Graded light along the penumbra of a large light source
Brighter reflection has shorter rays; a large light mixes shade and light; the penumbra a-g divided into fractions.
The note holds that a reflection is brighter where its reflected rays are shorter. A large luminous body set behind obstacles shows that the greater the light, the more its shadowy and luminous rays mingle at the impact. In the main diagram Leonardo grades the penumbra: from point m, which sees the whole light a g, through n, o, p, q, r seeing five sixths, two thirds, a half, a third and a sixth of it, down to S where the real, simple shadow begins.
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Brighter reflection where the reflected rays are shorter
That part of a reflection will be brighter whose rays of reflection are shorter. Nearer reflecting surfaces return light more strongly.
A larger light mixes shadowy and luminous rays
The larger the luminous body, the more the convergence of shadowy and luminous rays is mingled together. Where more luminous rays gather there is more light, and where fewer, less; so the shadowy rays come to intermix, softening the boundary.
The penumbra a-g divided into fractions of light
Point m sees and is seen by the whole luminous body a g and holds the primacy of light; n sees a f, five sixths of the light; o sees a e, two thirds; p sees a d, half; q sees a c, a third; r is seen by a b, a sixth; and at S, seeing the end of the light, the real and simple shadow begins. The narrower these pyramid-points, the smaller their base and the less light they make at equal distance.
Darkness conforms to its origin between flat surfaces
The darkness made at the impact of the shadow's convergence conforms to its origin when it is born and ended between near, flat surfaces of equal quality set in direct opposition. The upper figure shows a luminous pyramid interrupted by thin obstacles.