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New paradigm of multi-chip white LEDs: combination of an InGaN blue LED and full down-converted phosphor-converted LEDs

Ji Hye Oh, Jeong Rok Oh, Hoo Keun Park, Yeon-Goog Sung, and Young Rag Do

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Abstract

This study introduces innovative multi-chip white LED systems that combine an InGaN blue LED and green/red or green/amber/red full down-converted, phosphor-conversion LEDs (pc-LEDs). Efficient green, amber, and red full down-converted pc-LEDs were fabricated by simply capping a long-wave pass filter (LWPF) on top of LED packing associated with each corresponding powder phosphor. The principal advantage of this type of color-mixing approach in newly developed multi-chip white LEDs based on colored pc-LEDs is thought to be dynamic control of the chromaticity and better light quality. In addition, the color-mixing approach improves the low efficacy of green/amber LEDs in the “green gap” wavelength; reduces the wide color/efficacy variations of each primary LED with at different temperatures and currents; and improves the low color rendering indexes of the traditional color-mixing approach in red, green, and blue (RGB) multi-chip white LEDs.

©2011 Optical Society of America

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Figures (7)
Fig. 1
Fig. 1 Schematic diagrams of the color-mixing approaches to generate white light from single-chip and multi-chip LEDs. (a) white-by-blue (YBB or RBGBB) or white-by-violet (RUVGUVBUV) phosphor-converted single chip white LED. (b) AlGaInP red, InGaN green and blue (RGB) multi-chip white LED. (c) white LED package with UV, blue, violet multi-chip LEDs, green/red phosphors, and an ODR filter, (d) full conversion pc-LED red, green, and InGaN blue (RB,MGB,MB) multi-chip white LED. (e) full conversion pc-LED red, amber, green, and InGaN blue (RB,MAB,MGB,MB) multi-chip white LED. (f) Schematic diagram of the mechanism of the blocking and recycling of the forward unabsorbed emission of a blue LED by capped-LWPF into the phosphor-coated LED die.

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Fig. 2
Fig. 2 The overlapped emission spectra of each LED in four different white-light systems; (a) RGB, (b) RAGB, (C) RB,MGB,MB, (d) RB,MAB,MGB,MB multi-chip white LED. The inset shows the color diagram of the CIE (CIE = Commission Internationale d’Eclairage) of each white-light system.

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Fig. 3
Fig. 3 The luminous efficacy of a full down-converted monochromatic pc-LED and a direct-emitting monochromatic semiconductor LED without phosphors as a function of the applied current; (a) green color, (b) amber color, and (c) red color. The normalized luminous efficacy of both pc-LEDs and III-V LEDs as a function of the ambient temperature; (d) green color, (e) amber color, and (f) red color.

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Fig. 4
Fig. 4 The variations of the CIE color coordinates of a full down-converted monochromatic pc-LED and a direct-emitting monochromatic semiconductor LED without phosphors as a function of the applied current; (a) green color, (b) amber color, and (c) red color and as a function of the ambient temperature; (d) green color, (e) amber color, and (f) red color. Arrows indicate increase of the applied current from 0.5mA to 300mA; (a),(b),(c), and the ambient temperature from 20°C to 120°C; (d), (e), (f).

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Fig. 5
Fig. 5 The emitted spectrum distribution of (a) RGB, (b) RAGB, (C) RB,MGB,MB, (d) RB,MAB,MGB,MB multi-chip white clusters for a set of eight CCTs specified in the ANSI standard.

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Fig. 6
Fig. 6 The fractional applied currents of the primary LEDs in four different multi-chip white LED sets as a function of the CCT; (a) RGB, (b) RAGB, (C) RB,MGB,MB, and (d) RB,MAB,MGB,MB multi-chip white LED.

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Fig. 7
Fig. 7 The luminous efficacy, relative quantum efficiency, relative brightness, and CRIs (Ra) of four different (RGB, RAGB, RB,MGB,MB, and RB,MAB,MGB,MB) clusters of multi-chip white LEDs as functions of the CCT. The relative quantum efficiency and relative brightness were compared with the emission spectrum of a blue InGaN LED.

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