Is it possible to recognize a flickering LED from its technical data?


Few computer problems are more annoying than a flickering screen that appears to have no apparent cause but won't go away.

TechRepublic member Nhughes recently asked for advice

on such a problem in our

Technical Q&A


"Two of my users have reported that their screens flicker whilst they are working at their terminal," Nhughes writes. Nhughes also reports that the flickering is infrequent and the monitors sometimes flicker from the Windows desktop to a black screen. In some cases the screens even change color to a bright blue or pink. To help Nhughes and everyone else struggling with a maddening screen flicker, here are five tips to steady your screens.

Check the cables
When troubleshooting a screen flicker, I always check the cables first. Several TechRepublic members agree. Ian C B, Bruceb, Crjordan, and Aqmike all suggested checking the video and monitor power cables before doing anything else. Ian C B reminds us to confirm that the cables are...

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With fluorescent lighting gradually being displaced in favor of LED, many thought the days of dealing with flickering lights were over. Despite flickering being less present in LED than with fluorescent systems, it is certainly still a factor. What are the causes of this, and are there solutions?

Types of Flickering

There are two types of flickering with lights – visible flicker and invisible flicker. Obviously visible flicker is the one our eyes can see, which is when the light output from a given source changes rapidly. It is considered that anything below a frequency of 100Hz can be seen.

There are health concerns with visible flickering. Short-term exposure to frequencies in the 3Hz to 70Hz range are associated with epileptic seizures, with the highest possibility of occurrence being in the 15Hz to 20Hz range. With 1 in 4000 people suffering photosensitive epilepsy and many more who have not been diagnosed, this has become a public safety...

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Computer monitors have come a long way from the bulky, heavy CRTs to the sleek, modern LCDs of today. One of the most significants improvements in display technology as of late is the LED backlight, which results in a brighter, sharper picture while reducing the power consumption. Manufacturers tout the benefits of LEDs over the older CCFL (fluorescent) backlights. However, some people experience issues like unusual eye strain, pain, or headaches which seem to be caused by their new monitor. And the most likely culprit is the LED backlight flicker.

"But wait," you might say, "I thought LCD displays were supposed to be flicker-free!". Indeed, while CRT monitors redraw the whole screen many times a second (determined by their refresh rate), LCD monitors provide a constant image, simply changing the pixel colors from one to another. The speed of this process depends on the monitor's response time, which is different from refresh rate. So, the source of flicker in modern liquid...

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People keep warning about antennas like I'm gonna get killed or something. Keep in mind this is only a 75ft strip of phone/cable wire. Most people have at least 3 times that in their homes already. Just imagine how many thousands of feet the 15 story building at work has in it, yet nobody ever says "Don't go in a building, you'll get shocked or killed by lightning."

We've got 150 foot trees all over the neighborhood too yet I've never got so much as a single static shock from a door nob after walking for years on my wooden carpet covered 4 foot suspended floors. The danger from this is practically ZERO, on the other hand, I've been painfully shocked countless times by inspected and approved devices and electronic wall plugs, metal plumbing, and wall plates in multiple houses. To warn about the dangers of tiny antennas just shows complete lack of experience using such small non-powered antennas.

I've hooked a spark gap up but the charge dissipates into the air easier than...

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As many of you may have found out, not all LED lamps and/or lighting fixtures are created equal.

A common problem that we run into within our industry is when a customer wants to replace their existing incandescent lamps with new highly efficient LED lamps and/or lighting fixtures. When they change out all of their LED Lamps and/or lighting fixtures and then turn them on, they often find them flickering.

Why do they flicker?

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. This is not a new issue; it’s been around for a long time, but is becoming more “noticeable” with the major increase in LED usage.

We first saw this issue when dimmable fluorescent lamps and/or lighting fixtures became popular several years ago. The same issue occurred, because the fluorescent lamp does not have enough resistive load between the load and neutral wires (complete...

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Let’s reverse-engineer a LED, pedantic mode.

Lately, cheap electronic candles seem to be everywhere. I never paid much attention to them until recently it came to my attention that they actually use a special type of light emitting diode with integrated “candleflicker” controller. Now this is something different – who doesn’t like obscure LEDs? Half an hour later I had managed to score a bag of candleflicker-LEDs from the chinese manufacturer.

Very nice, you can not do that with real candles. But the interesting part is of course: How do they work? Considering that they literally sell for a few cents a piece, there can not be very expensive electronics involved. This raises another question: Are these cheap LEDs really worse than all the self-made microcontroller based LED-candles around the web?

The construction is relatively simple. The standard 5 mm LED package contains a small LED-Chip and a slightly larger integrated circuit. The controller...

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You may try to connect the LED to an earphone jack and stick it in your phone.
Then play music.

Don't expect too much of it.
The power you can draw is very low.

I don't have a phone with an audio jack socket so I connected an LED to the earphone socket of a radio and it worked. (By the way, if you decide to have a try, you'd better test the rig on something you don't mind frying.)

If you play a regular music file the light will flicker. You should download or create a file with such frequencies that your eyes won't be able to see the LED alternately light and dim. You may try PWM.

Rectification of the signal may help to gain some extra power but at the cost increased complexity and cumbersomeness.

I hope this may help you.

Select as Best AnswerUndo Best...

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There appears to be a bit of confusion surrounding LED and fluorescent lights. Because of this, a lot of consumers are asking the question, Why do LED lights flicker? Many of us have had occasion to be subjected to those annoying fluorescent bulbs that were tucked away under ceiling panels that would flicker whenever they were nearing the end of their life spans. Fluorescent lamps also flicker as they are turned on because it takes a few moments for the gasses to heat up sufficiently to produce light. LED lights do flicker, but not in the same way, and as a matter of fact, they flicker at such a fast rate of speed that it is usually imperceptible to the human eye.

Non-Rectified Flickering LED Lights

It is a fact that all LED lights naturally flicker at a rate of approximately 60 Hz per second. Even though that is an extremely fast rate of speed, there are some individuals who can actually detect the flickering at that rate. This is known as a half wave, also called...

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I'm no lighting expert (Russell is the man for lighting) but I think it's a safe bet that it's the transformer, and the fact that it's designed for halogen lamps.
As far as I am aware, halogen lamps have quite a long time constant (> 1s) so variation in supply will be not noticable unless it's very slow. Contrast with LEDs which have time constants in the nanoseconds and they would flicker.
So for LED driving you need a very smooth supply, which other technologies don't usually need - for instance an incandescent buld can be driven directly from an AC source at a relatively low frequency and you won't notice any flicker due to the long time constant.

I think getting a transformer specified for LEDs should solve the issue. To confirm there is variation in levels you could test the output with an oscilloscope if you have access to one. Also make sure the cables connecting the lamps are not too long and of a decent diameter (in case there is excess resistance which...

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The problem is not in the LED. The problem is the LED is misunderstood.

Almost everything associated with an LED is thermal related.

I do not know where you gathered your claims on the various devices but I doubt what you describe is the result of a single phenomena. Nor do the issues manifest in an identical fashion.

I can assure you it has nothing to do with the LED and everything to do with the LED driver and a design flaw.

If an LED device does not have a dimming feature it is still likely the LED driver will be dimming the LEDs to regulate the current.

The most likely causes would be over voltage and under voltage protection built in the driver chip or a code error when the LED is controlled by a micro-controller.

LED present a load characteristic that is much different than digital devices and other loads that require constant voltage.

Forward voltage characteristic is not just a...

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Voltage fluctuations in power systems can cause a number of harmful technical effects, resulting in disruption to production processes and substantial costs. But flicker, with its negative physiological results, can affect worker safety as well as productivity.

Humans can be sensitive to light flicker caused by voltage fluctuations. Generally speaking, flicker can significantly impair our vision and cause general discomfort and fatigue. The physiology of this phenomenon is complex (see “Tracking Human Perceptibility of Flicker” on page 30). In general terms, flicker affects our vision process and brain reaction, almost always producing discomfort and deterioration in work quality. In some situations, it can even result in workplace accidents because it affects the ergonomics of the production environment by causing operator fatigue and reduced concentration levels.

What is flicker? Basically, it's the impression of unsteadiness of visual sensation induced by a light...

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Some months ago, Lux Review opened this discussion with Dimming LED lamps: the dos and don’ts. Here we delve further into the issue and look at what it means once the decision’s taken to go ahead with a dimmable LED installation.

Here are a few things that you need to avoid:

Flicker Flashing Stuttering dimming Insufficient dimming Failed LED driver Failed dimmer

These are all inconveniences that are await you should you mismatch the electronics of the LED driver and the dimmer.

Choose the dimming method first

There are thousands of different dimmable LED light fixtures on the market, but only three major types of dimming method: mains dimming, Dali or DMX. (see box, below) So choose what kind of dimming you want before you select any LED luminaires. More lighting control manufacturers are providing lists of LED products that they have tested for compatibility with their equipment and this is a very useful service to any specifier.

Don’t buy...

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Hello everyone.

I just joined today, primarily to ask the following questions:

Here's the problem, and the symptoms. I unfortunately have a family member who has some serious emotional problems. This person, by definition, is a sociopath. He has also had drug related issues as well, and whether thats still an issue I dont know, as I dont deal with him anymore. But he's also got some friends who are simply really bad people.

So I've had problems in the past with theft, break-ins, accessing my computer without permission, etc. I am now concerned that its been accessed remotely. He does not live close to me, but he has friends who do.

I have a Dell Inspiron 1501 laptop with Win Vista. I have been noticing that every once in a while, at different times of day when I'm at home, the laptop will switch itself on without me touching it. I'll suddenly hear the characteristic two-tone noise that it makes, which is something like doot-doot, then the fan will turn...

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