The Theory of Forming the Illumination Field on the Inner Surface of an Integrating Sphere of Photometer for Luminous Flux Measurement of the LEDs

Abstract

Simplified mathematical models of the formation of the illumination field on the inner surface of the spherical photometer for three common schemes of constructive placement of the LED were proposed. The models are based on a combination of the method of successive reflections with the integration of illumination of rings around   elementary segment symmetrically illuminated by LED. Each model takes into account the main design parameters of the photometer, which affect the level of light reflectance of the inner coating, and spatial orientation of the indicatrix of LED sources. Comparative analysis of calculations of the schemes with typical parameters shows highly informative results. It is shown that the value of the reflection coefficient of more than 0,98 and the sphere diameter less than 0,6 m significantly increases impact of the volatility of these parameters on the overall error of the photometer. If the total indicatrix of LED is narrowing, the total illumination decreases when placing it on the wall of the sphere, and increases ­– when placed in the center. The results of calculations can be used to select the optimal photometer scheme for the given parameters of LED, and select the optimal parameters values of its design.