A Ray tracing calculation is performed for LED lens design which takes into account the reflection from the lead frame and side of LED. For realistic ray tracing calculation, the point tangent to the lens from the side is obtained, then, several conditions which determine the tracing function of ray are calculated. Next, the ray tracing is performed according to the plastic package and the lead frame. The ray emitted from LED chip is measured according to its direction cosines after it is refracted at lens or side. And its luminous intensity which was given at the initiating position of the ray is calculated up to the 180 degrees. Finally, the radiation pattern diagram is displayed. Examined are the effects of various geometric parameters on the radiation pattern, such as the distance between lens and lead frame and the diameter of LED package and the height between lead frame and the source of light. The simulation results are in good argeement with the test results from the viewpoint of half angle, and this suggests that the present ray tracing method may be efficiently used for LED lens design.
