Light and how to swing it

Fluctuations in brightness (flickering) as typically occurs with incandescent lamps connected to the normal mains supply (230V/50Hz). The flicker occurs 100 times per second (= 100 hertz). The light intensity variation is between 5 and 15%.

brightness fluctuations (flickering) of compact fluorescent lamps (energy-saving lamps) with electronic ballast connected to the normal power supply (230V/50Hz). The flickering is a mixture of different frequencies – some of which are very high (

20’000 Hz) – which smoothes the light waves. Depending on the model, the flickering may be stronger or weaker than shown here.
Compact fluorescent lamps with conventional magnetic ballast show much more pronounced flicker at 100 hertz

Brightness fluctuations (flickering) of fluorescent tubes (neon tubes) with magnetic ballasts. The flickering at 100 hertz is more visible (about 40%) than with incandescent lamps. Depending on the magnetic ballast the flickering can be more pronounced than shown here.

Brightness fluctuations (flickering) of fluorescent tubes (neon tubes) with electronic ballasts. Depending on the model of the electronic ballast, the flickering may be more prominent than shown here.

Brightness fluctuations (flickering) of LED lights with a high quality switching driver connected to the normal mains (230V/50Hz). The driver converts the AC current for the LED into stable, smoothed DC current. Depending on the LED lamp model, flickering can be either barely present or very noticeable – up to the maximum level shown below.

Brightness fluctuations (flickering) of LED luminaires with a low-quality switching driver. The pulsating DC current that powers the LED is not smoothed: the LEDs switch on and off 100 times per second (100 Hz).
Depending on the type of their switching driver, LED luminaires can exhibit all kinds of flickering with different amplitudes and frequencies.
If LED lights are connected to an insufficiently calibrated dimmer, even high quality LEDs can exhibit massive flicker – even at highly visible frequencies (50 hertz for example).

Most lamps show a "flickering"

Most light sources (incandescent bulbs, lamps, garlands, LED headlights or LED taillights, etc.) can be used in the car.) do not emit a regular stream of light, but flicker without us being aware of it. If one speaks of this Flicker or Flickering light, is usually called Flicker used.

Even if you don’t see the flicker directly, it can still cause discomfort, decrease performance at work as well as cause eye fatigue or trigger migraines. For some people, the flicker can even cause epileptic seizures. The degree of discomfort depends in particular on the frequency of the flicker, the amplitude of the brightness fluctuation and the intensity of the illumination. Flickering is especially annoying when reading or doing work that requires fast movements.

Very fast flickering we can not see

If a lamp is switched on and off faster and faster, at some point a perception threshold is reached where we have the feeling that the lamp remains on continuously. This phenomenon is attributed to the refresh rate of the image. This refers to a characteristic of human vision in which an afterimage of the images alternating in rapid succession remains on the retina and is superimposed by a new image. For most people, the illusion of continuous light is experienced when the light is switched on and off about 60 times per second, or in other words, when the flickering reaches a frequency of 60 hertz. But there are also people who are disturbed by the flickering of a lamp of almost 100 Hertz. In addition, studies show that our organism can feel the brightness fluctuations of a lamp up to about 200 Hertz – even if this is not visible to our eyes – and even more so if the brightness fluctuations have large amplitudes. On the other hand, flickering in the order of 1000 Hertz can also be annoying if the light source is moving quickly or if the viewer is moving.

Pets such as dogs, cats or birds are generally much more sensitive to the flickering of lighting fixtures than we humans are.

Conventional incandescent lamps and halogen lamps flicker

The electric current supplied by an ordinary power outlet in Europe (230V/50Hz) is called alternating current, because it does not flow in a single direction, but back and forth. This change occurs at high speed: 50 times per second the current changes direction – hence the 50 hertz (Hz). At the moment the current changes direction, no electricity flows – this happens twice every fiftieth of a second. Therefore, in the case of an incandescent lamp (conventional model or halogen lamp) connected directly to the wall socket, the current is interrupted 100 times per second: the flicker frequency reaches 100 hertz. At this frequency, the metallic filament of the incandescent lamp does not have time to cool down enough to stop emitting light: the light intensity decreases only in the range of 5 to 15%.

Low voltage halogen lamps (12 or 24 volts), which are powered by a transformer, usually also flicker at 100 hertz. The amplitude depends on the type of transformer, but also on the selected light intensity.

The flickering of fluorescent lighting depends on the "ballast" ballast

A fluorescent (neon) or compact fluorescent (energy-saving) lamp emits light due to a rapid sequence of electrical discharges in mercury vapor. The "flashes" produced in this way from ultraviolet light (invisible to us) excite a fluorescent powder, with which the inside of the glass body of the lamp is coated, which produces light visible to our eyes.

The strength of the flickering depends on the frequency of the discharges. Fluorescent tubes with a magnetic ballast (holder of a cheap tube) have a much more pronounced flicker at 100 Hertz than conventional incandescent lamps: the difference in intensity is in the range of 40%. On the contrary, fluorescent tubes with an electronic ballast in the base (higher price) provide a quasi flicker-free light, because the discharges take place at such a fast cadence (5’000-40’000 Hz) that the light emission through the powder remains approximately constant.

Modern fluorescent lamps are usually equipped with an electronic ballast and show relatively little flicker. In the first generation of these lamps, however, the base still contains a magnetic ballast, which can cause flickering that is perceived as unpleasant.

If fluorescent tubes flicker noticeably, the reason can also be the wear of their power supply or the tube itself.

Good LED lamps are practically flicker-free, others have significant flicker

LEDs are electronic components that react very quickly with electric current: as soon as they are no longer in contact with electricity, they no longer emit light. In addition, they operate with so-called "direct current – i.e. current that always flows in the same direction. To convert the alternating current from the wall socket into direct current, an electrical transformer is built into the base of the LED lamps (driver in English). In LED lighting for the living room, office or bedside table, this switching driver (or driver for short) is usually integrated into the lamp socket or hidden in the lamp base. The driver is there to reduce the voltage (to about 1.5 – 3.5 volts) and convert the current so that it only flows in one direction. If it is a high-quality driver, it can also smooth the current, which thus flows regularly, and the LEDs emit light that almost doesn’t flicker (or at least barely). That’s why good LED bulbs or LED lamps are practically flicker-free – and the best ones even have a completely homogeneous light emission.

For reasons related to energy efficiency* and manufacturing costs, some LED lamps also have drivers that smooth the current only unreliably or even not at all. At 100 hertz, these LED lamps flicker with a very large amplitude, or oscillate with a combination of much faster and different frequencies. In the worst case, the light is actually turned off 100 times per second (100% flicker). In the LED garlands used for decoration, this error occurs very often, some even have 100% flicker at 50 hertz: and this is not only very annoying, but even dangerous for people suffering from photosensitive epilepsy.

Flickering does not have to be indicated compulsorily on the packaging

The manufacturers of LED lamps are not (yet) obliged to declare the flicker value on the packaging. However, for some brands you can find this information on the Internet. However, it is important to know that two lamps of the same type from the same store shelf may exhibit different degrees of flicker due to the quality differences of their electronic components. It can also happen that the switching drivers are designed differently, although the lamps look exactly the same.

With LEDs, the dimmer switch can be the cause of flickering

LInstalling LEDs compatible with a light controller (dimmable) to replace incandescent or halogen spotlights connected to a dimmer switch (dimmer) can cause the lighting to exhibit severe flicker, both at 100 hertz and at much lower and highly visible frequencies (for example, 50 hertz). If the brightness is set to the maximum, the flickering is hardly visible, but it can become annoying if you turn down the illumination. It can even happen that the new lamps switch off as soon as the brightness is reduced, because they do not consume enough power compared to the former lamps all together. For the same reason, the dimmer may work correctly when a first LED bulb is combined with other halogen bulbs, or it may not work when LED bulbs are used everywhere. To protect the LEDs and ensure flicker-free visual comfort, it is generally better if the dimmer is adapted to the LEDs.

Brightness changes with pulse width modulation (PWM)

With a "PWM-Dimmer (in English Pulse Width Modulation = PWM, or in German "Pulseweitenmodulation") does not reduce the brightness of the light when you set the twilight function: it is the light pulses that become shorter and shorter in relation to the duration of the off-time.
The frequency of the pulses shown here is 100 Hertz.

Some dimmer switches (Dimmer) do not reduce the light intensity by decreasing the electric current flow, but by sending shorter and shorter light pulses to the lamps: the lower the illumination, the shorter the light pulses. Our eyes receive less light and – due to the refresh rate on the retina of the eye – we have the illusion that the environment is less bright… This type of dimmer switch is called a "pulse width modulation" dimmer called (in English Pulse Width Modulation = PWM)

But because the LEDs turn off between each light pulse, a PWM dimmer can produce a very strong flicker when the light is filtered. The frequency of the pulses, which can range from 100 Hertz to 1000 Hertz, determines the level of discomfort. The higher the frequency, the less the flickering is perceived as annoying from the start.

As the name implies, "direct current" works-Dimmer not on the pulses, but on the amount of current supplied to the lamp. Due to the low voltage at which LEDs are operated, this type of dimmer switch is more complex to manufacture. And LEDs can tend to change their light color in lower light levels.

But there are dimmers that combine the DC current and the pulse width modulation. Another option is to dispense with the dimmer and use LED lamps that provide 2 different intensity levels of illumination when you press (or hold down) the light switch several times in a row. This is a good solution to avoid flickering altogether.

many LED screens (computers, TVs, tablets) use lighting with pulses of light to control brightness. This is also the case with the LED taillights of vehicles, to change from the reverse light (weak lighting) to the brake light (strong lighting).

Disturbances in the power supply system can increase flickering

Voltage changes in the power grid can cause a "flicker effect" in lamps elicit. They can come from the movement of the lift in the building or from electrical devices with very high energy consumption that are active in the environment.

Detect and measure flickering of the lighting

To accurately measure the frequency and intensity of a lamp’s (or screen’s) flicker, a Flickermeter use. It’s as big as a cordless phone, and some models can also analyze the main characteristics of the lighting: the light spectrum, the IRC color rendering index, the color temperature (

The flickering can also be controlled with the help of a Smartphones be uncovered. Select the "Photo/Camera" mode and hold it very close to the lamp until the automatic brightness adjustment darkens the image. If the lamp has a flicker that does not exceed 200 hertz, you will see light and dark bands moving on the screen: these are the interference fringes between the brightness changes of the lamp and the images successively displayed on the smartphone screen – the image is usually "refreshed" 30 times per second (30 hertz). Very fast flickering of 1000 Hertz and more is generally not measurable.

A strong flickering can also be measured by holding the hand or a Ruler wagging back and forth very quickly in the light of the lamp (but only the lamp under test may be switched on). The flicker behaves like a disco light with strobe flash: the object in motion is divided into several images. Since our lateral field of vision is much more sensitive to flicker, the phenomenon is more noticeable when waving a hand or ruler to the side of the head.

If you own a Record player you can use your stroboscopic device for speed adjustment. The line patterns attached to the platter, when viewed with a small glow lamp at 100 hertz, show a flicker. So all you have to do is turn on the turntable under the lamp you want to test and observe whether the line pattern remains stable and motionless along the entire side length of the turntable, or whether it continues to move slowly (you can’t see it with a flicker-free lamp – or under daylight). If the turntable has no pattern, you can help yourself with a small stroboscope disc for measuring the speed, which is usually sold together with the turntable.

* If the LEDs are supplied with pulsed direct current, they consume less power than if they are supplied with stable and smoothed direct current – which allows the lamp to be classified in a better category of the energy label (for example A+ instead of A). In addition, LEDs heat up less, their light quality is more stable, and their lifetime is extended. For these reasons, some manufacturers have decided to make their LED lamps flicker in the high frequency range (>1000 Hertz), while completely avoiding the flicker at 100 Hertz, which can be perceived as annoying.

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