The flashes, swirls, and pinpricks of light you see with your eyes closed are called phosphenes, and they happen because your visual system is never truly off. Even in complete darkness with your lids shut, your retina generates low-level electrical signals, your brain’s visual cortex hums with spontaneous activity, and mechanical pressure on the eyeball can trick photoreceptors into firing. Most of the time, these closed-eye light shows are harmless background noise from a visual system that evolved to be exquisitely sensitive. Occasionally, though, they point to something that deserves medical attention.
Your Retina Never Fully Shuts Off
One of the more surprising facts about human vision is that the light-sensing cells in your retina fire even when no light reaches them. Researchers have long studied what is called “dark noise,” the random electrical signals that photoreceptor cells produce spontaneously. Rod cells, the ones responsible for low-light vision, generate intermittent current deflections that look almost identical to the signal produced when an actual photon of light hits the cell. Molecular experiments have confirmed that this discrete noise comes from rhodopsin, the light-sensitive protein in rods, spontaneously activating on its own without any light stimulus.1PubMed Central. Origin of Discrete and Continuous Dark Noise in Rod Photoreceptors
Your brain has to deal with these false signals constantly. Most of the time, it filters them out so you do not perceive them as light. But when you close your eyes and settle into a dark, quiet environment, you strip away the flood of real visual information that normally drowns out the noise. The faint sparks, drifting blobs of color, and shifting patterns you notice in that stillness are partly the result of your brain losing the competition between real signals and this background static. The visual cortex, suddenly underemployed, begins interpreting stray retinal signals and its own spontaneous neural firing as something to see.
Pressure on the Eyeball
If you have ever rubbed your eyes and seen a burst of light or a kaleidoscope of color, you have experienced mechanical phosphenes. Pressing on the eyeball physically deforms the retina, and photoreceptor cells respond to that mechanical distortion the same way they respond to light: by sending an electrical signal down the optic nerve. The brain does not know the difference, so it interprets the signal as a flash or pattern of light.
You do not have to rub hard. Rolling over onto a pillow that presses against your eye, sneezing forcefully, or even a sudden change in blood pressure during a coughing fit can produce brief flashes. These pressure-induced phosphenes are generally harmless and disappear as soon as the force is removed. They are one of the most common and least worrying explanations for closed-eye light experiences.
When Flashes Signal an Eye Problem
Not all closed-eye flashes are benign. One of the most important causes to know about is posterior vitreous detachment, an age-related condition in which the gel-like substance filling the eyeball (the vitreous) shrinks and peels away from the retina. This is common as people age, and when it happens, it can tug on the retina and trigger flashes of light called photopsia, along with new floaters drifting across your field of vision.2PubMed Central. Spontaneous posterior vitreous detachment: A glance at the current literature
Most posterior vitreous detachments resolve without causing permanent harm. The concern is that in some cases, the pulling force on the retina can create a tear, and a retinal tear can progress to a retinal detachment, which is a sight-threatening emergency. The acute onset of new floaters and flashes is one of the classic warning signs that an eye doctor will want to evaluate urgently.3JAMA. Acute-onset floaters and flashes and risk for retinal detachment If you suddenly start seeing repeated flashes of light, especially if they are accompanied by a shower of new floaters or a shadow creeping across part of your vision, that warrants a same-day or next-day dilated eye exam rather than a wait-and-see approach.
A useful rule of thumb: phosphenes that you have noticed for years and that show up mainly when you are relaxing in the dark are almost certainly harmless. Phosphenes that are new, sudden, persistent, or accompanied by other visual changes deserve professional evaluation.
Migraine Aura and the Visual Cortex
Migraine with aura is one of the best-understood neurological causes of seeing lights with your eyes closed. Roughly a quarter to a third of people who get migraines experience aura, and the visual form is by far the most common type. The hallmark is a slowly expanding arc or zigzag pattern, often shimmering or flickering, that typically builds over five to thirty minutes before fading.
The mechanism behind this is a phenomenon called cortical spreading depression, a slow wave of intense electrical activity followed by a period of suppressed activity that rolls across the surface of the brain. Functional MRI studies have directly observed this wave moving across the visual cortex at roughly 3 to 4 millimeters per minute, time-locked to the visual disturbance that subjects reported seeing.4PubMed. Mechanisms of migraine aura revealed by functional MRI in human visual cortex The slow speed of the wave explains why aura patterns crawl gradually across your visual field rather than flashing all at once.5PubMed Central. Role of cortical spreading depression in the pathophysiology of migraine
What makes migraine aura distinct from ordinary phosphenes is its structured, progressive nature. Instead of random sparks or blobs, people describe geometric patterns, fortification spectra that look like the crenellations of a castle wall, or expanding crescents of shimmering light. Computational models have linked these specific geometric shapes to the way cortical spreading depression interacts with the organized architecture of the visual cortex.6PubMed Central. Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence You can see migraine aura with your eyes open or closed, because the disturbance originates in the brain rather than the eye.
Optic Neuritis and Visual Snow
Some neurological conditions produce phosphenes through different pathways. In optic neuritis, inflammation of the optic nerve can cause flashes of light triggered by eye movement. These movement phosphenes are distinct from the harmless sparks healthy people see; they share characteristics with a phenomenon called Lhermitte’s sign, in which nerve demyelination causes abnormal electrical discharges in response to mechanical stimulation. Optic neuritis is sometimes an early sign of multiple sclerosis, so movement-triggered phosphenes that do not go away are worth mentioning to a doctor.7PubMed. Movement phosphenes in optic neuritis: a new clinical sign
Visual snow syndrome is a separate and less well-known condition in which people see a constant overlay of tiny flickering dots across their entire visual field, somewhat like television static. The dots are visible whether the eyes are open or closed. Brain imaging of people with visual snow syndrome has revealed increased metabolic activity in areas of the visual cortex, particularly the lingual gyrus and cuneus, with a peak increase of about 24% compared to healthy controls.8PubMed Central. Simultaneous 18F-FDG PET/MR metabolic and structural changes in visual snow syndrome and diagnostic use The condition appears to involve a visual cortex that is persistently overexcitable, generating perceptions of light and movement where there is none. Visual snow is chronic and, at present, difficult to treat, but it is not dangerous and does not lead to vision loss.
Sensory Deprivation and the Brain Filling In
Your brain does not handle sensory boredom well. When visual input drops to zero or near-zero, the visual cortex begins generating its own content. This has been demonstrated experimentally using a technique called Ganzfeld stimulation, in which subjects stare into a completely uniform, featureless field of light (or darkness). Within minutes, many people begin to see hallucinations ranging from simple colored blobs to more complex patterns. Research comparing uniform-field conditions with flickering-field conditions found that simple hallucinations were more common than complex ones in both setups, and that flickering light amplified the effect, probably by heightening the excitability of the visual cortex through bottom-up input.9PubMed Central. Visual hallucinations induced by Ganzflicker and Ganzfeld differ in frequency, complexity, and content
This same principle helps explain why lying in a dark room with your eyes closed at bedtime is prime time for noticing phosphenes. You have eliminated competing visual input, you are relaxed, and your visual cortex starts riffing on whatever signals it can find, whether that is retinal dark noise, spontaneous cortical activity, or some combination. The patterns people report in these situations, swirling colors, drifting shapes, faint geometric grids, are strikingly consistent across individuals, suggesting a shared neural architecture rather than pure imagination.
Meditation practitioners have long reported similar experiences. A study cataloging light experiences during meditation classified them into discrete lightforms and diffuse or patterned lights, and found strong parallels with phenomena documented in sensory deprivation research. Practices that deliberately minimize sensory input and emphasize focused attention appear to produce perceptual outcomes quite similar to those seen in formal deprivation experiments.10PubMed Central. A phenomenology of meditation-induced light experiences: traditional buddhist and neurobiological perspectives The closed-eye visions reported by meditators are not mystical artifacts but a predictable consequence of reducing sensory input to the visual system.
Medications and Substances That Cause Phosphenes
Certain drugs can trigger closed-eye visuals by interfering with retinal or cortical signaling. One well-documented example is ivabradine, a heart-rate-lowering medication used to treat angina. Ivabradine works by blocking a specific type of ion channel in cardiac pacemaker cells, but the same type of channel exists in retinal neurons. By inhibiting these channels in the retina, the drug can produce phosphenes in some patients, typically described as brief flashes or a transient sensation of enhanced brightness.11PubMed Central. Cellular mechanisms underlying the pharmacological induction of phosphenes The effect is generally mild and tends to diminish over time, but it can be startling if you are not expecting it.
At the other end of the pharmacological spectrum, serotonergic psychedelics like psilocybin produce vivid closed-eye visuals through a completely different mechanism. These compounds activate serotonin 2A receptors in the cortex, which dramatically increases spontaneous neural excitation in visual areas. Research has shown that psilocybin disrupts the normal balance between externally driven and internally generated cortical activity, essentially letting spontaneous excitation overwhelm the signals coming from your eyes. Blocking serotonin 2A receptors with a specific antagonist completely prevented these effects, confirming that the receptor is the key gateway.12PubMed Central. Activation of serotonin 2A receptors underlies the psilocybin-induced effects on α oscillations, N170 visual-evoked potentials, and visual hallucinations
Other medications occasionally linked to phosphenes include the erectile dysfunction drug sildenafil (which affects an enzyme also found in retinal cells) and the anti-seizure medication vigabatrin. Digitalis, one of the oldest heart medications, has been known for centuries to cause visual disturbances including colored halos and flashes. If phosphenes start shortly after beginning a new medication, that connection is worth raising with your prescribing doctor.
Cosmic Rays and Light Flashes in Space
One of the stranger chapters in phosphene research comes from astronauts. Since the Apollo missions, space travelers have reported seeing flashes of light with their eyes closed, particularly during periods of darkness. These flashes were eventually traced to high-energy charged particles in cosmic radiation passing through the eye and, possibly, the visual cortex itself.13PubMed Central. Light flashes and other sensory illusions perceived in space travel and on ground, including proton and heavy ion therapies A single cosmic ray particle can deposit enough energy along its path through the retina to trigger a signal in photoreceptor cells, and the brain interprets that signal as a brief streak or point of light.
The same phenomenon has been documented on the ground in patients receiving proton beam or heavy ion radiation therapy for eye or brain tumors. Some patients report seeing flashes during treatment sessions as the therapeutic particles interact with their retinal tissue.14Europe PMC. Mechanisms of phosphenes in irradiated patients This is not a cause of everyday closed-eye lights for people on Earth, where the atmosphere shields us from most cosmic radiation, but it is a vivid demonstration of how sensitive the visual system is. Your retina can detect a single subatomic particle passing through it, and it responds the only way it knows how: by telling your brain it saw light.
Flickering Light and Geometric Patterns
If you have ever noticed structured geometric patterns during closed-eye light experiences, shapes like spirals, honeycombs, concentric rings, or radiating fans, you are seeing something that scientists first described more than two centuries ago. The mathematician and physiologist Jan Purkinje documented geometric phosphenes produced by flickering light in 1819, and they have fascinated researchers ever since.15PLoS Computational Biology. A Model for the Origin and Properties of Flicker-Induced Geometric Phosphenes The patterns are remarkably consistent across people: the same basic catalog of spirals, grids, and tunnels shows up whether the stimulus is flickering light, pressure on the eyes, sensory deprivation, or migraine aura.
The reason for this consistency lies in the architecture of the visual cortex. The primary visual cortex has a very regular, map-like organization where nearby points in visual space are processed by nearby groups of neurons. When a wave of excitation spreads across this organized surface, whether driven by cortical spreading depression, sensory deprivation, or external flicker, the resulting pattern of neural activity maps onto specific geometric shapes in your perceived visual field. Spirals in the cortex become spirals in your vision. A ring of activity in the cortex becomes a ring of light in front of your closed eyes. The geometry is not random; it is a direct readout of the spatial organization of your own brain.
Phosphenes as a Tool in Medical Technology
Researchers have turned the phenomenon of phosphenes from a curiosity into a clinical tool. Transcranial magnetic stimulation of the visual cortex reliably produces phosphenes, and clinicians use the phosphene threshold, the minimum stimulation intensity needed to produce a flash, as a measure of visual cortex excitability. Applying TMS over the occipital cortex produces phosphenes and can also temporarily suppress the ability to see real visual stimuli, demonstrating just how directly artificial stimulation can commandeer the visual processing pipeline.16PubMed Central. Phosphene-guided transcranial magnetic stimulation of occipital but not parietal cortex suppresses stimulus visibility
The most ambitious application of phosphene science is in visual prosthetics for people who have lost their sight. Retinal implants like the Argus II and Alpha AMS use electrode arrays placed on or near the retina to stimulate surviving retinal neurons, producing patterns of phosphenes that the brain learns to interpret as useful visual information. These devices have enabled patients with retinitis pigmentosa to perceive light, detect motion, and recognize large objects.17PubMed Central. Can bionic eyes restore vision? Breakthroughs, challenges, and future frontiers in ophthalmology – A comprehensive review Cortical visual prostheses take the concept further by bypassing the eye entirely and stimulating the visual cortex directly. In both cases, the fundamental unit of restored vision is the phosphene: an artificially evoked perception of light that, with enough resolution and the brain’s remarkable adaptability, begins to resemble sight.
The fact that phosphenes can be generated at every level of the visual pathway, from the photoreceptors to the optic nerve to the cortex itself, is what makes these prosthetics feasible. It also explains why closed-eye light experiences are so varied. A flash from rubbing your eyes originates at the retina. A migraine aura originates in the cortex. A cosmic ray flash originates from a particle passing through any visual tissue in its path. Your brain experiences all of them as light because, from its perspective, a signal arriving from the visual system means one thing: something was seen.