Abstract
In this study, a simple and low-cost method is proposed to enhance angular color uniformity (ACU) of color-mixed light-emitting diodes (cm-LEDs) by introducing a diffuse coating layer. Optical models of the proposed cm-LEDs packaging modules were constructed by Monte Carlo ray-tracing simulation. The simulation results demonstrate the ACU enhancement of the cm-LEDs packaging modules with the application of the diffuse coating layer on the reflection cup. Owing to the strong light scattering and diffuse reflection effects of the diffuse coating layer, the different color light emitted from the different chip are sufficiently mixed. The diffuse coating layer was fabricated by spraying method. Its optical performance was demonstrated by experiments. The correlated color temperature (CCT) deviations of the cm-LEDs applying the diffuse coating layer have been reduced from 1174 K to 138 K at viewing angles ranging from -80° to +80°. A lowest luminous flux loss of 3.54% is obtained. The diffuse coating layer could also maintain the excellent ACU performance when the average CCTs changes from about 2000 K to 5200 K. Extremely small CCT deviations were obtained, which are less than 300 K at average CCTs ranging from 2000 K to 5200 K. The results demonstrate that the diffuse coating layer on reflection cup is a feasible and effective method to enhance the ACU of the cm-LEDs.
Highlights
Due to advantages over traditional light sources in terms of efficiency, life time, reliability and environmental protection, white light-emitting diodes (LEDs) have widely penetrated into many illumination applications, such as backlighting, street lighting, headlamp and interior illumination [1]–[3]
The correlated color temperature (CCT) deviations of the color-mixed light-emitting diodes (cm-LEDs) applying the diffuse coating layer have been reduced from 1174 K to 138 K at viewing angles ranging from −80° to +80°
Optical models of the proposed cm-LEDs packaging modules were presented by Monte Carlo ray-tracing simulation to study the effect of the diffuse coating layer on the angular color uniformity (ACU) performance of cm-LED packaging modules
Summary
Due to advantages over traditional light sources in terms of efficiency, life time, reliability and environmental protection, white light-emitting diodes (LEDs) have widely penetrated into many illumination applications, such as backlighting, street lighting, headlamp and interior illumination [1]–[3]. Changing the morphology of the phosphor layer by different processing methods to make optical path of blue light consistent at all viewing angles is an effective way to realize the ACU improvement [9]–[11]. Adding nano/micro particles in the phosphor layer to enhance light scattering is a simple method to improve ACU [12]–[14]. To provide a uniform color distribution for cm-LEDs, many different optical elements are used, including diffractive structures, light guides, lenses, prisms, and optical diffusers [15]–[17]. Microlens arrays (MLAs) fabricated on surface of encapsulation layer is an effective scattering structure to improve color mixing. We propose to realize ACU improvement of cm-LEDs through fabricating a diffuse coating layer on reflector cup by a simple spraying method. The cm-LEDs modules were packaged by the reflector cup with diffuse coating layer and their optical performances were investigated in detail
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