Taking a train to Boston, I was sitting next to the window and closed my eyes for a nap. It was a sunny day, and as the train moved forward, shadows of nearby objects would periodically interrupt the light's path from the sun to my eyes. The result was a rapid (about 10 Hz), aperiodic, change from bright illumination to relative darkness, or a strobe effect. I noticed that this led to a subtle generation of a visible image, which had strange washed out colors and what could be called psychedelic geometry. This effect was persistent, and seemingly not subject to conscious control. To explore the effect further, I built a bright strobe light that could be placed in front of the closed eyes.
The WS2812B LEDs are individually addressable, meaning the Teensy LC can set each LED to a specific color, using only one output pin for the data. The program at start-up flashes each LED in sequence over a few seconds, which gives a period of time during which a low current is drawn, so that it is possible to reprogram the microcontroller through USB without drawing excessive current from the USB port. In normal use the project is powered from a 5 V USB charger, which is capable of supplying the higher current when all LEDs turn on at once. After the start-up period, the LEDs are all turned on and off simultaneously every 50 ms to generate a 10 Hz strobe. The very simple code, based on a FastLED library example, can be downloaded here.
The LED rings are glued inside the frame of old welding goggles, making something that looks like a sci-fi movie prop. When placed so close to the eyes, the light from the LEDs is bright, as intended to simulate sunlight. With the eyes closed, the brightness is tolerable, similar to being outside on a sunny day.
External view of the welding goggles with LEDs.
Internal view.
Using this strobe light, I was able to replicate the effect I experienced on the train ride. There do not seem to be any precise requirements to achieve the effect - as long as the strobe is bright, around 0.5 x duty cycle, uniformly illuminating the eyes, and flashing around 10 times per second, the subtle mental images are generated. If there is not a clear image to compete with the uniform illumination of the strobe, the mental images may even be seen with eyes open. The images are abstract geometric, ranging from simple to complex, mostly linear, and formed of washed-out and subtle colors which do not really map to normal color terms. Perhaps these are composed of "pure edges" and the colors are only apparent. The images evolve over time and seem to depend on the history of what was seen before the strobe light was started. My hypothesis is that the strobe light's uniform illumination of the retina combined with rapid shifting from dark to bright causes large-scale activation of the visual processors in the eye and brain. Because these processors are designed to discriminate between different appearances, while the strobe illumination is uniform, they are driven towards some stochastic state, in a similar manner as the static on a radio tuned to a non-broadcast wavelength. Normally we do not experience these states because the brain knows that "there is nothing visible" and automatically shuts off the information pathway. However the periodic strobing overrides this, because such a rapid change in light level implies "there is something visible", so these static-like states enter the visual experience. Generally upon starting the strobe, I see 5 to 7 lines that are asymmetrically arranged passing through a central point, then orbs appear around this central point between the lines, then staircase patterns and other linear geometries evolve over tens of seconds. I think it would be fair to call this psychedelic geometry, and I imagine that the states experienced under the effect of psychedelic chemicals originate in a similar manner.
So far it may sound rather appealing - having a psychedelic experience with just a strobe light - why isn't everyone doing this? There are a few caveats. The image for me is barely present, it is very subtle, and not really anything like what I see with the eyes open, it is more an abstract idea of a pattern. The colors are nondescript and blend into one another. The repertoire of patterns seems rather limited and faint. Most detrimentally, there is a constant feeling of visual fatigue, since the visual processing pathways are being over-stimulated and are not sure how to respond - if you have any predisposition to seizures, using this strobe light may well initiate one due to the constant activation of the optical nerve and associated systems. Overall it is not an enjoyable experience, and after trying a few times with the same result I do not see any reason to continue using the strobe goggles.