G4 LED Bulb Flickering After Installation – What's Wrong?

Replacing old halogen bulbs with LED versions is an effective way to reduce electricity consumption and eliminate excessive heat from your fittings. However, many people encounter a frustrating phenomenon after installation: the new G4 LED bulb starts flickering or pulsing immediately after switching on. Although the bulb fits the socket mechanically, the light doesn't burn steadily.

The flickering light is usually not caused by a faulty bulb. The problem lies with the system's old power supply and the electrical differences between different lighting technologies. Identifying the cause helps you fix the situation quickly without unnecessary bulb purchases.

Short Answer: Flickering Is Usually Caused by the Wrong Power Supply

Flickering of G4 LED bulbs is most commonly caused by the fixture's old electronic halogen power supply. Halogen bulbs require considerable power to function. Therefore, old 12-volt power supplies are designed to start only when a certain minimum load is met.

A typical electronic halogen power supply requires a minimum power of 10–20 watts (the power supply casing often states, for example, 10–60W or 20–105VA). When you connect energy-efficient G4 LED bulbs, which consume only 1–2 watts each, the total load is too low. The power supply doesn't recognise such a small current draw, causing its internal protection system to start and stop in a continuous cycle. This appears to the eye as rapid flickering.

Another essential factor is the type of current supplied. Halogen power supplies feed alternating current (AC) into the system, whereas sensitive LED technology requires steady direct current (DC). The frequency of alternating current causes rapid pulsing in the LED bulb, which can strain the eyes and cause headaches.

Power Supply and G4 LED Bulb Compatibility

To achieve steady lighting in a 12-volt low-voltage system, the power supply and bulb must be chosen correctly. Halogen bulbs are based on a heating filament, so they tolerate voltage fluctuations without visible interference. LED bulbs react immediately to changes in the power supply.

When you replace the system with an LED power supply that feeds direct current (12V DC), the current supply stabilises. This eliminates flickering and makes the light pleasant. At the same time, a DC power supply protects the LED bulb's electronics from voltage spikes and ensures a long service life.

Modern LED lamps and bulbs operate without minimum load requirements when paired with a DC power supply. With the right power supply, lights turn on immediately without delay or humming.

How to Diagnose Flickering Step by Step

The cause of flickering can often be identified with a few basic checks. Troubleshooting involves examining mechanical contacts, the system's minimum load and any dimmer limitations.

1. Check the G4 Socket's Mechanical Contact
G4 bulb pins are thin, and the fixture socket can loosen or oxidise over time due to heat. Poor contact causes minor sparking, which appears as light flickering. Press the bulb firmly into place and ensure a secure fit. If the light burns steadily when you gently press the bulb, the issue is a contact fault.

2. Perform a Load Test with a Halogen Bulb
If the fixture has multiple bulbs, leave one old halogen bulb in place and replace the others with LED bulbs. The halogen raises the power consumption above the power supply's minimum threshold. If the LED bulbs stop flickering, the cause is the power supply's excessively high minimum load requirement.

3. Verify Dimmer Compatibility
If the fixture is connected to a wall dimmer, the flickering may be caused by an old phase-control dimmer that doesn't work with low LED loads. Not all G4 LED bulbs are dimmable either. Check the bulb and dimmer specifications.

When Flickering Requires an Electrician's Inspection

Some repairs are easy to do yourself, whilst others require a professional. It's important to distinguish between portable fittings and fixed electrical installations.

You can safely replace bulbs and power supplies yourself in table and floor lamps that connect via a plug. Kitchen backsplash lights, fixed bathroom fittings and power supplies installed inside ceilings are part of the fixed 230-volt electrical network.

According to electrical safety legislation, replacing a fixed mains-voltage power supply is licensed electrical work that may only be carried out by a qualified electrician. Professional installation ensures correct sizing, fire safety and maintains your property's insurance coverage.

When a G4 fixture's power supply is corrected with a suitable DC power supply and quality bulbs, the lighting becomes completely flicker-free, energy consumption drops and the bulbs last a long time.