LED flickering or blinking: causes and solutions

Why LEDs flicker and filament lamps did not

An LED runs on low-voltage direct current. The driver converts 230 V mains into a constant current, and anything that disturbs that conversion shows up in the light at once. A filament smoothed out fluctuations through its thermal inertia; an LED responds within microseconds. Flicker is therefore rarely a fault in the LED chips themselves. It is a signal from the driver, the dimmer or the supply.

Distinguish two forms. Irregular blinking points to an interruption: a loose terminal, too little load on a dimmer or a driver tripping its protection. A steady 100 Hz shimmer, visible as moving bands on a phone camera, points to ripple in the driver. The current European ecodesign requirements for light sources limit flicker (PstLM no higher than 1.0 and SVM no higher than 0.4); good drivers stay well below those values.

Cause 1: dimmer and LED do not match

A common complaint in homes, hotels and offices. An old dimmer for incandescent or halogen lamps uses leading-edge phase control and has a minimum load of often 40 to 60 W. Replace eight 35 W halogen spots with 5 W LED spots and only 40 W remains on the dimmer: right on or below its lower limit. The result is flicker at the lowest setting, a lamp that will not switch off or one that lights up on its own.

Choose an LED dimmer with a low minimum load that handles both leading-edge and trailing-edge control, such as the LED rotary dimmer in the Liregus Modern range rated from 3 to 100 W; trailing edge is the smoothest mode for most LED drivers. The rotary dimmer in the Liregus Alfa range, rated 40 to 400 W, suits larger loads. Put only lamps of the same type on one dimmer; a mix with non-dimmable LEDs almost always flickers. Set the dimmer's minimum level just above the point where the weakest lamp burns steadily.

Cause 2: loose terminals, long cable runs and voltage dips

A loose neutral in a junction box or ceiling box is a classic cause of irregular blinking, often on several luminaires at once. LED drivers draw short, sharp current pulses; on a terminal that is slightly too loose, the voltage drops briefly with every pulse. So check all terminals in the circuit first, use ferrules on flexible conductors and re-seat spring terminals. Work with the supply isolated.

In industrial halls flicker often comes from voltage dips: a compressor, lift or welding set on the same circuit pulls the voltage down for a moment. Most drivers are specified for 230 V plus or minus 10 percent, roughly 207 to 253 V; a dip well below that lower limit makes the LED drop out. Put lighting on its own circuit, spread heavy loads across the phases and, on long runs, choose a larger conductor size to keep voltage drop below the recommended 3 percent. Outdoors, the 10 kV surge protection of VIA street luminaires on a lighting column with a 60 mm spigot protects the driver against spikes from the grid.

Cause 3: the driver itself

A driver is a power supply with electrolytic capacitors, and those dry out. A driver that has run for years at 60 or 70 degrees lets through an ever larger 100 Hz ripple: the light shimmers softly at every level, even without a dimmer. Other signs: flicker as soon as the housing is warm, or dropouts that disappear after cooling down (thermal protection). If a UFO with a plug-in sensor dims deeper in standby than the driver can handle, raise the standby level.

With 1-10 V dimming the cause is sometimes the control line. The signal is analogue; if that conductor runs parallel to the power cables, induction makes the control level wander and the luminaire flickers at its lowest setting. Use a separate, preferably screened control cable. DALI-2 is digital and far less sensitive to this: in ATRIA luminaires with a DALI driver, flicker is almost never caused by the control signal. With PWM-dimmed drivers, check the switching frequency: low frequencies produce a stroboscopic effect on rotating machinery, dangerous in a production hall.

How to test the cause in five steps

• Establish the scope: one luminaire points to the driver or its connection, the whole circuit to the dimmer, the supply or a shared terminal.
• Film the light with the slow-motion function of your phone (for example 240 frames per second). Moving bands mean 100 Hz ripple from the driver.
• Disconnect the dimmer and connect the luminaire directly. If the flicker stops, the problem lies in the dimmer or the minimum load.
• Measure the voltage at the luminaire terminals while heavy loads switch on. Dips well below 200 V explain dropouts.
• Swap the driver, or with a UFO high bay the complete luminaire, for a known good unit.

Repair or replace

Replacing a separate driver pays off in luminaires with their own driver compartment, such as the flat high bays in the ATRIA range (IP65, UGR<21) with a Meanwell driver. In compact UFO high bays the driver is usually built in; a complete 100 W UFO from the ATRIA range costs between 71 and 119 euros excluding VAT, often less than an extra hour of access platform time. In a hall with dozens of luminaires of the same age, do not replace one unit but plan the whole group: the rest usually follows soon after.

Lichtplein supplies businesses only and gives up to 5 years warranty on luminaires. If a luminaire flickers within the warranty period without a dimmer and without an external cause, send us the article number and a short video via contact. When replacing a complete installation, a lighting calculation helps you choose the right quantity and the right dimming method straight away.

Frequently asked questions