LED illumination - timing and strobing
Because LEDs have a long but finite life span, their useful operating life can be extended by ensuring that they are only powered on when necessary, particularly as LEDs can be switched on and off with virtually no delay in reaching full intensity. As an example, if an inspection requires an exposure time of 10ms, and lighting is only required every 100ms, the lighting system only needs to be lit to coincide with the exposure, extending its usable life by approximately factor 10. This diagram shows how the life of an LED could be doubled.
This diagram shows how the life of an LED could be doubled.
It is possible to dramatically increase the LED intensity over a short duration, to coincide with the camera exposure. This is done by temporarily increasing the current flow beyond the rated continuous maximum. LEDs must be allowed time to cool between pulses, otherwise the heat generated by multiple pulses will combine and damage the diodes. The magnitude of overpowering is almost proportional to the duration between pulses. The longer the time between the pulses, the higher is the possible overdrive.
In standard set-ups, LED lighting controllers are used. They are not only beneficial when strobing or overdriving an LED system, they also provide vastly superior lighting output stability in continuous operation. As LEDs are current based devices, a small variance in input voltage will translate into a large current variation, which will then effect a large change in light output. Using current controllers, power can be adjusted directly ensuring the light intensity provides significantly better consistency and delivering more reproducible results.
