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FAQ
 
FAQ Topic: 
Strobing
Problem: 
What is the advantage of strobing LEDs?
Solution: 

In machine vision, strobing is defined as flashing a light, typically coordinated with camera exposure. The timing, frequency, and duration of the strobe flash is determined by either the internal light strobe controller, or externally by a trigger event generated by a camera or part-in-place / proximity signal. LEDs lend themselves well for this activity as they are solid-state devices, rather than thermionic sources, and thus have little ramp up and down latency, and depending on duty cycle, generate little or no heat.

Strobing is most often used to freeze motion in situations where continuous inspection is not necessary, typically singulated or indexed objects on a conveyor line, an approach limited primarily by the speed of the object. The inverse relationship between object speed and camera exposure time means that light intensity, during the camera exposure period, must increase proportionally for faster moving objects, or the vision system will not have adequate illumination and contrast levels to perform the inspection.

One solution is to overdrive the LED light – in other words, push extra current through the LEDs during this shortened exposure period to boost the intensity recorded by the camera. Hence, turbo-charging LEDs, or generating more light over a shorter period of time, may be advantageous.

Strobing also extends the real-time life of an LED light. For example, a red or IR LED light operated at a 10% duty cycle (as defined by time on / total time x 100%) will have a life of 10 x 100,000 hr. or 1,000,000 hours real-time. Because of the short on-time, little or no heat is generated, further lengthening the life of the light.

Finally, overdriving strobe lights effectively overwhelms ambient light contribution, and the short exposure times may also assist in creating sharper edges, particularly if a monochrome LED light is used.