1 Introduction The light-emitting surface characteristics of the LED light-emitting tube are generally divided into a round lamp, a square lamp, a rectangular, a surface light-emitting tube, a lateral tube, a surface-mounted micro tube, and the like. The circular lamps are divided into φ2mm, φ4.4mm, φ5mm, φ8mm, φ10mm, and φ20mm according to the diameter. The shape of the light exit surface used in the LED package and the position of the LED chip from the top lens determine the LED viewing angle and light intensity distribution. Generally speaking, the larger the LED viewing angle is, the smaller the maximum luminous intensity is, but the luminous flux accumulated on the entire three-dimensional hemisphere is unchanged. The half value angle (or half power angle) of the LED is the angle between the direction in which the intensity value of the light is half the intensity value in the optical axis direction and the direction of the optical axis. The double of the half value angle is called the angle of view of the LED. The luminous intensity of the LED changes with the observation angle, and the LED luminous tube is observed from different angles, and its luminous intensity is greatly different. The magnitude of the luminous intensity is determined by the angular distribution curve of the luminous intensity of the LED light-emitting tube itself, and its distribution curve is shown in FIG. The relative optical intensity of the LED optical axis direction (ie, the ratio of the luminous intensity to the maximum luminous intensity) is 1, that is, the luminous intensity is the largest. The larger the angle from the direction of the optical axis, the smaller the relative luminous intensity. The half value angle of the LED can be estimated from Fig. 1, and the viewing angle value is. In order to meet the requirements of the large viewing angle display effect of the LED display screen, an LED light-emitting tube with a large viewing angle is generally selected. This paper analyzes the LED light-emitting tube with a rounded surface.
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The electronic industry standard SJ/T11281-2003 " LED display test method" promulgated in 2003, in which the measurement of brightness uniformity is based on the theory of colorimetry, the measurement data has nothing to do with human vision, and does not involve the observer. Factors such as spatial position and changes in viewing angle. Since the LED display screen is a large-screen display product, it can give people visual effects. Therefore, it is necessary to observe the LED display screen from different angles, and qualitatively analyze the influence of different viewing angles on the brightness uniformity of the LED display screen, so that Give a more objective evaluation of the LED display.
2, LED viewing angle