LED lights fickering

Problems with led lights flickering

When they change out all of their LED Lamps and lighting fixtures and then turn them on, they often find them flickering. There are many reasons why an LED lamp can flicker, but the most common cause is a lack of resistance in the lamp to allow the dimmer curve to work correctly.

LED lights problem

How to fix flickering or buzzing LED lights?

LED bulbs can flicker or buzz if the current (the flow of electrical charge) doesn’t remain constant. There are a number of possible causes for this:

1. Incorrect dimming set-up 

This causes flickering and buzzing, and is usually down to using the wrong dimmer switch. Your home is likely to have a ‘leading edge’ dimmer. These are designed to smoothly dim old-style bulbs in a circuit with a range typically between 200W to 1,000W.

This is a problem for LEDs that don’t need anything like that level of current in the circuit. For example, if you switch from 4 x 60W bulbs in a circuit to 4 x equivalent brightness 9W LEDs, your total wattage has gone from 240W to 36W.

‘Trailing edge’ LED dimmers (from £15) dim on a much lower wattage and will better control your lights and avoid flickering. Make sure you check the wattage rating of the trailing edge dimmer to make sure it suits the wattage of the lights in the dimmer circuit (count up the total wattage of all of the bulbs in the circuit you are dimming). Choosing a dimmer with too low or high a range will mean that you can’t smoothly dim your new LED bulbs. 

LED dimming checklist:

Buy LED bulbs that state they are dimmable.

Check whether your dimmer switch is designed for LEDs, and calculate the total wattage in the circuit to see if it’s in the right range.

Switch to a trailing edge dimmer if needed. Check the LED bulb manufacturer’s website as they may have specific recommendations.

Avoid mixing LEDs and old-style (incandescant, halogen or CFL) bulbs in the same fitting.

Ideally, use identical LED bulbs (ie the same brand /spec) in one fitting for consistency. Buying multipacks, especially of LED GU10 spotlights, is often cheaper, too.

See our top picks if you’re after new LEDs in our round-up of the best LED light bulbs.

2. A high-powered appliance in the same circuit

This is rare, but if an appliance with a heavy power draw, such as an electric fan, is on the same circuit as low-power LED bulbs, it can cause flickering. 

LED bulbs require a much lower voltage (the force needed to make electricity flow) than traditional bulbs, so they have internal drivers (transformers) to reduce the voltage to the LED bulb. Turning on the fan, in this example, can cause a momentary voltage surge in the circuit.  

The flickering you see is the drivers in the LED bulbs adjusting the voltage to suit the LED. Getting an electrician to examine your circuits will be the best way to fix such a problem.

3. Loose connections

This is one of the most common causes of flickering. If you’ve eliminated other possible causes, it’s best to get an electrician to assess if this is the problem in your home.

Dimming led lights problems

7 common LED dimming issues

Throughout the history of lighting, problems tend to emerge when new technology is introduced to the market. It’s not that LED is a bad technology that just isn’t meant to be dimmed and can only be solved through MacGyvering efforts. There were issues dimming fluorescent lamps in the early days of that technology, too.

What we’ve seen over the last few years with the challenges of properly dimming LEDs are simply growing pains and, fortunately, as an industry, we appear to be past a lot of the significant problems.

Nevertheless, a common issue with LED dimmability is sudden turn on, or turn off when you try to adjust light levels with your dimmer switch. Or you may have “dead areas” as you slide your dimmer switch. Or your LED lamps may simply flicker or flash when paired with certain dimmer switches.

Here’s how we’d describe some of those symptoms:

Drop out

This symptom occurs when you are trying to dim the lighting down and the light suddenly cuts out before you slide to the bottom of the switch.

Pop on

This is the inverse of “drop out” and occurs when you’re sliding the dimmer switch on, to increase light levels, but your LED lamps suddenly turn on at a brighter level than you would normally except.

Dead travel

This symptom is present when your lamps don’t respond to the adjustments you’re making on the dimmer switch for certain sections of the dimming scale.

Ghosting

This symptom occurs when you’ve dimmed your lamps all the way down, but they continue to glow or produce small amounts of light.

Flickering

This symptom is understood as rapid, sporadic pulsing of your lamps when paired with dimmer switches.

Strobing

Similar to flickering, strobing occurs when your lamps rhythmically flash at a less-frequent rate than a flicker.

Flashing

This is understood to be a more sporadic, infrequent symptom of bad LED dimming, occurring when the lights randomly turn on and off when paired with a dimmer control.

LEDs won’t dim? Here’s how to fix the problem

Whether your LEDs are flickering or randomly dropping out, most LED dimming problems can be avoided. Remember these four things:

Not all LED lamps are dimmable. Make sure yours are.

Not all controls work with dimmable LED lamps. Read the manufacturer’s compatibility charts.

Some LEDs are just cheap and unproven. Buy well-tested product.

Always perform a mockup.

LED lights stay on dim

It is not unusual to have leakage currents through relay coils or transistors that are supposed to be fully OFF. The driving source may leak a few milli-amps of current, not enough to turn on the relay or a series indicator lamp.

12 volt relay coils are about 400 to 1,000 ohms of DC resistance, enough to turn off a conventional lamp but not an LED.

To fix the problem add a small value resistor across the LED such that the LED voltage drops to <= 2 volts down to 1 volt. That is below the ‘ON’ threshold of most LED’s.

The leak is already there so a resistor to bypass the LED is not going to increase the leakage current. Remember there was a bulb there at one time, not impeding the flow of leakage current at all.

Measure the leak current if you can. A 1 K resistor creates a 1 volt drop across it per each mA of current flowing, so a 1 K 1/4 W resistor is a good starting point. It may have to be as low as 200 ohms if several mA of leakage current is present, but you said “dimly lit”, which implies only 1 or 2 mA of leakage current.

NOTE: ‘OFF’ is not always an ideal OFF, as this case proves. I had to use diodes often to block leakage currents from electronic modules used to control overhead lights, and sometimes used to trigger a third-party alarm. 

Often it is a transistor that is not fully OFF simply because of a cheap design. It worked at the factory with standard light bulbs, not expecting LED replacements.

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