Everything You Need to Know About Light Flicker

by Penglight | Date: 10th Sep, 2023

Everything About Light Flicker

Have you ever noticed that sometimes lights seem to flicker, even though they’re meant to be steady? Light flicker is a phenomenon that can be both annoying and potentially harmful, affecting not only your peace of mind but potentially, also your health, yet many people remain unaware of its causes, effects, and possible solutions. The phenomenon isn’t limited to just our humble abodes; it’s a widespread issue spanning across homes, offices, and industrial settings. It’s high time that we shed some light on this subject.

In this comprehensive guide, we’ll delve into everything you need to know about light flicker, so you can better understand its implications and determine how to avoid or address it in your home or office.

What is Flicker

Flicker refers to the rapid and consistent fluctuation in brightness levels of a light source, which can appear as a light flashing or blinking on and off. This is typically caused by variations in the electrical current or voltage going through the light source. Flicker can be noticeable to the human eye, depending on the frequency and intensity of the fluctuations.

The flicker effect needs to be distinguished from flicker itself. The flicker effect refers to the harmful effects caused by fluctuations in the luminous flux of an electric light source, which are generated by flickering. The more severe the flickering of the electric light source, the more pronounced the harmful effects of the flicker effect. Flicker and the flicker effect are two interrelated physical quantities that characterize the fluctuation depth of the luminous flux of an electric light source and the resulting magnitude of the harmful effects (referred to as the flicker effect). In other words, flicker leads to the flicker effect.

Hazards of Light Source Flicker

Light FlickerNowadays, people not only focus on the physical performance of lighting but also attach great importance to the photobiological safety of illumination. Light source flicker stimulates the human visual system and can cause discomfort. Flickering is typically categorized into visible flicker and invisible flicker based on human perception. When the frequency is higher than 100Hz, the human eye cannot perceive the flickering phenomenon, but it can still lead to eye fatigue, headaches, and other consequences. It is widely believed that this effect exists within a frequency range of up to 500Hz.

Long-term work or life under flickering light can affect the physiological and psychological well-being of the visual system. The severity of this stimulating effect or impact is related to the intensity, frequency, duration of exposure, and long-term effects of light source flicker. This impact often occurs gradually, which is why it has not received much attention for a long time. Flickering from electric light sources and its associated effects pose serious hazards to our work and daily life. So, what are the potential hazards of flicker on the human body?

The harmful effects of light on human health are the result of long-term, chronic accumulation. Developed countries around the world have conducted extensive research on this subject for a long time. The degree of harm to the human body from light varies depending on factors such as the flicker frequency and the magnitude of light intensity changes.

What are the potential effects of LED light flicker on human eyes?

Headache and Eye Discomfort: Flickering light can cause eye strain, fatigue, and discomfort. The rapid changes in light intensity can be distracting and may lead to visual discomfort, such as headaches or eye irritation. According to the report from the National Headache Foundation in the United States: “Many migraine sufferers are highly sensitive to light, and bright, flickering light can more easily trigger migraines. Slow flickering is generally more likely to trigger migraines than fast flickering.

Visual Disturbances: Prolonged exposure to LED flicker can disrupt visual perception, making it difficult to focus or perceive objects clearly. This can affect visual acuity, depth perception, and overall visual performance.

Diminution of vision: Veitch and McColl found in 1995 that compared to high-frequency electronic ballasts, fluorescent lamp systems with 100-120Hz modulation by inductive ballasts can decrease the average visual acuity of a population. This situation often occurs during reading printed materials and text on computer screens.

Reduced Visual Task Performance: LED flicker can impair visual task performance, particularly in tasks that require fine detail perception or rapid eye movements. It may lead to decreased visual accuracy, slower reaction times, and reduced overall efficiency.

Increased Sensitivity to Light: Some individuals may be more sensitive to LED flicker than others. People with conditions like migraines or photosensitive epilepsy may experience increased sensitivity to flickering lights, which can trigger symptoms or discomfort. For instance, the rapid modulation generated by continuously flashing signal lights or car taillights can attract a driver’s prolonged attention. However, diverting one’s gaze prematurely may pose a danger to the driver, as well as to individuals and objects on the road.

Disruption of Circadian Rhythms: Certain LED lights, particularly those with a high color temperature and blue light content, can disrupt the body’s natural circadian rhythms. Exposure to flickering LED lights in the evening or at night can interfere with sleep quality and disrupt the sleep-wake cycle.

It’s important to note that the impact of LED flicker on individuals can vary depending on factors such as flicker frequency, intensity, duration of exposure, and individual sensitivity. When purchasing LED light fixtures from lighting manufacturers or factories, choose the lighting that is flicker-free.

What Causes LED Light Flicker

Traditional fluorescent lamps are directly powered by 50Hz AC electricity, resulting in a flicker frequency of 100Hz. When captured with digital cameras, this can cause the appearance of water ripples due to different sampling frequencies. On the other hand, LED lamps are powered by DC (direct current), and the light emitted by LED sources is in the form of direct current (with minor fluctuations or pulsations superimposed on the DC signal). From a physical standpoint, the flickering of LED light is indeed significantly lower compared to light sources operating on AC current.

However, since the input power supply for LED lamps is still in the form of AC, it is challenging to completely eliminate the transmission of AC ripple through LED light sources. As a result, LED lamps can also exhibit flickering to some extent.

LED light flicker can be caused by several factors, including:

  • Incompatible Dimming Systems

LED lights are often used with dimmers to adjust their brightness. However, if the LED lamp is not compatible with the dimming system or if low-quality dimmers are used, it can result in flickering issues.

  • Voltage Fluctuations

LED lights are sensitive to variations in voltage. If there are fluctuations in the electrical supply, such as rapid changes or inconsistencies in voltage levels, it can lead to flickering of the LED lights.

  • Poor Quality LED Drivers

LED drivers are responsible for regulating the electrical current supplied to the LED. If the LED driver is of low quality or not properly designed, it may not provide a stable and consistent power supply, leading to flickering.

  • Electromagnetic Interference (EMI)

External electromagnetic interference from other electrical devices or nearby power lines can interfere with the proper functioning of LED lights. EMI can disrupt the flow of electricity and cause flickering.

  • Thermal Issues

Overheating of LED components can also contribute to flickering. When LED lights are not adequately cooled or when there is poor heat dissipation, it can lead to fluctuations in the light output and result in flickering.

  • Aging or Defective Components

As LED lights age, their internal components can degrade or malfunction, leading to flickering. This can include issues with the LED chips, driver circuitry, or other electronic components. Also, a loose connection either in the wiring, power source or the bulb itself can cause intermittent flickering.

To address LED light flicker, it is important to choose high-quality LED products from reputable manufacturers, so you can eliminate the flicker issue from the root. Penglight is a professional LED light sourcing agent in China. We can help you source qualified suppliers and evaluate the production.

Testing Methods for LED Flicker

To check and determine whether an LED light source or luminaire has flicker, a simple method is to use the camera function of a mobile phone and observe the LED light source up close. If you see obvious black bars scrolling or noticeable variations in brightness on the screen, it can be concluded that there is flicker. However, you can also try the following methods.

  • Visual Observation Method

This is a subjective method where the LED light source is observed directly by the human eye. Any visible flickering effects can be detected and evaluated. This method is useful for identifying obvious flickering issues but may not be sensitive enough for detecting lower-frequency flicker. Note: If the flicker can be overserved by our eyes, it means that the light fixture is defective and has severe issues.

  • Photometric Measurement Method

This method involves using a photometer or illuminance meter to measure the light intensity variations of the LED source. By recording the fluctuations in illuminance, the level of LED flicker can be assessed. This method provides quantitative data but requires specialized testing equipment.

  • High-Speed Camera Method

High-speed cameras are used to record the variations in light intensity of the LED source. By analyzing the captured video footage, the presence of flickering can be determined, and the frequency and amplitude of the flicker can be quantitatively evaluated.

  • Spectral Analysis Method

This method utilizes a spectrometer to analyze the spectral characteristics of the LED source. By detecting the frequency components in the spectrum, the presence of LED flicker can be determined. This method provides information about the frequency and amplitude of the flicker but requires specialized testing equipment and analysis techniques.

What kind of flicker depth is considered acceptable?

The demand for flicker-free lighting requires targeted development based on market needs. Currently, there are clear technical requirements in the US regulations, but most markets do not have unified standards that strictly enforce flicker depth for light sources. Some customers currently require a flicker depth of less than 8%, while others require less than 5%. There are even cases where customers demand flicker depths of less than 1%.

In many lighting applications, such as residential, commercial, or office environments, it is desirable to have minimal or imperceptible flicker. Standards and guidelines set by organizations like the Illuminating Engineering Society (IES) provide recommended limits for flicker depth, typically expressed as a percentage or in terms of flicker index values.

For example, in some standards, a flicker depth of less than 10% is considered acceptable for general lighting applications. However, for sensitive environments like healthcare facilities or areas where high-speed camera recording is involved, even lower flicker depths may be required.

It’s important to note that individual sensitivity to flicker can vary, and some people may be more sensitive to flicker than others. Additionally, certain activities or tasks, such as slow-motion video recording or critical visual tasks, may demand stricter requirements for flicker depth.


Currently, the potential hazards of LED light flicker are gradually gaining attention, and with the new technology, flicker-free lighting is not impossible. According to the latest national standards, the definition and evaluation methods of flicker, such as fluctuation depth and flicker index, can be used to assess the flicker of a lighting fixture through experiments. The methods to address flicker are still under research, but certain LED power supplies are already capable of eliminating flicker.

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