Led Luminous Intensity Distribution Characteristics Of Test Methods And Systems

LED (light emitted diode) is now widely used in the field of illuminating engineering as well as information technology, and is expected to be one of the uppermost light sources in the future. Despite of the wide and rapidly growing application of LED, the reliable method for its photometric measurement is worth while to be researched.Based on the photometry, the related methods and standards of LED's photometric test are studied, a system scheme is presented for measuring the luminous intensity distribution characteristics of LED, which structure and optical characters are considered. In addition, the test condition, operation procedures, and the measurement uncertainty are discussed.For the hardware of the system, the single-chip computer of AT89C52 is adopted as the MCU (micro-controller unit), and the photoelectric transformation and signal amplification circuit are designed for the sampling channel. A high-speed 16bit A/D converter is used to ensure the precision and respondent rate, while the data communication with PC (personal computer) is realized via RS-232 serial port. Meanwhile, the PC controls the MCU to drive the step-motor to implement the whole measurement process.The system software is comprised by the MCU program and the PC program. The MCU system software includes the modules of step-motor driver, signal sampling, and data communication, all of which are controlled by the PC. The PC directs the rotation of the step-motor, by means of RS-232, to implement the photometric measurement and its calibration of the LED. Then the data processing is performed, and the measurement results are displayed on the user interface of PC, including the photometric parameters such as the maximal luminous, misalignment angle, spread angle of light beam and the spatial distribution curve for the luminous intensity of the LED.A series of experiments are carried out to evaluate the photometric measurement performance of this system. The experimental results of the typical LEDs show that the measurement meets the specification of related standard, the performance is reliable and stable, thereby the system is applicable to industry. Finally, the aspects of this study are summarized, and the possible improvements in this scheme are proposed.