Modern "electronic" fluorescent ballasts don't flicker, at least when not broken. (They use a frequency that is high enough that the phosphors' glow hasn't stop

Modern "electronic" fluorescent ballasts don't flicker, at least when not broken. (They use a frequency that is high enough that the phosphors' glow hasn't stopped before the cycle is over). The old "magnetic" ones did, but those really ought not be used anymore. They're less efficient and often flicker and hum. Bulbs at the end of their life can flicker, but those of course should be replaced.