A Far Field Measurement System Design for Light Emitting Devices

Abstract

The key point of the proposed LED (light emitting device) optical field measurement system is to place the packaged or unpackaged LED on a stepping motor without any translation parts. Thus the mechanical aging effect and the maintenance problems of the traditional rotary part are avoided. Besides, the measurement sensors are fixed along a quarter arc of a circle with the LED at the center, so they can take both spectrum and energy output measurements along various aspect angles. The system has thirteen photo detector modules forming a 90° arch with a diameter of 63.2cm. Each module comprises eight photo-detectors, and each detector covers 0.9°. A stepping motor, placed at the center of the circle, rotates a LED under test through 360°with a step size of 1.8°. A powerful micro-controller (C8051-F020) is employed to control the 3-dimensional far field measurement flow for the data acquisition that bridges the photo-detector array modules and a personal computer. The communication between the personal computer and the data acquisition sub-system is through a RS232 interface. A fast, reliable, user-friendly measurement system has been achieved.