Flickering, an invisible enemy (to us)

Flickering: what it is and why it matters

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

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 (for example, in defective lamps), much of it occurs at frequencies above the threshold of conscious perception 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 primarily caused by the way electrical current is converted into light. Many modern light sources, especially LED lighting, require an electronic driver to convert alternating current (AC) into direct current (DC).

With lower-quality drivers:

• the current is not fully stabilised;

• 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 greater the modulation depth, the greater the potential strain on the visual system.

Why can flickering be taxing?

The human visual system is not passive. Even when flickering 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 because the brain must constantly compensate for instability in the light input (Wilkins et al., 2010). This effect may be intensified by prolonged exposure, such as when working or relaxing under artificial light in the evening.

Scientifically reported symptoms

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

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

• Eye strain (asthenopia)
  Flickering can contribute to visual fatigue by increasing the demands on the accommodative and oculomotor systems (Sheedy et al., 2003).

• Difficulty concentrating and mental fatigue
  Studies suggest that unstable light can increase cognitive load, potentially resulting in faster mental fatigue and reduced task performance (Veitch & McColl, 1995).

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

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

Flickering in the evening

In the evening, flickering may be particularly relevant. The visual system is then in a phase in which the body is preparing for rest. Artificial light containing both blue light and flickering may therefore be experienced as additionally taxing, regardless of colour or intensity (Chang et al., 2015).

Even when blue light is visually filtered (for example, with glasses), flickering remains 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 contains no blue light and has less influence on the circadian system. However, red-light sources can also flicker, depending on the electronics used.

The Alina red light lamps use stable, direct-current-controlled drivers that keep the light output constant. As a result, the light intensity is continuous and free from relevant temporal fluctuations.

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

Conclusion

Flickering is an often-overlooked aspect of artificial light caused by the electrical and electronic properties of light sources. Scientific research shows that even invisible flickering can affect the visual and neurological systems, with possible symptoms such as headaches, eye strain and mental fatigue.

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