Voltage variations that lead to visually perceptible changes in lighting are called flicker (or flicker). Although often dismissed as an 'optical inconvenience', flicker is a serious Power Quality phenomenon in industrial and business environments. It indicates instability in voltage, which can lead to failure of sensitive equipment, health complaints among employees and non-compliance with grid codes.
In electrical installations where heavy, alternating loads are active - such as welding robots, shredders or heat pumps - rapid variations in mains voltage occur. When these variations reach a certain frequency and amplitude, the human eye experiences this as the restless flashing of light. For the installation manager, however, this is more than a complaint about the lighting plan; it is a concrete symptom of insufficient short-circuit power or excessive load dynamics.
In this article, you will read what exactly flicker is, how the standards (Pst and Plt) work and what steps you take to ensure operational reliability.
What is it: Rapid, repetitive variations in mains voltage leading to changes in light intensity.
Cause: Rapidly switching large loads (spot welding machines, rollers, heavy motors) or a grid that is too weak.
Risk: Staff nuisance/fatigue, control electronics failures and shortened component life.
Standardisation: laid down in EN 50160 and IEC 61000-4-15. Critical limit value is usually Pst < 1.0.
Solution: Measurement (Class A), reduce source impedance or apply dynamic compensation.
Knowledge about flicker is essential for Electrical Engineers, Maintenance Managers and Installation Managers working in:
Technically, flicker is an amplitude modulation of the 50 Hz sine wave. The voltage does not drop far once (as in a voltage dip or 'sag'), but varies continuously and rapidly around its nominal value. These variations have frequencies in the range to which the human eye and brain are sensitive (typically between 0.5 Hz and 35 Hz).
To quantify flicker objectively, we do not use the unit Volt, but a perception model defined in the standard IEC 61000-4-15. This model simulates the response of a light bulb and the human eye/brain system.
The severity of flicker is expressed in two values:
Note: A Pst value of 1.0 does not mean that the lights go out. It means that under standard conditions (reference lamp) 50% of people would find the light variation annoying.
Flicker is almost always caused by an interaction between a variable load and the impedance (resistance) of the feeding grid.
Imagine you are showering (your lighting) while someone else is quickly opening and closing the tap (the variable load). If the water pipes are narrow (high mains impedance), the jet of water will fluctuate at your place. In the electrical system, a high current demand across the mains impedance causes a voltage drop. Therefore, if this current demand varies rapidly, the voltage also varies.
Besides the obvious visual effects, there are technical symptoms you can monitor:
Ignoring high Pst values carries risks beyond irritation.
Although rare, flicker at specific frequencies (between 3 Hz and 70 Hz) can trigger epileptic seizures in susceptible individuals (photosensitive epilepsy). More often, it leads to unconscious visual stress, which reduces responsiveness and increases the risk of occupational accidents.
Electronic components, such as server or medical equipment power supplies, are designed for a stable input voltage. Continuous modulation of this voltage causes thermal stress in capacitors and coils. This results in accelerated ageing and unexpected failures ("early failures").
If your installation causes flicker that acts back on the public grid, you may be violating the grid operator's connection conditions. This can lead to fines or, in extreme cases, penalty payments to shut down the installation until the problem is resolved.
Solving flicker requires a structured approach. There is no one-size-fits-all plug you plug in.
Before investing in hardware, identify the source and severity. For this, our engineers perform a Power Quality measurement with Class A analysers. Here, we look specifically at:
Sometimes an adjustment in operations can already reduce disruption:
When operational adjustments are not enough, technical interventions are required:
Nuance: A standard capacitor bank is often too slow to compensate for fast flicker and may even exacerbate the problem due to resonance. Always opt for systems with fast response time (within milliseconds).
Replacing only the lamp: Switching to LED does not solve the cause (voltage variation) and can sometimes worsen the visual effect due to poor driver compatibility.
Relying on a standard UPS: A simple line-interactive UPS often switches to battery operation too slowly or continuously on flicker, leading to rapid battery wear. Only double conversion (online) UPS systems filter flicker effectively for the connected load, but do not solve the problem on the main busbar.
Using capacitor banks: Conventional reactive current compensation is too slow for the dynamics of welding machines or shredders.
Blame the grid operator directly: In many cases, flicker arises within one's own installation (behind the meter). Without measurement, discussion with the grid operator is hopeless.
Want to tackle the problem structurally? Follow these steps:
Deepen your knowledge of Power Quality with these topics:
Harmonics: How distortion of the sine wave stresses your installation.
Voltage dips (Sags): The difference between short dips and continuous flicker.
Power Quality Measurements: The basis for every simulation.
Selectivity analysis: ensure that only the right circuit breaker trips when a fault occurs.
Do you suffer from flashing lights, unexplained outages or are you unsure about the stability of your mains voltage? Don't keep guessing. Our engineers analyse your installation, identify the causes and offer a solution with guaranteed results.
HyTEPS
Beemdstraat 3
5653 MA Eindhoven
