Electrical flicker occurs when there are harmonic voltages of approximately 8-9Hz caused by the presence of harmonic currents on the electrical network. If this is applied to incandescent lamp systems this can cause a flickering effect which can be very uncomfortable for humans who may be susceptible to migraines or epilepsy. In some cases, the medical consequences can be serious.
Typical causes are electric arc furnaces, mine hoist winders and long conveyor systems, these are large loads so the effects can be spread wide on an electrical network.
Typical solutions are applied close to the source of the harmonics such as STATCOM systems, which are physically large and expensive.
Frequently those circuits which are adversely affected by the flicker are much smaller than the source of the flicker. In these cases, it may be possible to correct the voltage variation to correct the problems.