Sprite halos are brief, diffuse flashes, which occur at the top of a sprite and precede the development of streamer structures at lower altitudes. We have investigated the characteristics of sprite halos in detail using coincident photometric and imaging data obtained during the Sprites'96 and '99 campaign in Colorado and Wyoming, USA. It is found that the average altitude of the centroid of the halo emission and the mean horizontal diameter of the halo events are ~80 and ~86 km, respectively, while the average speed of the descending motion of the sprite halos was ~4.3 ¿ 107 m/s. It was also found that the peak current intensity of the causative CG decreases with time delay from the onset of the sferics.