The minimum rate of change of brightness at which flicker is no longer visible. The flicker frequency increases with brightness and with the amount of the visual field being stimulated. In a recent study, a still image flashed on and off for equal amounts of time was found to have a flicker frequency of 60 flashes per second at a brightness of 40 foot lamberts (fL) and 70 at 500. Television sets generally range around 100 fL in peak brightness (though some new ones claim over 700). The SMPTE recommends 16 fL for movie theater screens (though this is measured without film, which reduces the actual scene brightness by at least 50 percent). One reason for interlaced scanning is to increase television’s flashing pictures to the flicker frequency, without increasing bandwidth.