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Polarized white light from LEDs using remote-phosphor layer sandwiched between reflective polarizer and light-recycling dichroic filter

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Abstract

This study introduces an efficient polarized, white phosphor-converted, light-emitting diode (pc-LED) using a remote phosphor film sandwiched between a reflective polarizer film (RPF) and a short-wavelength pass dichroic filter (SPDF). The on-axis brightness of polarized white light emission of a RPF/SPDF-sandwiched phosphor film over a blue LED, showed greater recovery than that of a conventional unpolarized remote phosphor film over blue LED, due to the recycling effect of yellow light from an SPDF. The relative luminous efficacy of an RPF/SPDF-sandwiched phosphor film was made 1.40 times better by adding an SPDF on the backside of an RPF-capped phosphor film. A polarization ratio of 0.84 was demonstrated for a white LED with an RPF/SPDF-sandwiched phosphor film, in good agreement with the measured results from the RPF-only sample.

©2013 Optical Society of America

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Figures (8)

Fig. 1
Fig. 1 Schematic diagrams of (a) an actual lighting fixture featuring remote-phosphor, and (b) the RPF/SPDF-sandwiched remote-phosphor.
Fig. 2
Fig. 2 Transmittance spectra of SPDF (blue line) and RPF (red line) (Black line spectrum; the normalized emission spectrum of a yellow phosphor film on a blue LED).
Fig. 3
Fig. 3 Schematic diagrams and photographs of four pc-LED configurations with differently designed remote-phosphor layers (a) conventional, (b) RPF-capped, (c) SPDF-inserted, and (d) RPF/SPDF-sandwiched remote-phosphor layer. (The arrow with a two-sided arrow indicates p-polarization light, an arrow with a dot indicates s-polarization light, and both (a two-sided arrow and dot) indicate unpolarized light.)
Fig. 4
Fig. 4 The EL spectra of four different types of remote phosphor films on blue LED: (a) conventional and SPDF-inserted and (b) RPF-capped and RPF/SPDF-sandwiched phosphor layer.
Fig. 5
Fig. 5 Four different types of remote phosphor films on blue LEDs: conventional, RPF-capped, SPDF-inserted, and RPF/SPDF-sandwiched phosphor layer (a) the relative luminous flux, (b) the conversion efficiency, (c) the CIE color coordinates, and (d) the correlated color temperature (CCT).
Fig. 6
Fig. 6 The CCT distribution of four samples (conventional, RPF-capped, SPDF-inserted, and RPF/SPDF-sandwiched, remote phosphor white LED) as a function of viewing angle.
Fig. 7
Fig. 7 (a) Schematic diagram of the polarizer-rotating measurement system, and (b) the relative yellow intensity (at 565nm) of four different types of remote phosphor films on blue LEDs: conventional, RPF-capped, SPDF-inserted, and RPF/SPDF-sandwiched phosphor layer.
Fig. 8
Fig. 8 EL spectra of cases with and without polarizer (a) RPF-capped, and (b) RPF/SPDF-sandwiched phosphor layer.
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