strobe lamp

The strobe lamp is a multiple flash lamp that has the ability to illuminate a moving object.

Device that uses the strobe lamp
We often find rotational motions (or other periodic motions) whose periods are very small, so that we cannot measure them by direct observation. Thus, we need to adopt other procedures.

One possibility is to illuminate the moving object with a multiple flash lamp, ie a strobe lamp. This lamp turns on and off periodically, with a frequency that can be varied. We vary the frequency of the lamp until the moving object appears to be stationary. In this way, knowing the frequency of the lamp, we can determine the frequency and period of the object under observation.

Thus, under the illumination of a strobe lamp, if we make a P mark on one of the blades of a helicopter’s propeller, we will see that this mark will appear to us to be stationary.

the strobe effect

In cases where the period of the strobe lamp is not a multiple of the period of the mark, it will not appear stopped, that is, it may show an apparent movement , with an apparent frequency lower than the real frequency, in the same direction or even in the opposite direction. to the actual motion.

Another example that we can cite is that of having observed, on the streets, that the wheels of automobiles seem to turn slowly. This is because the lamps used in public lighting, in these cases, are strobe lamps, so this effect is called strobe effect .


The strobe effect also occurs in film and television. Sometimes we have the impression that the wheels of automobiles or the blades of the propeller of a helicopter that appear on the screen rotate very slowly or even in the opposite direction to the real direction.

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