Power-line flicker

Under Flicker is understood according to the International Dictionary of Technical Electric the subjective impression of instability of visual perception caused by a light stimulus whose luminance or spectral distribution fluctuates with time. Flicker is thus the subjective impression of luminance changes, what you colloquially referred to as flicker or flicker of light.

But not every change in luminance (brightness variation ) is perceived as a flicker. Bemerkbarkeitsschwelle for the luminance changes is a frequency dependent variable, which indicates from which relative luminance change at a given frequency, this is perceived. The Bemerkbarkeitsschwelle was determined empirically in the 1970s on the basis of people try.

Emergence of Flicker

The operating voltage public electricity supply network is subject to fluctuations. These temporal variations may flicker may produce. The cause of this is caused at the last small internal impedance of the network by the load current of a device or device voltage drop. This supply voltage fluctuations may therefore lead to changes in light output incandescent lamps. For bulbs with electronic ballast as compact fluorescent lamps or LED lamps to the power supply voltage fluctuation usually does not affect the luminous flux changes because the electronic ballast to compensate for the variation.

Measurement of Flicker

For the reproducible measurement of flicker is a measurement circuit as shown in the illustration, it is necessary to reflect the average network impedance. Basically require flicker according to norm a network of known, low and constant over time, and without source impedance variations of the open circuit voltage.

The requirements for the Flickermessgeräte are specified in DIN EN 61000-4-15. The flicker meter is divided into five functional blocks. Block 1 is a voltage control loop. In blocks 2-4, the 230 V/60 W bulb ( reference lamp ) and the human visual system ( eye-brain model) are simulated. Block 5 is a statistics block for determining the flicker severity Pst after the procedure.

The instantaneous value of the measured flicker is specified in " Wahrnehmbarkeitseinheiten " P ( perceptibility unit). By weighted averaging over different time periods, one obtains the really important values ​​Pst (short term ) and Plt (long term).

For Pst and Plt 61000-3-11 limits in EN 61000-3-3 and DIN EN defined:

• Pst of the ATU must not exceed the value of 1.0.
• Plt of the EUT shall not exceed the value of 0.65.
• Pst source, may not exceed the value of 0.4.