Technique employed on some cathode ray tube television sets for slowing down or speeding up the electron gun as it scans or paints each horizontal line of information. The beam is slowed down to reproduce areas of bright light and sped up on areas of low light or low brightness. he process of scan velocity modulation causes distortion in the output if dark and light colors are close together or contained within one another. Dark areas tend to become larger and light areas smaller than they should be. The technique causes phosphors in light areas of an image to be overdriven and produce too much light output (blooming) and reduce detail. can velocity modulation is sometimes listed as a valuable feature, but in fact it causes picture distortions. It is best to look for a television that does not use this technique or on which the technique can be turned off.