One could argue that it’s both chemical and electrical as both are involved in the process of vision.
On a cellular and chemical level, we have photosensitive pigments in our rods and cones which are built from proteins (opsins) and chromophores. Light induces a conformational change in the protein which, through a number of steps, triggers an electrical impulse that travels toward the inner retina, along the nerve fiber layer, and out of the eye via the optic nerve.
During this conformational change, the “activated” photoreceptor is rendered unable to absorb more light until the pigment has, for lack of a better word, regenerated. The time this takes to happen is the time you refer to as “inert”.
