Design of a novel freeform lens for LED uniform illumination and conformal phosphor coating

Abstract

A conformal phosphor coating can realize a phosphor layer with uniform thickness, which could enhance the angular color uniformity (ACU) of light-emitting diode (LED) packaging. In this study, a novel freeform lens was designed for simultaneous realization of LED uniform illumination and conformal phosphor coating. The detailed algorithm of the design method, which involves an extended light source and double refractions, was presented. The packaging configuration of the LED modules and the modeling of the light-conversion process were also presented. Monte Carlo ray-tracing simulations were conducted to validate the design method by comparisons with a conventional freeform lens. It is demonstrated that for the LED module with the present freeform lens, the illumination uniformity and ACU was 0.89 and 0.9283, respectively. The present freeform lens can realize equivalent illumination uniformity, but the angular color uniformity can be enhanced by 282.3% when compared with the conventional freeform lens.

Adding an extra condition: a general method to design double freeform-surface lens for LED uniform illumination

“…To evaluate the illumination uniformity, the variation coefficient of root mean square error, or CV(RMSE) in short, was calculated. It is defined as [16][17][18][19] …”

“…The flat inner surface can realize uniform thickness of phosphor layer, and then we designed the outer surface to achieve uniform illumination by controlling the direction of the emergent ray from the preset inner surface. The detailed design process and validation can be referred to our previous study [17]. …”

Robustness of point light source approximation in lens design for light-emitting diode packages

“…The lens design methods of RSL, NRSL and TIRL have been studied and reported extensively. Our group also conducts a lot of studies about lens design mainly based on controlling the light energy mapping relationship and the light pattern [5][6][7][8]. When the light pattern is rotationally symmetrical, then RSL is designed; when the light pattern is rectangular, then NRSL is designed; when multiple freeform surfaces are designed simultaneously with both refraction and reflection coupled, then TIRL is designed.…”

“…Since the dimensions of LED chips are very small, the LED chip is usually considered as point light source, which make the lens design convenient and efficient. Based on the point light source approximation, there are several methods referring to the lens design, for instance, tailored freeform surface method, discontinuous freeform surface method, continuous freeform surface method, etc [5][6][7][8]. All these methods can realize the light control of LEDs with uniform illuminance and adjustable light patterns and they have been applied in many applications.…”

Modeling on phosphor sedimentation phenomenon during curing process of high power LED packaging

“…Thus, LEDs are considered as the most potential solid-state light source for the next generation lighting and have been widely used in our daily lives [1][2][3].…”