The ephemeral impression or afterimage that we experience after looking at a bright light is known as a "retinal afterimage." It occurs due to the way our eyes and visual system process light.
When we look at a bright light source, such as a light bulb or the sun, the intense light stimulates the photoreceptor cells in our eyes, specifically the cones responsible for color vision. These cells become temporarily overstimulated, and their response takes a brief moment to return to baseline levels.
Once we shift our gaze away from the bright light, the cones that were intensely stimulated become less active, while the surrounding cones that were less affected by the bright light continue to respond normally. This creates a temporary imbalance in the activity of the cone cells.
The result of this imbalance is the perception of an afterimage, where we see a ghostly, inverted image of the bright light or its complementary color. The exact appearance of the afterimage depends on various factors, including the intensity and duration of the original light stimulus and the characteristics of the visual system.
The phenomenon of retinal afterimages is related to the adaptation and response properties of our visual system. Our eyes constantly adjust their sensitivity to different levels of light to optimize vision in varying environments. When exposed to a bright light, this adaptation process takes some time to restore the optimal sensitivity, and the residual activity of the stimulated photoreceptor cells leads to the perception of an afterimage.
It's worth noting that the duration of afterimages can vary from person to person and can be influenced by factors such as the intensity of the original light source, the duration of exposure, and individual differences in visual sensitivity and adaptation.