Spatial Color Uniformity Research Articles

Simultaneously Improve White LED Omni-Directional Package Efficacy and Spatial Color Uniformity on Scattered Photon Extraction Technology

The Scattered Photon Extraction (SPE™) based on the concept of TIR lens combined with remote phosphor is proven to be one of the effective solutions for improving white LED efficiency, and it provides the omnidirectional light distribution for luminaire design. Not only the light extraction efficiency (LEE) is important, but also the angular uniformity of correlated color temperature (CCT) is a critical index in the evaluation of high-quality white LEDs. A non-optimized SPE™ will cause an increase in the angular CCT deviation (ACCTD) and ultimately affect lighting quality. Two possible ways using lens design are proposed to reduce the ACCTD and even improve its efficiency. Among them, using the concept of light guiding to design the lens can minimum the deviation of forward and backward CCT from 2720 K to 657 K, and the overall efficiency can be further enhanced by 12% compared to typical SPE™ lens.

Enhancement Spatial Color Uniformity of White Light LED Lamps by Adding Silicon Dioxides in Phosphor Layer

Recently, high-power light-emitting diodes (LEDs) have attracted great attention on the study and made remarkable progress. In this paper, method for enhancing uniform white light of a multi-chip white light LED by adding silicon dioxides in the phosphor layer is presented. Firstly, theory of study by using Mie theory and Monte Carlo ray-tracing is proposed. And then simulation and experimental results by using package LightTools software are performed. The experimental results and theory have the same direction: 1) the angular color temperature in narrow angles is much higher than that in wider angles for the non-SiO2 case and 2) in significantly reducing CCT deviation of a multi-chip white light LED by adding silicon dioxides in the phosphor layer. Keyword: Color uniformity, multi-chip white light LEDs, phosphor, silicon dioxide

Optimization of a merit function for the visual perception of color uniformity in spot lights

AbstractThe objective of the present study is the development of an optimized evaluation method which describes color uniformity in the far field of light‐emitting diode (LED) spot lights related to visual perception of color and pattern. The merit function is requested to evaluate measurements and optical simulations of spot light systems. A human factor experiment was performed as a two‐alternative forced choice (2AFC) test. During the experiment, a pairs of spot lights with various spatial color distributions were shown successively to the subject. The subjects had to select the more even spot light of the pair shown.The perceived rank order of spot lights was calculated afterwards. It was compared with five different mathematical functions describing several aspects of spatial color uniformity based on the CIELAB color space. These are the widely used color difference ΔE, gradient, difference of color average, circular symmetry description, and linear smoothness. No single basic function fits the perception in a sufficient way because none of the function considers all visual aspects. For a better correlation between the visual perception and the merit function, a linear combination of four basic functions is proposed. The designed merit function for the color uniformity of spot lights USL is more effective for the prediction of the visual perception. A correlation value of 0.91 is reached. It enables a quantitative evaluation of those LED lighting systems and protects against individual subjective judgments. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 287–296, 2015

Color selectivity of surface-plasmon holograms illuminated with white light

By using the optical frequency dependence of surface-plasmon polaritons, color images can be reconstructed from holograms illuminated with white light. We report details on the color selectivity of the color holograms. The selectivity is tuned by the thickness of a dielectric film covering a plasmonic metal film. When the dielectric is SiO(2) and the metal is silver, the appropriate thicknesses are 25 and 55 nm, respectively. In terms of spatial color uniformity, holograms made of silver-film corrugations are better than holograms recorded on photographic film on a flat silver surface.

Self-adaptive phosphor coating technology for wafer-level scale chip packaging

A new self-adaptive phosphor coating technology has been successfully developed, which adopted a slurry method combined with a self-exposure process. A phosphor suspension in the water-soluble photoresist was applied and exposed to LED blue light itself and developed to form a conformal phosphor coating with self-adaptability to the angular distribution of intensity of blue light and better-performing spatial color uniformity. The self-adaptive phosphor coating technology had been successfully adopted in the wafer surface to realize a wafer-level scale phosphor conformal coating. The first-stage experiments show satisfying results and give an adequate demonstration of the flexibility of self-adaptive coating technology on application of WLSCP.

Highly energy-efficient agricultural lighting by B+R LEDs with beam shaping using micro-lens diffuser

This paper presents a high-performance LED agricultural luminaire that uses a beam-shaping diffuser to achieve high optical efficiency and energy saving. The agricultural luminaire performs an optical efficiency as high as 84.2%. The beam shaping effect also obtains irradiance uniformity of 1/2.56 and excellent spatial color uniformity. The enhancement ratio of optical utilization factor in the proposed agricultural luminaire is 360% in comparison with traditional lighting. Under the designed case, the total utilization factor, including optical utilization factor and spectral utilization factor, of the B+R LED lamp can save 86.1% of power consumption in comparison with compact fluorescent bulbs.

Self-adaptive phosphor coating technology for white LED packaging

Phosphor-converted light-emitting diodes (pc-LEDs), which employ blue LEDs with yellow phosphors to generate white light illumination, is a widely used solidstate lighting source. In order to conduct a phosphor layer coating with high quality on LED chip, a self-adaptive coating technology is introduced in this paper. A slurry coating technique combined with self-exposure method is applied and developed to demonstrate the benefits of self-adaptive coating layer. For self-exposure, the slurry coating is exposed to the blue emission of LED itself other than to ultraviolet (UV) light outside to make photoresist crosslinking. Results of measurement indicate that white LEDs with self-adaptive coating have shown self-adaptability to the angular distribution of intensity of blue light and performed higher spatial color uniformity than those with conventional coating and other conformal coating.

Research on scattering properties of phosphor for high power white light emitting diode based on Mie scattering theory

Based on Mie scattering theory, the phosphor particle's scattering effect were simulated including light excitation and absorption. The light intensity proportion changes of forward and backward scattering light with different white light emitting diode (LED) color temperature were calculated. We also analyzed the phosphor particle size effecting the luminous flux of white LED and light color distribution of angle. Devices' excitation and emission spectrums used in our simulation were real measured spectrums of the material, rather than assuming a single spectrum. Our investigation discloses that when a conformal phosphor layer was adapted, phosphor particle diameter of 0.5 μm, makes maximum luminous flux and phosphor particles smaller, light color distribution of angel is better. While for given package structure, the best spatial color uniformity can be achieved with a phosphor layer thickness of 0.8 mm.

Near-ultraviolet LED of the External Quantum Efficiency Over 45% and its Application to High-color Rendering Phosphor Conversion White LEDs

Highly luminous efficiency and color rendering index (CRI) of 70 lm/W and 95 under low correlated color temperature (CCT) of 3177 K has been obtained by phosphor conversion (PC) white light-emitting diodes (LEDs) using near-ultra violet (n-UV) LEDs with the external quantum efficiency (EQE) of 46.7%. The homogeneous spatial color uniformity on chromaticity of PC white LEDs excited by n-UV LEDs are particularly adequate to the general lighting applications.

LP‐2: High Performance LCD Backlighting using High Intensity Red, Green and Blue Light Emitting Diodes

AbstractBy using red, green, and blue (RGB) light emitting diodes (LEDs) instead of cold cathode fluorescent lamps in edge lit LCD backlights brightness and color performance (gamut) of LCD displays can be improved considerably. However: the design of an RGB‐LED backlight and electronic control need special attention: the colors of the separate LEDs need to be mixed well to obtain a good spatial color uniformity while a good balance between the red, green and blue levels has to be maintained to stabilize the white point. Additional features of an RGB‐LED backlight solution are: dynamic white point control (tune color point of backlight to LCD and/or displayed material), large dimming range, long lifetime, ruggedness, and the absence of mercury.