Abstract

White light emitting diode (LED) systems, capable of lowering the color temperature of emitted light on dimming, have been reported in the literature. These systems all use multiple color LEDs and complex control circuitry. Here we present a novel responsive lighting system based on a single white light emitting LED and a thermoresponsive scattering coating. The coated LED automatically emits light of lower correlated color temperature (CCT) when the power is reduced. We also present results on the use of multiple phosphors in the white light LED allowing for the emission of warm white light in the range between 2900 K and 4150 K, and with a chromaticity complying with the ANSI standards (C78.377). This responsive warm white light LED-system with close-to-ideal emission characteristics is highly interesting for the lighting industry.

© 2014 Optical Society of America

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References

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  1. N. Zheludev, “The life and times of the LED – a 100-year history,” Nat. Photonics 1(4), 189–192 (2007).
    [Crossref]
  2. M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
    [Crossref]
  3. S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
    [Crossref]
  4. E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
    [Crossref] [PubMed]
  5. P. R. Rahm and W. R. McGrath, “Apparatus and method for adjusting the color temperature of white semiconduct or light emitters,” US patent No. 6636003 B2, 2003.
  6. Y. Okumura, “Color temperature-regulable led light,” European Patent No. EP1462711 A1, 2004.
  7. P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
    [Crossref]
  8. L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
    [Crossref]
  9. T. van Bommel and R. A. M. Hikmet, “Lighting device with thermally variable reflecting element,” US patent No. 8432500 B2, 2013.
  10. G. W. Gray, Fundamentals, Vol. 1 of Handbook of Liquid Crystals (Wiley-VCH, 1998).
  11. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, 2008).
  12. C. Tschierske, “Non-conventional liquid crystals-the importance of micro-segregation for self-organisation,” J. Mater. Chem. 8(7), 1485–1508 (1998).
    [Crossref]
  13. M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
    [Crossref]
  14. J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
    [Crossref]
  15. H.-H. Moretto, M. Schulze, and G. Wagner, Silicones, Vol. 32 of Ullmann’s Encyclopedia of Industrial Chemistry (Wiley-VCH, 2000).
  16. X. Fu and X. Luo, “Can thermocouple measure surface temperature of LED module accurately?” Int. J. Heat Mass Transfer 65, 199–202 (2013).
    [Crossref]
  17. W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
    [Crossref]
  18. F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
    [Crossref]
  19. Specifications for the Chromaticity of Solid State Lighting Products, ANSI Standard ANSLG C78.377−2011.
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    [Crossref]
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    [Crossref]
  22. B. Marciniec and J. Matisons, Hydrosilylation: A Comprehensive Review on Recent Advances, Vol. 1 of Advances in Silicon Science (Springer, 2009).

2013 (1)

X. Fu and X. Luo, “Can thermocouple measure surface temperature of LED module accurately?” Int. J. Heat Mass Transfer 65, 199–202 (2013).
[Crossref]

2012 (1)

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

2011 (1)

P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
[Crossref]

2010 (1)

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

2009 (2)

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

2007 (1)

N. Zheludev, “The life and times of the LED – a 100-year history,” Nat. Photonics 1(4), 189–192 (2007).
[Crossref]

2006 (1)

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

2005 (1)

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[Crossref] [PubMed]

2004 (2)

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

1998 (2)

C. Tschierske, “Non-conventional liquid crystals-the importance of micro-segregation for self-organisation,” J. Mater. Chem. 8(7), 1485–1508 (1998).
[Crossref]

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

1942 (1)

Alger, J. S.

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

Bahadur, M.

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

Beattie, H. N.

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

Chang, M.-H.

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

Chen, L.

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

Clapp, T. V.

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

Das, D.

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

DeGroot, J. V.

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

DenBaars, S. P.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

Draheim, J.

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

Fu, X.

X. Fu and X. Luo, “Can thermocouple measure surface temperature of LED module accurately?” Int. J. Heat Mass Transfer 65, 199–202 (2013).
[Crossref]

Glover, S. O.

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

Hwang, W. J.

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

Kamberger, R.

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

Kim, J. K.

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[Crossref] [PubMed]

Kim, L.

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

Lacey, D.

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

Lee, T. H.

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

Lin, C.-C.

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

Liu, R.-S.

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

Luo, X.

X. Fu and X. Luo, “Can thermocouple measure surface temperature of LED module accurately?” Int. J. Heat Mass Transfer 65, 199–202 (2013).
[Crossref]

MacAdam, D. L.

Mitchell, G. R.

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

Nakamura, S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

Norris, A.

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

Norris, A. W.

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

Parmentier, A. B.

P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
[Crossref]

Pecht, M.

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

Pimputkar, S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

Poelman, D.

P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
[Crossref]

Pople, J. A.

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

Schneider, F.

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

Schubert, E. F.

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[Crossref] [PubMed]

Shin, M. W.

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

Smet, P. F.

P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
[Crossref]

Speck, J. S.

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

Tschierske, C.

C. Tschierske, “Non-conventional liquid crystals-the importance of micro-segregation for self-organisation,” J. Mater. Chem. 8(7), 1485–1508 (1998).
[Crossref]

Varde, P. V.

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

Wallrabe, U.

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

Windiate, C. C.

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

Yeh, C.-W.

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

Zarisfi, A.

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

Zheludev, N.

N. Zheludev, “The life and times of the LED – a 100-year history,” Nat. Photonics 1(4), 189–192 (2007).
[Crossref]

Int. J. Heat Mass Transfer (1)

X. Fu and X. Luo, “Can thermocouple measure surface temperature of LED module accurately?” Int. J. Heat Mass Transfer 65, 199–202 (2013).
[Crossref]

J. Electrochem. Soc. (1)

P. F. Smet, A. B. Parmentier, and D. Poelman, “Selecting conversion phosphors for white light-emitting diodes,” J. Electrochem. Soc. 158(6), R37–R54 (2011).
[Crossref]

J. Mater. Chem. (2)

C. Tschierske, “Non-conventional liquid crystals-the importance of micro-segregation for self-organisation,” J. Mater. Chem. 8(7), 1485–1508 (1998).
[Crossref]

D. Lacey, H. N. Beattie, G. R. Mitchell, and J. A. Pople, “Orientation effects in monodomain nematic liquid crystalline polysiloxane elastomers,” J. Mater. Chem. 8(1), 53–60 (1998).
[Crossref]

J. Opt. Soc. Am. (1)

Materials (1)

L. Chen, C.-C. Lin, C.-W. Yeh, and R.-S. Liu, “Light converting inorganic phosphors for white light-emitting diodes,” Materials 3(3), 2172–2195 (2010).
[Crossref]

Microelectron. Reliab. (1)

M.-H. Chang, D. Das, P. V. Varde, and M. Pecht, “Light emitting diodes reliability review,” Microelectron. Reliab. 52(5), 762–782 (2012).
[Crossref]

Nat. Photonics (2)

S. Pimputkar, J. S. Speck, S. P. DenBaars, and S. Nakamura, “Prospects for LED lighting,” Nat. Photonics 3(4), 180–182 (2009).
[Crossref]

N. Zheludev, “The life and times of the LED – a 100-year history,” Nat. Photonics 1(4), 189–192 (2007).
[Crossref]

Phys. Stat. Solidi C (1)

W. J. Hwang, T. H. Lee, L. Kim, and M. W. Shin, “Determination of junction temperature and thermal resistance in the GaN-based LEDs using direct temperature measurement,” Phys. Stat. Solidi C 1(10), 2429–2432 (2004).
[Crossref]

Proc. SPIE (2)

M. Bahadur, A. W. Norris, A. Zarisfi, J. S. Alger, and C. C. Windiate, “Silicone materials for LED packaging,” Proc. SPIE 6337, 63370F (2006).
[Crossref]

J. V. DeGroot, A. Norris, S. O. Glover, and T. V. Clapp, “Highly transparent silicone materials,” Proc. SPIE 5517, 116–123 (2004).
[Crossref]

Science (1)

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[Crossref] [PubMed]

Sens. Actuators A Phys. (1)

F. Schneider, J. Draheim, R. Kamberger, and U. Wallrabe, “Process and material properties of polydimethylsiloxane (PDMS) for optical MEMS,” Sens. Actuators A Phys. 151(2), 95–99 (2009).
[Crossref]

Other (8)

Specifications for the Chromaticity of Solid State Lighting Products, ANSI Standard ANSLG C78.377−2011.

H.-H. Moretto, M. Schulze, and G. Wagner, Silicones, Vol. 32 of Ullmann’s Encyclopedia of Industrial Chemistry (Wiley-VCH, 2000).

P. R. Rahm and W. R. McGrath, “Apparatus and method for adjusting the color temperature of white semiconduct or light emitters,” US patent No. 6636003 B2, 2003.

Y. Okumura, “Color temperature-regulable led light,” European Patent No. EP1462711 A1, 2004.

T. van Bommel and R. A. M. Hikmet, “Lighting device with thermally variable reflecting element,” US patent No. 8432500 B2, 2013.

G. W. Gray, Fundamentals, Vol. 1 of Handbook of Liquid Crystals (Wiley-VCH, 1998).

P. G. de Gennes and J. Prost, The Physics of Liquid Crystals (Clarendon, 2008).

B. Marciniec and J. Matisons, Hydrosilylation: A Comprehensive Review on Recent Advances, Vol. 1 of Advances in Silicon Science (Springer, 2009).

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Figures (12)

Fig. 1
Fig. 1

Schematic depiction of the LED-package with the thermo-responsive coating on top. The picture on the left shows the device at low temperature/current, where the coating is in a scattering state. In the picture on the right the current/temperature is high and the coating is thus transparent. The color of the coating in this schematic depiction shows the color of the light leaving the device. For the sake of clarity the coating is depicted out of contact with the LED package; it should be noted, however, that the coating is brought into optical and thermal contact with the LED package.

Fig. 2
Fig. 2

a) Correlated color temperature (CCT) of the light emitted by the LED at different currents and temperatures applied to a cold white light LED coated with the thermo-responsive coating. The black diamond symbols show the uncoated LEDs. The red squares display the first run of increasing (closed symbols) and decreasing (open symbols) the current. The red circles display the second run. b) Demonstrator consisting of a row of coated cold white LEDs on the left-hand side and a row of bare cold white LEDs on the right-hand side. The top picture shows the demonstrator operating at a low current (~20 mA/LED) and the bottom picture at a high current (~60 mA/LED). In order to capture the switching of CCT on camera a diffuser is placed on top of the demonstrator at a large distance (approximately 5 cm).

Fig. 3
Fig. 3

The CIE 1931 diagram depicting the chromaticities of the light emitted by an uncoated cold white light LED (black data points) and a coated cold white light LED (blue data points), measured at different currents (5-60 mA). The right figure is an expansion of the relevant part of the left figure. The purple line represents the connection between the value in color space of the blue LED and the phosphor in question. The black curve represents the ideal black body emitter. The ellipses depict 5-steps MacAdam ellipses around black body emitters at a certain temperature.

Fig. 4
Fig. 4

Absorption (dashed lines) and emission (solid lines) spectra of the yellow (green lines) and the red phosphor (red lines) and the blue LED (blue line) present in a warm white light LED.

Fig. 5
Fig. 5

a) Correlated color temperature (CCT) of the light emitted by the LEDs at different currents and temperatures. The black symbols display the uncoated LED and the red symbols the coated LED. The red squares depict the first run of increasing (closed symbols) and decreasing (open symbols) the current. The circles display the second run. b) Demonstrator consisting of a row of coated warm white LEDs (bottom) and a row of bare warm white LEDs (top). The top picture shows the demonstrator operating at a low current (~20 mA/LED) and the bottom picture at a high current (~80 mA/LED). In order to capture the switching of CCT on camera a diffuser is placed on top of the demonstrator at a large distance (approximately 5 cm).

Fig. 6
Fig. 6

CIE 1931 diagram depicting the chromaticities of the light emitted by an uncoated (black) and a coated LED (blue), measured at different currents (5-90 mA). The right figure is an expansion of the relevant part of the left figure. The red and yellow lines represent the connections between the chromaticity of the blue LED and the two different phosphors. The black curve represents the ideal black body emitter. The ellipses depict 5-steps MacAdam ellipses around black body emitters at a certain temperature. Several CCT lines are shown as black dotted lines.

Fig. 7
Fig. 7

Synthesis of 6-(4-((4-methoxyphenoxy)carbonyl)phenoxy)hexyl-methylsiloxane dimethylsiloxane copolymer (compound 3).

Fig. 8
Fig. 8

The DSC and POM investigation of the phase behavior of compound 3.

Fig. 9
Fig. 9

The WAXS (left) and SAXS (right) images for the a) higher-temperature smectic phase and b) lower-temperature smectic phase (see Fig. 8).

Fig. 10
Fig. 10

SEM images of the thermoresponsive coating at different magnifications: a) 700x, b) 13000x, c) 50000x.

Fig. 11
Fig. 11

Surface temperature of the LED as function of the applied current.

Fig. 12
Fig. 12

CIE 1931 diagram depicting the chromaticities of the light emitted by various samples of coated warm white LEDs measured at different electrical currents (5-60 mA). The data points shown in different colors were obtained by polymerization at different temperatures. All coatings contained 50% of compound 3. The black curve represents the ideal black body emitter. The ellipses depict 5-steps MacAdam ellipses around black body emitters at a certain temperature. Several CCT lines are shown as black dotted lines.

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