We investigate the contribution of sidewall illumination in InGaN-GaN quantum-well-based light-emitting diode (LED) arrays with various cell radii. The intensity contribution from the array sidewall decreases with the increase of radius as the perimeter/area ratio is reduced. We then compare the effects of current spreading in the LED arrays of different sizes and conclude that the effect of current spreading needs to be given full consideration when the cell size in a microarray becomes larger. This letter provides a novel approach to calculate the intensity contributions of sidewall illumination and current spreading to GaN-based LED arrays.