Philips Electromagnetic Lamp manual Stroboscopic effect and striations, 142

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3.17 Stroboscopic effect and striations

Stroboscopic effect and striations

For this subject, see also section Lamps, 3.10.

1.A fluorescent lamp operating on an alternating current will exhibit a fluctuating light output, because the lamp extinguishes and restrikes every half cycle of the supply. So this light ripple has a fixed (mains) frequency and can cause the stroboscopic effect. It mainly depends on the used phosphors of the lamp: the use of phosphors exhibiting little or no afterglow may result in more pronounced fluctuations.

The use of inductive (Fig. 136a) and capacitive circuits together in a duo or ‘lead-lag’ combination reduces the light ripple (Fig. 136b) In an inductive circuit the lamp current will lag behind the supply voltage by approx. 60º, while in the capacitive circuit the current will be ahead of the voltage by approx. 60º.This means that the light output of a twin-lamp duo-circuit has two components mutually shifted by 120º.

The best solution for preventing the stroboscopic effect is spreading the lighting over the three phases of the supply (Fig. 136c), where the minimum light output of one lamp coincides with high light outputs of the two other lamps.

a)

b)

Fig. 136. Prevention of the stroboscopic effect by using combined inductive and capacitive circuits (‘lead-lag’ or duo-circuit) and by spreading the lighting over the three phases of the supply.

c)

1 cycle

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0	90	180	270	360

1 cycle

˚	˚	˚	˚	˚
0	90	180	270	360

1 cycle

˚	˚	˚	˚	˚
0	90	180	270	360

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