# LED pulsing and strobing

LEDs can be easily driven in a pulsed (on/off) regime and can be switched on and off in sequence, turning them on only when necessary. Usage of LEDs in pulsed mode has many advantages including the extension of their lifespan. If the LED driving current (or voltage) is set to the nominal value declared by the LED manufacturer for continuous mode, we talk about pulsed mode: the LED is simply switched on and off.

LEDs can also be driven at higher intensities (i.e. overdriven) than the nominal values, thus producing more light but only for a limited amount of time: in this case we say that the LED is operated in strobed mode.

Strobing is needed whenever the application requires an increased amount of light to freeze the motion of fast moving objects, in order to eliminate the influence of ambient light, to preserve the LED lifetime and to synchronize the ON time of your light (ton) with the camera and item to be inspected.

Duty cycles parameters.
Triggering and strobing.

To properly strobe an LED light, a few parameters must be considered:

• Max pulse width or ON time (ton max): the maximum amount of time for which the LED light can be switched on at the maximum forward current.
• Duty cycle D is defined as (usually expressed in %):
D = t_(on) / (t_(on) + t_(off))

Where toff is the amount of time for which the LED light is off and T = ton+toff is the cycle period. The duty cycle gives the fraction in % of the cycle time during which the LEDs can be switched on. The period T can be also given as the cycle frequency f = 1/T, expressed in Hertz (Hz).

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