Fluorescent lamps are provided with 50Hz ac current supply. When operating under the frequencies the lamp becomes zero (crosses zero wave) double the supply frequency, i.e, 100 times for 50Hz frequency per second. Due to the persistence of vision our eyes do not notice them. However if the light falls on the moving parts due to illusion, they may appear to be either running slow, or in reverse direction or even may appear stationary. This effect is called "Stroboscopic effect".
If the industry is supplied with three phase supply, adjacent lamps should be fed with different phase so that the zero instants of the two lamps will not be same.
If single phase supply is only available, then connection of two adjacent lamps are made such that the two lamps are connected in parallel with the supply and in one lamp connection a capacitor or condenser is kept in series with the choke. This makes a phase shift thereby eliminating stroboscopic effect