How to Convert Hertz in Seconds

Flicker (flicker or flicker)
of lightbulbs and lamps

Brightness fluctuations (flickering) as it typically occurs with incandescent lamps that are connected to the normal power supply (230V / 50Hz). The flickering occurs 100 times per second (= 100 Hertz). The light intensity fluctuation is between 5 and 15%.

Flicker in brightness of compact fluorescent lamps (energy saving lamps) with electronic ballast that are connected to the normal power supply (230V / 50Hz). The flicker is a mixture of different frequencies - some of which are very high (~ 20,000 Hz) - which smooths the light waves. Depending on the model, the flicker can be stronger or weaker than shown here.
Compact fluorescent lamps with conventional magnetic ballast show a much more pronounced flicker at 100 Hertz

Fluctuations in brightness (flicker) of fluorescent tubes (neon tubes) with magnetic ballast. The flicker at 100 Hertz is more clearly visible (around 40%) than with incandescent lamps. Depending on the magnetic ballast, the flicker can be more pronounced than shown here.

Fluctuations in brightness (flicker) of fluorescent tubes (neon tubes) with electronic ballast. Depending on the model of the electronic ballast, the flicker can be more pronounced than shown here.

Brightness fluctuations (flickering) of LED lights with a high quality switching driver connected to the normal power supply (230V / 50Hz). The driver converts the alternating current for the LED into stable, smoothed direct current. Depending on the LED lamp model, the flickering can either hardly be present or it can occur very clearly - up to the maximum level shown below.

Brightness fluctuations (flicker) of LED lights with a poor quality switch driver. The pulsating direct current that supplies 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 lights can have all kinds of flicker with different amplitudes and frequencies.
If LED lights are connected to an inadequately calibrated dimmer, high-quality LEDs can also have a massive flicker - even at a clearly visible frequency (50 Hertz, for example).

Most lamps show a "flicker"

Most illuminants (light bulbs, lamps, garlands, LED headlights or LED taillights etc.) do not emit a regular luminous flux, but flicker without our being aware of this. One speaks of this flicker or Flicker of light, is usually the English name Flicker used.

Even if the flicker is not seen directly, it can still cause discomfort, reduce performance at work, cause eye fatigue or trigger migraines. In some people, the flicker can even cause epilepsy. How strongly this discomfort is felt depends in particular on the frequency of the flicker, on the amplitude of the fluctuation in brightness and the intensity of the lighting. Flicker is particularly annoying when reading and when working that requires fast movements.

We cannot see very fast flickering

If a lamp is switched on and off faster and faster, a perception threshold is reached at some point where we have the feeling that the lamp remains switched on continuously. This phenomenon is attributed to the refresh rate. This refers to a property of human vision in which an afterimage is retained on the retina of the images that alternate in rapid succession and is overlaid by a new image. Most people experience the illusion of continuous light when the light is switched on and off about 60 times per second, or to put it another way: 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. Studies also show that our organism can feel the brightness fluctuations of a lamp up to around 200 Hertz - even if this is not visible to our eyes - and even more so when the brightness fluctuations have large amplitudes. On the other hand, flicker in the order of magnitude of 1000 Hertz can also have a disruptive effect 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 flicker from lighting fixtures than we humans are.

Conventional incandescent lamps and halogen lamps flicker

The electrical current that a normal socket in Europe supplies (230V / 50Hz) is called alternating current, because it does not flow in a single direction, but back and forth. This change takes place at high speed: the current changes direction 50 times per second - hence the 50 Hertz (Hz). The moment the current changes direction, no electricity flows - it happens twice every fiftieth of a second. This is why the current is interrupted 100 times per second with an incandescent lamp (conventional model or halogen lamp) that is connected directly to the socket: the flicker frequency reaches 100 Hertz. At this frequency, the metallic filament of the incandescent lamp does not have time to cool down enough that it no longer emits light: the light intensity only drops in the order of magnitude between 5 and 15%.

Low-voltage halogen lamps (12 or 24 volts), which are supplied with electricity via a transformer, usually also have a flicker at 100 Hertz. The amplitude depends on the type of transformer, but also on the selected light intensity.

The flicker of lighting with fluorescent lamps depends on the "ballast"

A fluorescent tube (neon tube) or a compact fluorescent lamp (energy-saving lamp) emits light due to a rapid series of electrical discharges in mercury vapor. The "flashes" of ultraviolet light (not visible to us) generated in this way excite a fluorescent powder that is coated on the inside of the glass body of the lamp, which produces light that is visible to our eyes.

The strength of the flicker 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 rate (5,000-40,000 Hz) that the light emission through the powder in remains roughly 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 trigger a flicker that is perceived as unpleasant.

If fluorescent tubes flicker clearly noticeable, the reason for this can also lie in the wear and tear of their power supply or the tube itself.

Good LED lamps are practically flicker-free, while others have a distinct flicker

LEDs are electronic components that react very quickly to electrical current: as soon as they are no longer in contact with electricity, they no longer emit light. They also work with so-called "direct current" - that is, current that always flows in the same direction. In order to convert the alternating current from the socket into direct current, an electrical transformer is built into the base of the LED lamps (driver in English). In the case of LED lighting for the living room, the office or the bedside table, this switch driver (or driver for short) is usually integrated in the lamp socket or hidden in the lamp base. The driver is there to reduce the voltage (to around 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 hardly (or at least hardly) flickers. This is why good LED light bulbs or LED lamps are practically flicker-free - and the best even have a completely homogeneous light emission.

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

Flicker does not have to be shown on the packaging

The manufacturers of LED lamps are not (yet) obliged to declare the flicker value on the packaging. For some brands, however, this information can be found on the Internet. However, you have to know that two lamps of the same type from the same store shelf can have different levels of flicker due to the differences in the quality of their electronic components. It can also happen that the switch drivers are designed differently, although the lamps look exactly the same.

In the case of LEDs, the twilight switch (dimmer) can be the cause of the flicker

If you install LEDs that are compatible with a light controller (dimmable) to replace incandescent lamps or halogen spots that are connected to a twilight switch (dimmer), the lighting can have a strong flicker, at 100 Hertz as well as at much lower and easily visible frequencies (for example 50 Hertz). If the brightness is set to the maximum, the flickering is barely noticeable, but it can become annoying if the lighting is turned down. It can even happen that the new lamps switch themselves off as soon as the brightness is reduced, since they themselves no longer consume enough electricity compared to the previous lamps. For the same reason, the dimmer can work correctly if you combine a first LED incandescent lamp with additional halogen lamps, or it can not work if LED incandescent lamps are used everywhere. In order 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, Pulse Width Modulation)

With a "PWM" dimmer (in English Pulse Width Modulation = PWM, or in German "Pulse Width Modulation"), the brightness of the light does not decrease when the twilight function is set: it is the light pulses that are always in relation to the duration of the switch-off time get shorter.
The pulse frequency shown here is 100 Hertz.

Some twilight switches (dimmer) do not reduce the light intensity by reducing the flow of electrical current, but by sending ever shorter light pulses to the lamps: the lower the lighting, 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 surroundings are less bright ... This type of twilight switch is called a dimmer with "pulse width modulation" (in English Pulse Width Modulation = PWM)

Since the LEDs switch off between each light pulse, a PWM dimmer can generate a very strong flicker when the light is filtered. The point at which discomfort occurs depends on the frequency of the impulses, which can range from 100 Hertz to 1000 Hertz. The higher the frequency, the less the flicker is perceived as annoying from the start.

As the name suggests, "direct current" dimmers do not act on the pulses, but on the amount of current that is fed to the lamp. Because of the low voltage with which LEDs are operated, this type of twilight switch is more complex to manufacture. And LEDs can tend to change their light color when the light is weaker.

But there are dimmers that combine direct current and pulse width modulation. Another possibility is to do without the dimmer and to use LED lamps, which offer 2 different intensity lighting levels if you press the light switch several times in a row (or keep it pressed). This is a good solution to avoid flicker altogether.

Many LED screens (computers, televisions, tablets) use lighting with light pulses to regulate the brightness. This is also the case with the LED taillights of vehicles in order to switch from the reversing light (weak lighting) to the brake light (strong lighting).


Disturbances in the power grid can increase the flicker

Changes in voltage in the power grid can cause a "flicker effect" in lamps. They can result from the movement of the lift in the building or from electrical devices with very high energy consumption that are active in the vicinity.


Determine and measure flicker in the lighting

To accurately measure the frequency and intensity of flicker on a lamp (or screen), one can use a Flicker meter use. It is as big as a cordless telephone, and some models can also analyze the main characteristics of the lighting: the light spectrum, the IRC color rendering index, the color temperature (~ CHF 1000.-).

The flicker can also be done with the help of a Smartphones to be revealed. You 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 can see light and dark bands moving on the screen: these are the interference fringes between the brightness changes of the lamp and the images displayed successively on the smartphone screen - the image is in the Usually "refreshed" 30 times per second (30 Hertz). Very fast flickering of 1000 Hertz and more is generally not measurable.

A strong flicker can also be measured by holding the hand or a ruler waves back and forth very quickly in the light of the lamp (but only the lamp to be tested may be switched on). The flicker behaves like a disco light with a strobe flash: the moving object is divided into several images. Since our lateral field of vision reacts much more sensitively to flicker, the phenomenon is more noticeable if you wave your hand or the ruler to the side of your head.

Do you own oneRecord player you can use your stroboscopic device to adjust the speed. The line patterns attached to the turntable show a flicker when viewed with a small glow lamp at 100 Hertz. You only have to switch on the turntable under the lamp to be tested and observe whether the line pattern remains stable and immobile along the entire length of the side of the turntable or whether it continues to move slowly (with a flicker-free lamp - or under daylight - you cannot see it ). If the turntable has no pattern, you can use a small stroboscopic disc to measure 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 fed with stable and smooth direct current - which allows the lamp to be classified in a better category on the energy label (for example A + instead of A). In addition, the LEDs heat up less, their light quality is more stable and their service life is extended. For these reasons, some manufacturers have decided to let their LED lamps flicker in the high-frequency range (> 1000 Hertz), completely avoiding the patch at 100 Hertz, which can be perceived as annoying.

LED lamps, Federal Office of Public Health (BAG)

Dimming of LEDs - Know how, EnergieSchweiz