Precise optical model of multi-chip white LEDs

Wei-Ting Chien,Ivan Moreno,Ching-Cherng Sun

doi:10.1364/oe.15.007572

Abstract

A single-chip white light LED is commonly modeled by considering the phosphor coating as a homogeneous Lambertian light source. However, this approach leads to an incorrect optical simulation of phosphor-coated multi-chip LEDs due to the presence of a previously unreported spatial distribution of emission spots across the phosphor layer. We introduce "weighting" factors based on position-dependent light strength across the phosphor surface in order to improve the model accuracy. Following the modeling algorithm in the mid-field region, we have built up a precise and practical optical model by using Monte Carlo ray tracing and weighting factors. We measure the LED radiation distribution at several representative distances to test the model performance. In all cases, the accuracy is higher than 99.5% in normalized cross correlation between the simulated pattern and experimental measurement.

Highlights

An LED (Light Emitting Diode) has more advantages than a traditional light source, e.g., vivid colors, long lifetime, faster response, environmentally friendly, etc [1]
For the general case, when trying to model a single-chip white LED, the top surface of the phosphor layer is traditionally regarded as the starting Lambertian light source for Monte Carlo simulation
It can be observed that the normalized cross correlation (NCC) is always larger than 99.5%

Summary

Introduction

An LED (Light Emitting Diode) has more advantages than a traditional light source, e.g., vivid colors, long lifetime, faster response, environmentally friendly, etc [1]. Received 16 Apr 2007; revised 1 Jun 2007; accepted 2 Jun 2007; published 5 Jun 2007 June 2007 / Vol 15, No / OPTICS EXPRESS 7572 commercial phosphor-coated multi-chip LEDs, the phosphor is dispersed within an epoxy resin that surrounds a chip array. This type of LED emits a light pattern difficult to model with conventional design tools. Because each type of LED has a specific radiation pattern (due to a particular chip structure, package, and other factors), it should be precisely modeled.

Conventional model

Observing the energy distribution

Precise model and measurement

Findings

Conclusion