Flickering (to us) invisible enemy

Flickering: what it is and why it matters

Artificial light is an integral part of modern life. At the same time, there is increasing scientific attention for a less visible but harmful aspect of artificial light:flickering. Flickering occurs mainly in electric light sources such as LED lamps and, even when it is not consciously perceived, can affect the human visual and neurological system.

What is flickering?

Flickering refers to rapid, periodic fluctuations in light intensity over time. These fluctuations are usually expressed in frequency (hertz, Hz) and modulation depth (the extent to which the light varies between minimum and maximum intensity). In short: the light turns on and off very frequently within a second.

Although some forms of flickering are visible (e.g., in defective lamps), much of it occurs at frequencies above the conscious perception threshold of the human eye. This is referred to as invisible flickering. Scientific research shows that invisible flickering is still processed by the visual system (Wilkins et al., 1989; IEEE, 2015).

Why does flickering occur?

Flickering is mainly caused by the way electrical current is converted into light. In many modern light sources, particularly LED lighting, an electronic driver is needed to convert alternating current (AC) to direct current (DC).

For lower quality drivers:

• the current is not fully stabilized;

• the light output follows the alternating current frequency (usually 50 or 60 Hz);

• rapid variations in light intensity occur.

This results in flickering, often at frequencies of 100–120 Hz or higher (IEEE, 2015). The higher the modulation depth, the greater the potential strain on the visual system.

Why can flickering be harmful?

The human visual system is not passive. Even when flicker is not consciously perceived, the retina and visual cortex respond to temporal changes in light (Roberts & Wilkins, 2013).

Scientific studies show that flickering can lead to increased neural activity and visual stress, as the brain must constantly compensate for the instability in light input (Wilkins et al., 2010). This effect can be amplified during prolonged exposure, such as when working or relaxing under artificial light in the evening hours.

Scientifically reported complaints

Research has linked flickering to a number of complaints, without referring to illness or permanent damage. The most consistently reported effects are:

• Headaches and migraine-like symptoms
  Several studies have demonstrated a link between light flickering and the onset or worsening of headaches, particularly in individuals who are sensitive to visual stimuli (Wilkins et al., 1989; Noseda & Burstein, 2011).

• Eye fatigue (asthenopia)
  Flickering can contribute to visual fatigue due to increased effort of the accommodative and oculomotor systems (Sheedy et al., 2003).

• Concentration problems and mental fatigue
  Studies suggest that unstable light can increase cognitive load, which can result in faster mental fatigue and reduced task performance (Veitch & McColl, 1995).

• Increased sensitivity in neurologically sensitive groups
  Individuals with migraine or photosensitivity demonstrably respond more strongly to temporal light modulation, even at frequencies above conscious perception (Wilkins et al., 2010).

It is important to note that these effects are context-dependent and vary depending on the individual, intensity, frequency, and duration of exposure.

Flickering in the evening context

Flickering can be particularly relevant in the evening hours. At this time, the visual system is in a phase in which the body is preparing for rest. Artificial light containing both blue light and flickering can therefore be perceived as particularly stressful, regardless of color or intensity (Chang et al., 2015).

Even when blue light is visually filtered (e.g., with glasses), flickering remains present if the light source itself is unstable. This explains why some people still experience symptoms under (the wrong) artificial light, despite visual protection.

Red light and flickering

Red light is often used in evening environments because it does not contain blue light and has less impact on the circadian system. However, red light sources can also flicker, depending on the electronics used.

Alina red light lamps usestable, DC-controlled drivers that maintain a constant light output. This ensures that the light intensity is continuous and free from relevant temporal fluctuations.

Alina's red light lamps are designed with a high-quality driver that stabilizes the current and thus prevents flickering within the relevant frequency range. This contributes to a calmer lighting environment in the evening, without the visual strain that can occur with unstable artificial light sources.

Conclusion

Flickering is an often underestimated aspect of artificial lighting that stems from the electrical and electronic properties of light sources. Scientific research shows that even invisible flickering can affect the visual and neurological systems, with possible complaints such as headaches, eye strain, and mental fatigue.

Reducing flickering, especially in the evening, can contribute to a calmer visual environment. In addition to color and intensity, the stability of light is therefore an important, but often overlooked, part of responsible lighting use.