The experience of feeling “weird” around flashing or flickering lights is a common phenomenon known as visual photosensitivity, representing a measurable physiological reaction within the nervous system. This response indicates that the brain is struggling to process the rapid changes in visual input, which can lead to uncomfortable sensations. This sensitivity is a direct result of how the visual cortex processes temporal changes in light intensity. Understanding this disruption explains why certain light sources, like older fluorescent bulbs or some electronic screens, are particularly bothersome.
The Science of Visual Flicker
The root of visual discomfort from flickering light lies in the brain’s ability to process rapid sequences of visual information. Most light sources, such as AC-powered bulbs or refreshed screens, are essentially flashing. The brain has a limit to how fast it can register individual flashes, known as the critical flicker fusion frequency (CFF). For most people, the CFF is between 50 and 90 Hertz (Hz), or flashes per second. When the frequency is below the CFF, we perceive a distinct, disruptive flicker.
Flicker just below this threshold is often the most irritating because the visual system strains to resolve the rapidly changing stimulus. Frequencies above 100 Hz are perceived as steady, or “fused,” by the brain. However, even subliminal flicker, just below conscious detection, can still produce visual fatigue and cortical arousal in the central nervous system. The temporal resolution of the visual system is highly individual, meaning what one person perceives as steady, another may see as a source of strain.
Common Non-Seizure Responses
For the majority of people, the “weird feeling” is symptoms caused by the brain’s overexertion responding to disruptive light input. One frequent complaint is asthenopia, or visual discomfort, including eye strain, blurred vision, and difficulty focusing. This struggle to stabilize the visual field burdens the eye muscles and visual processing centers. Flickering lights also trigger headaches and migraines in susceptible individuals. Photophobia, or light sensitivity, is a common feature of migraine, and flicker can initiate a painful attack.
Exposure to low-frequency flickering lights (1 to 20 Hz) can cause disorientation called flicker vertigo. This effect, also known as the Bucha effect, creates a temporary imbalance in brain-cell activity that induces nausea and spatial disorientation. Flicker vertigo is not limited to those with a history of epilepsy and can be triggered by scenarios like sunlight filtering through tree leaves or a rotating helicopter blade. Symptoms include rapid blinking and loss of fine motor control, which usually subside quickly once the light source is removed.
The Link to Photosensitive Epilepsy
The most serious reaction to flashing lights is photosensitive epilepsy (PSE), where visual stimuli can trigger a seizure. PSE is rare, affecting about 3% to 5% of all people with epilepsy, or approximately 1 in 4,000 people. This condition is most common in children and adolescents, and sensitivity often decreases with age. The visual triggers for PSE involve lights that flash or patterns that alternate at specific frequencies.
The common range for triggering seizures is between 3 and 60 Hz, with the highest risk between 15 and 25 flashes per second. Triggers include intense strobe lights, specific video game sequences, and flicker from older television screens. Seizures are more likely to be triggered by stimuli that are bright, have high luminance contrast, and fill a large portion of the visual field. If flashing lights cause loss of consciousness, convulsions, or other symptoms suggesting an epileptic event, seek immediate medical consultation. Feeling disoriented or unwell from flicker does not automatically mean a person has photosensitive epilepsy.
Strategies for Minimizing Exposure
Minimizing the impact of flickering lights involves avoiding triggers and adjusting environmental light sources. For computer users, increasing the monitor’s refresh rate to at least 75 Hz reduces screen flicker and visual fatigue. Selecting displays that use direct current (DC) dimming instead of pulse-width modulation (PWM) dimming eliminates flicker in many modern LED screens. Reducing glare and contrast on screens also helps lessen visual strain. This is achieved by using anti-glare filters, positioning the monitor away from direct windows, and adjusting contrast levels.
When encountering an unavoidable flicker source, such as a faulty fluorescent bulb or a strobe light, look away or quickly cover one eye. Keeping one eye closed reduces the intensity of the visual input, which can sometimes prevent a photosensitive reaction. Wearing tinted glasses may also help filter out light wavelengths that contribute to discomfort. Replacing flickering fluorescent bulbs with flicker-free LED alternatives can make a significant difference in daily comfort.