Flash control
The performance of LEDs and LED lighting is often limited by the self-heating of the components. One way to increase performance is to use flash controllers or flash control units.
Since camera systems, with the exception of line scan cameras and high-speed cameras, usually only record short images at a certain frame rate, it can be advantageous to synchronize the lighting with the image recording and switch it off in the dead time between the image recordings.
In addition, it is usually possible to supply LED lighting with a disproportionately higher current for short flash durations than in continuous operation. The most sensitive part of an LED is the so-called “active zone”, in which the electric current is converted into light. With very short pulses, the active zone does not have time to heat up accordingly. For this reason, twice the current of the continuous current is often permissible in the microsecond range, even with very high-quality LEDs.
As far as the shortness of the light pulses is concerned, there is almost no restriction for the LEDs themselves. However, high-frequency effects and the required precision of the current control ensure that flash controllers can usually deliver a minimum pulse duration of 1µs. The maximum length of the pulses usually depends on the power supply of the controller and/or the internal memory capabilities of the controller. The required lightning current, the required voltage and the dissipation of the controller’s power loss also play a role.
Flash controllers usually either have fixed operating values for current, voltage and flash duration or can be configured via digital communication protocols or web interfaces. The pulses themselves are then triggered during operation either by the camera or a PLC via an analog signal or by computer-controlled digital signals.
Flash controllers for small to medium outputs can be integrated in the lighting itself or in the supply line. High-performance controllers usually consist of modules of different designs, which are often housed in the control cabinet.
See also LED driver.
