Why LEDs Flicker—and How to Stop It ?

Why LEDs Flicker—and How to Stop It ?缩略图

First, what is the reason for flickering LED lights?
In short, LED fixtures flicker when the light output fluctuates. This fluctuation occurs because dimmable light emitting diodes are designed to turn on and off at very high speeds.

Why LEDs Flicker—and How to Stop It ?插图

Second, why do LEDs flicker?
Although we can't always observe it with our eyes, all mains-powered light sources flicker - whether they are incandescent, halogen, fluorescent or LED.

The normal is an alternating current (AC) power source, supplied at 50 hertz. This means that the current that powers our lights switches back and forth 50 times per second for any light source.

The incandescent light bulbs we used to use, because of the residual heat from the bulb that kept the filament glowing between flashes, the flickering didn't seem obvious to the eye, but it was also the reason for the inefficiency of traditional light bulbs. These traditional incandescent bulbs waste about 90% of the input energy due to the amount of heat they generate!

So let's start the discussion by debunking a common misconception. Since LED light sources by their light emitting principle do not flicker, and the cause of flickering in LED lighting is caused by the power supply, it is theorized that it can be avoided altogether as long as the input power (current and voltage) is kept constant.

However the truth is that all AC power supply powered light sources will flicker, always flicker.

Third, if all lights flicker, why do some people think flickering LEDs are a problem?
LED flicker used to be a common problem. That's because - unlike incandescent, halogen and fluorescent lamps - LEDs don't last. When the LED's power is switched off, the light output stops immediately, without the afterglow effect of fluorescent lamps or the afterglow of incandescent lamps. Therefore, if connected directly to the AC mains, an LED will turn on/off 50 times per second - enough to be seen by the human eye.

This is why some people believe that LEDs flicker more than conventional sources. In the past, this used to be true. But today, thanks to advances in driver power supplies, LED stroboscopic flicker, which can have an adverse effect on the human body, can be controlled.

LED strobe is not a problem in modern LED installation projects. This is because we no longer connect LEDs directly to the mains. Instead, we use LED drivers designed for this purpose to power the LEDs.

How high-quality LED power supplies solve LED flicker problems
LED lighting requires direct current (DC) rather than AC power, so the key to eliminating LED flicker is the type of power supply you use to drive the lights.

Although the lighting industry often refers to its power supplies (aka "drivers") as simply "LED transformers," they actually do much more than just transform the voltage.An LED driver does more than just reduce (convert) the voltage. It also converts the current from alternating current to direct current. Choose a good quality LED power supply and it will also provide constant current to your LEDs. So we get no perceptible but actually flickering light.

However, low quality, simple LED drivers do not provide constant current, which is the reason why we usually recognize the saying that you can't buy cheap LED lights, and complex power supplies definitely cost slightly more. It simply converts current from AC to DC. This most basic power conversion produces an oscillating current, although it usually doubles the frequency of the input voltage, which may result in a blinking frequency of 100 times per second.

100 flashes per second is obviously much better than 50 flashes per second. But this is actually still a problem. According to a large number of experiments conducted by the LRC, when the flicker frequency of a light source is greater than 2kHz, its adverse effects on the human body through vision begin to be imperceptible, and the international standard definition of stroboscopic flicker is also defined by whether the light source affects the human body through vision or not. Further explanation is that regardless of whether the visual perception of flicker, as long as the strobe through the visual impact on the human body, it is considered to be stroboscopic in.

V. What happens to the LED when constant current = constant brightness?
Often a simple LED power supply is not enough to meet our requirements for lighting quality, then a constant current power supply is a good alternative.

These higher specification LED drivers can actually eliminate flicker by varying the voltage across the circuit to produce a constant current. The effect of AC/DC conversion is mitigated by allowing the current delivered to the LEDs to not fluctuate.

Sometimes, however, even constant-current LED drivers cannot completely eliminate flicker. Interference caused by control circuit incompatibility problems is a common cause.

Sixth, the impact of the dimming function

For most LED lighting projects and installations, the most common cause of visible flicker is the implementation of the dimming function!
Even in otherwise perfect LED lighting installations, dimming can cause problems. This is because traditional dimmers work by extending the "off" portion of each switching blink cycle to reduce the total amount of light output.
This technique is called pulse width modulation (PWM), and PWM works very efficiently - as long as the switching frequency doesn't drop to a level that the human eye can perceive.

Some manufacturers are working to solve this problem by developing LED dimmers with faster blink cycles. For example, cycles in the thousands of hertz as a goal. This would mimic the solution used in electronic ballasts that have been powering fluorescent lamps for years.

In fact, in addition to increasing the strobe frequency to the kilohertz level, the effects of stroboscopic flicker can be minimized by reducing the amplitude of the luminous flux flicker (some international stroboscopic standards such as the IEEE also correlate the amplitude and frequency of the flicker to determine whether it is stroboscopic or not). For the visible flicker generated by pulse width modulation, just do not set the LED too low, you can effectively avoid the LED flicker cycle becomes visible to the naked eye.

Seven, when the LED lamps and lanterns in the absence of dimmers flicker
The fault may be in the LED bulb, wiring or current regulation.

Sometimes the length of the wires inside the fixture may be faulty. It is good practice for all wires to be at least 6 inches in length. Loose wires connecting bulbs, fixtures, and switches can be the reason why an LED bulb suddenly starts flickering.

Poor quality LED driver assemblies cannot withstand the constant heat from other internal components. If you're a do-it-yourselfer, open up the electronics to see what's wrong and look for swollen electronics such as an inflated capacitor.

Also, away from the fixture and into the electrical panel, loose wiring in the circuit breaker is common and the cause of flickering lights.

Another factor that can cause flickering is power factor, which is the efficiency of the appliances in the circuit.

For example, connecting an incandescent bulb to the same circuit as LED lighting will cause the LED to flicker. The reason for this is that a conventional light bulb uses 100% of the required energy, most likely 60W, leaving the rest of the power for appliances such as LED lights.

Having a couple of incandescent bulbs will use up all the power very quickly and your LEDs will have nothing, which will cause them to flicker due to the lack of power.

Why LEDs Flicker—and How to Stop It ?插图2

What causes LEDs connected to dimmers to blink?

Incompatible dimmer switches connected to newer LED fixtures or bulbs can create a flicker problem, i.e., an uneven frequency of flickering (on/off at irregular intervals), indicating interference.

Often, the flickering LED problem is as simple as using a non-dimmable LED bulb on a dimmer switch. This is a simple but often overlooked problem.

The fix is as simple as replacing a non-dimmable LED with a dimmable LED bulb.

Below is an example of flickering LEDs in a living room. Note that these are non-dimmable LEDs mounted on dimmers.

Why LEDs Flicker—and How to Stop It ?插图4

Why do LEDs sometimes blink even when the lights are off?

Some LED bulbs flicker even when they are turned off. Instead of a faint afterglow for a few seconds or minutes, the dim light stays on, or there is a full blinking effect even after the switch is turned off. The most likely cause is linked to switches with fancy features.

Basically, the switch has some extra features like a dimmer, WiFi control, a night light, or even a tiny indicator light.

These smart dimmer switches will always need some backup power to make the features work.

But this is where failures can occur. The problem lies in the incorrect circuitry and wiring of the existing wall switch to the LED bulb.

Due to incorrect circuitry, the switch may not use the zero wire. the LEDs are located on the negative wire, which causes capacitive coupling, which results in residual power in the capacitor. Due to this stray capacitance and current leakage, enough voltage can build up in the circuit to cause the LED to glow or blink.

X. Summary - How to Stop LED Flickering
Over the past decade, LEDs have been heavily promoted by the lighting industry and the state as the energy efficient lighting solution of the future. However, in order to minimize the effects of LED stroboscopic flicker, we can focus on the following product information:

  1. always use an LED power supply designed for the job to drive the LED product. 2.
  2. Any LED strip driven by an AC power supply will strobe. 3.
  3. Make sure all LED products are compatible with the control circuit and power supply you are using. 4.
  4. Check for loose wiring and other faulty connections. And make sure your LED dimmer is not overloaded. 5.
  5. Consider using a constant-current LED driver. 6.
  6. When installing a dimming system, try to see if there is a minimum dimming level that you should not go below. 7.
  7. For dimming systems, consider using a zero to 10V or digital voltage dimming system.

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