Illumination variation inherent in the video production process is a serious problem in video shot detection. It disturbs the precision of many shot detection algorithms. The computing cost of the current illumination invariant measures is high thus lower the speed of the algorithm. A new measure is proposed in the paper to detect shots in video. The new measure is based on the edges in the frames. The edge maps are extracted first then it is thresholded and the authors take the area of the background as the illumination invariant measure to perorm the detection of shots.The effectiveness of the measure had been validated by theoretic analysis and ex-perimental results.Compared woth the existing measures,the new measure improves the speed and reserves the precision of the detecting algorithms.