flickering light


i created a scene that contains an object(8 verties) and a stationary lightsource which points at the object.
The problem:
when the object moves relative to the viewpoint, the object seems to flicker. If the object moves quick toword the viewport it seems to be darker, if the object moves back from the viewport it seems to be brighter. If the object moves only “one strp” at the time it starts to flicker darker/brighter (with respect to the moving direction) for a little moment. Doublebuffering is supported by my programm, i use a Voodoo 3 graphic-card.

Has anybody an explanation for this?