critical flicker frequency

n. The rate of flicker or variation in a visual stimulus at which the flicker disappears from perception and the stimulus is seen as constant. The rate varies among individuals and with characteristics such as brightness and size but is usually around 30 cycles per second. In the United States, television images are shown at a flicker rate of 30 per second, but each image is shown twice to increase the functional flicker rate to 60, which is well above the threshold.