Accurate Reector Design for Light Emitting Diodes

By Lee Boon Kheng, Kwong Yin Leong and Gurbir Singh

Design Guide

Abstract

The design of optical elements using the speed and

accuracy of computer-aided programs has helped in

bringing out the right product in the shortest time..

This paper will describe a method of utilizing the optical

simulation software to design a reector for LEDs with

The optical design process consists of source modeling,

correlation, optimization, tolerance and verication. Each

of the design steps are vital and interlink to each other,

hence none should be overlooked.

Reector design steps

A typical reector design involves the following steps:

1. Generate the source model (package and LED die)

2. Intensity and radiation pattern correlation between

simulated and actual measurements

3. Optimize the reector design (compound parabolic

part ASMT-MW00). The source model is generated by

taking the following steps:

1. The radiation pattern of the LED light source is

measured or obtained from the datasheet.

2. The LED radiation pattern data is fed into the ray-

tracing program (Figure 1) using the model for

multiple intensity points of radial source in the

simulation software.

3. The geometry of the LED light source is built and the

ray-tracing program is executed.

4. The radiation pattern data from the simulation result

is matched with the measured radiation pattern of the

Intensity and radiation pattern correlation (Step 2)

This correlation is done to ensure the accuracy of

the primary model (LED source). A known cylindrical

reector, of dimension shown in Figure 3b, is coupled

to the source model generated in Step 1. The simulation

result obtained is correlated to the measured data from

an actual setup shown in Figure 3a.

Figure 3a. Cylindrical reector coupled with ASMT-MW00 LED

closely matched between the actual measured and simu-

lation results. Figure 4 show the simulation layout of the

ASMT-MW00 light source coupled with the known cylin-

drical reector.

Figure 4. Simulation layout

Figure 5. Reector surface properties

Figure 5 shows the reector surface properties assigned

for the LED light source model in the ray-tracing

program. The built-in surface properties and coating

in the software has greatly increased the speed of the

when the reector surface is set to metal (mirror nish)

with specular reection. With the surface properties

and source model selected, the accuracy and speed of

producing the right design is increased.

Optimize reector design (Step 3)

Next, optimize the reector. The base surface used is a

parabolic shape of the compound parabolic concentrator

(CPC). This is a built-in surface in the simulation software,

and optimization is done by tweaking the CPC collima-

tion angle.

This has to be consider in the simulation. The critical

parameter is the surface accuracy with a tolerance of +/-

0.1 mm.

a) viewing angle is still matched

b) intensity is still within acceptable range (+/- 5%) of the

nominal intensity (i.e. 184cd)

The results also showed that dimensional variation of the

fabricated part due to manufacturing tolerances should

not be an issue.

Verication (Step 5)

The measuring equipment, Imaging Sphere was used

Conclusion

The design of reectors using software simulation must

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AV02-0633EN - September 3, 2007