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Why can pressing on a closed eye produce a bright spot called a phosphene?

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Compound eye — Senses Vespid wasps (Vespidae), similar to other insects, have compound eyes that consist of thousands of tiny optical units known as ommatidia, which contain light-sensitive photoreceptor cells.

Pressing on a closed eye produces a bright spot, known as a phosphene, because of how the human eye and visual system process sensory input.

While the eye is designed to convert light into electrical signals, the cells of the retina are not exclusively sensitive to light; they can also be stimulated by mechanical pressure. When you press on your eyelid, the physical force stimulates these retinal cells or the neurons in the visual system directly. Because the brain interprets any signal coming from the optic nerve as visual information, it perceives this mechanical stimulation as an impression of light, even though no actual light has entered the eye.1

This phenomenon demonstrates that our perception of light is a result of the activation of the visual pathway rather than the presence of light itself.1