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Strobe illumination

Strobing (sometimes referred to as pulsing) is the technique of activating a light only for a short period of time, and there are a number of reasons why this is done.

  • Prolonging the life of the illumination
    No matter which type of light source is used, all of them have a finite lifespan which can be dramatically extended by activating them only when required. For instance, an LED illumination might have a projected life of 10,000 to 30,000 hours in continuous mode which can be multiplied by strobing, as the light only needs to be turned on when the camera has to take an image. LEDs can be switched on and off very rapidly with little time delay or energy loss. This is of particular importance when LEDs are used in high temperature environments, because an ambient operating temperature of 40°C will reduce the meantime between failures (MTBF) by half, compared to a temperature of 25°C.

  • Increasing the intensity
    Overdriving an LED light is done by passing more current through the LED than is allowed in continuous operation. This increases the output intensity, but it can only be sustained over a short period of time, because if this were done constantly, the light would run hotter, with reduced efficiency and a reduced lifespan.

  • Freezing motion
    Multiple subsequent pulses of a light (strobing) will 'freeze' the motion of a fast moving object. This technique is often used in machine vision to capture images of objects moving past the camera at high speeds. Strobing needs to be synchronised with the objects to be inspected, so that the camera is triggered at the same moment as the pulse of light.

  • PIV (particle image velocimetry)
    PIV is a method of analysing the motion of particles in a dynamic fluid system. A strobe controller can be used to produce two pulses of light at a predetermined interval so that two consecutive images can be captured. Coupled with optical flow software, fluid movement can be analysed.

  • Biofluorescence
    In medical and other scientific research applications a strobe controller can be used in conjunction with either an ultraviolet, or an infrared light source to make biological samples fluoresce. In this type of application, the light needs to be turned on just efore an image is captured, so the high powered excitation pulse does not swamp the lower intensity emission.

This set-up requires accurate timing between the light and the camera, therefore illumination control is required to synchronise these events.

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