Strobe lights can cause seizures, but only for a specific subset of the population and under particular conditions. Flashing or flickering lights, including those from strobes, video games, or natural sources, can act as a powerful visual trigger for an epileptic seizure. Understanding this reaction requires recognizing who is susceptible and the precise characteristics of the light patterns that pose a risk.
Photosensitivity and Seizures
The connection between flashing lights and seizures is defined by Photosensitive Epilepsy (PSE), which affects a small fraction of the general population. This is a form of reflex epilepsy where seizures are reliably triggered by visual stimuli that form repetitive patterns. While approximately one in 100 people has epilepsy, only about 3% of those individuals are photosensitive.
The overall frequency of PSE is estimated to be around one in 4,000 people. PSE is more commonly diagnosed in children and adolescents, especially those with certain types of generalized epilepsy. Feeling disoriented or uncomfortable when exposed to intense flashing lights does not indicate a person has photosensitive epilepsy.
How Flashing Lights Affect the Brain
The underlying mechanism involves the brain’s visual processing center, which becomes overly excitable when confronted with rapid, repetitive visual input. The visual cortex, located in the back of the brain, is unable to process the constant, alternating stimulus in a normal, controlled manner. This overload disrupts the delicate balance between excitatory and inhibitory signals.
When this occurs, the brain may exhibit a Photoparoxysmal Response (PPR), which is an abnormal electrical discharge recorded on an electroencephalogram (EEG). The PPR is characterized by spikes, sharp waves, or generalized epileptiform discharges that begin in the visual cortex and can spread to other areas of the brain. This heightened excitability and synchronous, abnormal firing of neurons culminates in a seizure.
The abnormal waveform produced during a PPR is nearly identical to the electrical activity seen in spontaneous seizures. The degree to which the PPR spreads from the visual cortex to other brain regions is often associated with the likelihood of a clinical seizure occurring. This neurological phenomenon is a genetically determined trait that indicates an increased risk for generalized epilepsy.
Key Characteristics of Dangerous Light Patterns
The risk posed by flashing lights is directly related to the specific physical properties of the light source. The most significant factor is the flash rate, measured in Hertz (Hz), which represents the number of flashes per second. The frequency range most likely to trigger a seizure falls between 3 and 60 Hz, with the peak danger zone typically between 15 and 25 flashes per second.
Strobe lighting operating within this optimal range can induce a seizure in a susceptible individual. High light intensity and a high contrast between the light and dark periods significantly increase the risk. Lights that fill a large portion of the visual field, such as those in a large performance venue or a full-screen video effect, are also more provocative.
Certain colors are more stimulating than others, with rapidly alternating red and blue flashes being particularly problematic. Exposure to contrasting geometric patterns, such as bold black and white stripes or checkerboards, can also act as triggers, even if they are stationary. These characteristics combine to maximize the visual cortex overload, pushing the brain past its threshold for a normal response.
Practical Safety Measures
For individuals who are photosensitive, managing exposure involves several practical steps. If a flashing light source suddenly appears, the most effective first action is to immediately cover one eye and turn away from the stimulus. Covering only one eye reduces the total amount of visual input reaching the brain and can interrupt the process that leads to a PPR.
Preventative measures involve managing screen use, as digital displays can be a common source of flicker and patterns. It is advisable to sit far back from a television or computer screen and to watch in a well-lit room to reduce the contrast between the screen and the surrounding environment. Some individuals may benefit from wearing specialized glasses, such as those with polarized or blue-tinted lenses, which filter out certain wavelengths and reduce glare.
These filters cannot eliminate photosensitivity entirely, but they can help to mitigate the effects of the visual stimulus. Taking regular breaks from screens and avoiding known situations where intense strobe lights are used, such as certain clubs or concerts, are straightforward ways to reduce the risk.