours 63 deg C 74 deg C Junction temperature effects L 70 from 38,000 hrs to 14,000 hrs L 50 from 62,000 hrs to 24,000 hrs Sponsor: U.S. DOE, UCSB DOE Grant DE-FC26-01NT

7 Background: Scope of Work Task 1: Review of FAA Advisory Circulars to understand lighting and system performance requirements how testing procedures relate to LED systems Task 2: Conduct laboratory tests of existing LED fixtures to develop and verify appropriate metrics and methodologies methodology should cover colored and white airport lighting luminaires for all light source technologies

8 Background: Task 1 Relevant Advisory Circulars reviewed EB 67 SAE / / F 150/5210-5B 150/ C 150/ B 150/ A 150/ A 150/ C 150/ / A 150/ C Relevant topics within Advisory Circulars General specifications, life, photometric, thermal, and electrical requirements Overlap between test methods for general lighting fixtures and airport fixtures

9 Topics for Investigation Effects of temperature ambient temperature definition and recommendations for sensor location test temperature range warm-up time Location of temperature sensor of arctic kit Definition of life and life-test methods Dimming methods and associated issues Seasoning

10 Where to measure LED temperature? Tj cannot be measured directly Ts (or Tb or Tpin) is related to Tj and can be measured using a thermal sensor VioDataSheetWEB8_7_07.pdf pdf/xlamp7090xr-e.pdf epage 10

11 Effects of Temperature: Test Range FAA specification requirements: Perform tests at -40 ºC and +55 ºC. Measured peak wavelength shift over the range 25 to 55 ºC L-810 Red Obstruction Light y CIE 1931 chromaticity diagram Chromaticity at 25ºC Chromaticity at 25ºC Chromaticity at 55ºC 0.33 Chromaticity at 55ºC 0.33 yellow boundary yellow boundary purple boundary purple boundary Efficiency implications x Peak wavelength shift (nm) LED Peak Wavelength Shift with Pin Temperature L-810 red obstruction light ºC ambient 42.1 ºC pin (640 nm) Peak wavelength 55 ºC ambient 66.9 ºC pin (645 nm) Time (min)

12 Effects of Temperature: Warm-up Time Sample A2 - Tb = 80 C WHITE and RED LEDs 120 C 100 C Stabilization time of LED systems can take several hours LED board or driver temperature 80 C 60 C 40 C 20 C 0 C -24 h -22 h -20 h -18 h -16 h -14 h -12 h -10 h -8 h -6 h -4 h Time (h) Photometric and electrical characteristics depend on the junction temperature (Tj) LED relative light output Sample A2 - Tb = 80 C WHITE and RED LEDs 106.0% 105.0% 104.0% 103.0% 102.0% 101.0% 100.0% 99.0% 98.0% 97.0% -24 h -22 h -20 h -18 h -16 h -14 h -12 h -10 h -8 h -6 h -4 h Time (h)

13 Stabilization of SSL Products (according to IES LM-79) 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 % 13

14 Test of an SSL Downlight Product Input Power (W) Relative Light Output Input Power Light Output Time (min) 14

15 Test of an SSL Downlight Product % 12.5 Input Power (W) Efficacy by 2.3% Over next 12 hours 0.9% Relative Light Output Input Power Light Output Time (min) 15

16 Effects of Temperature: Accelerated life test Presently, the accelerated life test calls for a 20-h on and 4-h off cycle Stabilization time of LED systems can take several hours Temperature 140 C 120 C 100 C 80 C 60 C 40 C 20 C Sample A5 - Tb = 100 C 12-h ON, 12-h OFF 24 h 48 h 72 h 96 h 120 h Time (h) Ambient Driver LED

17 Conclusions Existing specifications and test procedures do not cover all the potential problems with LED products. Different LED technologies can present various challenges that need to be addressed. Ongoing research is addressing the definition of life and a methodology for testing.

18 Acknowledgments Federal Aviation Administration Funding through Cooperative Agreement FAA/05-C-AT-RPI, 10-G-013 FAA Program Manager, COE for Airport Technology Research: David Brill, Ph.D. Don Gallagher served as technical monitor LRC faculty, staff, and students Lalith Jayasinghe, Yimin Gu, Andrew Bierman, Yiting Zhu, Yi-wei Liu, Terry Klein, Martin Overington, Howard Ohlhous 18

19 Seasoning of SSL Products (according to IES LM-79) 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 19