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Testing Issues in LED Manufacturing

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Thermal Management for LED Applications

Part of the book series: Solid State Lighting Technology and Application Series ((SSLTA,volume 2))

Abstract

Power to a light-emitting diode (LED) is converted to light and heat. However, these are not independent and affect each other in complex ways. Knowing the thermal state of the LED chip is essential to understanding the light output properties of the LEDs. Controlling the temperature of thermal contacts is used in the testing of LEDs, where possible. Changes to some LED optical and electrical properties with temperature are described with examples.

The setups used in testing LEDs for total flux and averaged LED intensity are discussed with practical equipment illustrations. The configurations and conditions for laboratory and production lines are compared. The relationships are explored so that the correction of production test results to laboratory quantities can be made.

The effects of measurement equipment on the results are examined; in particular, the requirements of nonequilibrium testing with short pulses. Short pulses are routinely employed in production testing and results “corrected” to equilibrium conditions.

The role of uncertainties and tolerances and their differences are discussed. Measurement precision, result distribution, and their relationship to actions such as rejection and binning protocols are explored. In particular, the effect of traceability paths on the observed differences between production lines is explained. Comparison of results depends on the number of variables involved in tests and the scope of the intercomparison.

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Notes

  1. 1.

    One needs to make the distinction between two kinds of efficacy. ILV, the International Lighting Vocabulary published by CIE [1] defines two terms. The one used to compare electric light sources (term 17-729 of ILV) is the usual (luminous) efficacy of light source defined as the ratio of the emitted luminous flux and the input electrical power. Throughout this chapter, the word efficacy refers to this quantity. The second type of efficacy is called (luminous) efficacy of source of radiation (term 17-730 of ILV) defined as the ratio of the emitted luminous flux and the emitted radiant flux. Both quantities are measured in lm/W. The third term related to efficiency to characterize LEDs is called radiant efficiency (term 17-1018 of ILV) defined as emitted radiant power divided by the supplied input electric power. See also the JEDEC JESD51-53 [2] document for some of these definitions.

  2. 2.

    Chapter 4 on thermal testing and Chap. 6 on standardization provided definitions of LED temperature. These definitions are based on repeatability considerations of measurements. In daily practice, convenience of LED users is the major factor which determines how LED vendors define thermal reference points for their products.

  3. 3.

    Usually, the purpose of measuring exactly the case temperature is to determine the R thJC junction-to-case thermal resistance.

  4. 4.

    In testing standards of light sources and luminaries.

  5. 5.

    For a physically sound definition of thermal resistance between two locations along a heat-flow path refer to Sect. 6.1.4 of Chap. 6.

  6. 6.

    One should wait with starting the optical measurement at least as much after the electrical switching or temperature change as the thermal time-constant of the system containing the test LED, see, e.g., the timing diagram shown in Fig. 6.20 of Chap. 6.

  7. 7.

    According to the JEDEC LED thermal testing standards (JESD51-51 [3] and JESD 51-52 [4]), the temperature of the LED under test has to be controlled. For details refer to Chap. 4 and Chap. 6.

  8. 8.

    In case of forward emitting LEDs attached to a cold plate at the side of an integrating sphere it is sufficient to control the cold plate temperature which in such a setup is used as reference temperature. This is the requirement of the JEDEC JESD51-52 standard [4].

  9. 9.

    See Sect. 5.1.2 and Eq. 5.9 in Chap. 5.

  10. 10.

    Note: this is not the “Partial LED flux” quantity defined by CIE, but is instead a simple expression that not all the flux is measured.

  11. 11.

    The spectral distribution of the sensitivity of human eye under photopic conditions is described by the V(λ) function—see also Chap. 5.

  12. 12.

    See the definition of luminous flux in Chap. 5.

References

  1. CIE S 017/E:2011 ILV: International lighting vocabulary

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  2. JEDEC Standard JESD51-53 (2012) Terms, definitions and units glossary for LED thermal testing. http://www.jedec.org/sites/default/files/docs/jesd51-53.pdf

  3. JEDEC Standard JESD51-51 (2012) Implementation of the electrical test method for the measurement of the real thermal resistance and impedance of light-emitting diodes with exposed cooling surface. www.jedec.org/sites/default/files/docs/JESD51-51.pdf

  4. JEDEC Standard JESD51-52 (2012) Guidelines for combining CIE 127-2007 Total flux measurements with thermal measurements of LEDs with exposed cooling surface. www.jedec.org/sites/default/files/docs/JESD51-52.pdf

  5. Zong Y, Ohno Y (2008) New practical method for measurement of high-power LEDs, Proceedings of CIE Expert Symposium 2008, July 2008, Turin, Italy, CIE x033:2008, 1002-106

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  10. ENERGY STAR® (2010) Program requirements for integral LED lamps, eligibility criteria—version 1.1, amended—March 22. Energy Star® website. http://www.energystar.gov/

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Author information

Authors and Affiliations

  1. Instrument Systems GmbH, Munich, Germany

    Richard Young PhD

Authors
  1. Richard Young PhD
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Correspondence to Richard Young PhD .

Editor information

Editors and Affiliations

  1. Philips Research Emeritus, Nuenen, The Netherlands

    Clemens J.M. Lasance

  2. MicReD Unit Budapest XI, Infopark D, Mentor Graphics Mechanical Analysis Divi, Budapest XI, Infopark D, Hungary

    András Poppe

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Young, R. (2014). Testing Issues in LED Manufacturing. In: Lasance, C., Poppe, A. (eds) Thermal Management for LED Applications. Solid State Lighting Technology and Application Series, vol 2. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-5091-7_11

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  • DOI: https://doi.org/10.1007/978-1-4614-5091-7_11

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  • Publisher Name: Springer, New York, NY

  • Print ISBN: 978-1-4614-5090-0

  • Online ISBN: 978-1-4614-5091-7

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