Why Do the Lights in Your Factory Keep Flickering? It Might Be Your Power Distribution System

Why Do the Lights in Your Factory Keep Flickering? It Might Be Your Power Distribution System

Introduction

“The lights in my factory keep flickering — we‘ve changed bulbs several times and it hasn‘t helped.”

This is a common complaint from factory owners and workshop supervisors. Flickering lights are not just annoying — some equipment is sensitive to voltage fluctuations, and a single flicker can mean a production interruption or equipment failure.

Many people assume the bulbs are defective. They replace them again and again, but the problem persists.

The truth is, the issue is often not with the lights — it‘s with the power distribution system.

1️⃣ Three Common Causes of Flickering Lights

Flickering lights are essentially caused by voltage fluctuations. The following three conditions most frequently lead to lighting flicker in factories:

Cause 1: Voltage drop during startup of large equipment

• Large motors, air compressors, welding machines, cranes, and similar equipment draw 5–7 times their rated current during startup

• This causes a momentary voltage drop in the distribution system, and lights dim accordingly

• Voltage recovers when the equipment runs normally, and lights brighten again

• Typical scenario: lights flicker every time a compressor starts or a welding arc strikes

Cause 2: Insufficient power supply capacity or undersized transformer

• The transformer is operating at or near its limit — even small load fluctuations cause voltage changes

• Especially common after new equipment is added and the old transformer cannot keep up

• Typical scenario: lights are constantly dim and flicker frequently

Cause 3: Harmonic distortion

• Nonlinear loads such as VFDs, UPSs, and rectifiers generate harmonic currents

• Harmonics distort the voltage waveform, causing lights to flicker

• Typical scenario: lights flicker continuously rather than as a single dimming event — LED lights are especially sensitive

2️⃣ How to Identify Which Cause Applies?

3️⃣ How to Fix It?

If the issue is voltage drop from large equipment startup:

• Use star-delta starting or a soft starter for large motors

• In severe cases, add power factor correction or use a dedicated transformer

If the issue is insufficient capacity:

• Check if the transformer load factor exceeds 80%

• If it does, consider upgrading transformer capacity or adding an additional supply

If the issue is harmonic distortion:

• Add line reactors or active harmonic filters in front of VFDs, UPSs, and similar equipment

• In severe cases, consider supplying harmonic-generating equipment from a dedicated transformer

Conclusion

Light flickering isn‘t always a lighting problem. Identify the root cause — then fix it properly.

If you have experienced similar issues and are unsure of the cause, contact us. We can help diagnose the problem based on your equipment and recommend the right solution.

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