LED directivity measurement in situ

The paper presents the technique of LED directivity measurement in situ. A LED far-field pattern (FFP) can be measured quickly without dismantling the LEDs from the tile. The positioning device has been replaced by lighting a single LED in a tile, so the desired inspection angle has been obtained. Irradiance data then has been corrected for distance and sensor directivity. The resulting data set has been fitted with the approximation function. The obtained approximation is the representative of the average LED FFP. Brief analysis of an approximation function has been carried out. Four simple functions have been considered as candidates for such approximation. The L2-norm of the error between the original and fitted function was considered as an approximation quality criterion. Gaussian approximation has the best performance. For in situ technique performance evaluation, several sample tiles have been measured and the obtained outcome has been compared against goniometry results. The L2-norm of the LED FFP intensity error and viewing angle error are presented.