Rays Around a Light Are Made in the Eye; the Finger Test
Three images from a luminous body, convex-mirror reflection, and blocking the rays with a finger
Under the heading that the rays seen around a bright light when the lids are narrowed are generated in the eye and nowhere else, Leonardo compares the eye to a convex mirror: such a mirror (p, lit by q) shows the image of the light to all the surroundings n m o that see it. He then states that the luminous body sends three images to the eye, one straight to the pupil and two that break on the convex lids and rebound to form the ray-like splendour when the eye is narrowed as if aiming at a target. A finger experiment proves it: raising a finger crosswise to meet the bottom of the light makes the upper rays vanish at once, and lowering it to the top of the light makes the lower rays disappear.
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Rays around a light are generated in the eye, not outside
Leonardo's heading states that the rays seen around a luminous body when the lids are narrowed are generated in the eye and nowhere else. The luminous body sends three images, of which one goes straight to the pupil; the other two break on the convexity of the lids and rebound to the opposite rims, joining above and below the first image as a splendour stamped by the lids in the shape of rays.
The finger test: blocking one edge of the light kills its rays
With the eye narrowed, two gatherings of rays appear around the distant light, one above and one below. Raise a finger crosswise from below to meet the origin of the light and all the upper rays vanish at once; lower it from above to meet the top of the light and all the lower rays disappear.
A convex mirror shows the light to all who see it
Convex mirrors reflect the rays received from a luminous body into all places that see the mirror where the luminous body sees it. With q the luminous body and p the convex mirror, the whole surrounding circuit n m o that sees the mirror can see the image of the light in it.