when functioning correctly, mains-powered fluorescent lighting has a flicker rate sufficiently high (twice the mains frequency, typically 100 hz or 120 hz) to reduce the occurrence of problems. however, a faulty fluorescent lamp can flicker at a much lower rate and trigger seizures. newer high-efficiency compact fluorescent lamps (cfl) with electronic ballast circuits operate at much higher frequencies (10–20 khz) not normally perceivable by the human eye, though defective lights can still cause problems.