Derivative light and the strength of its illumination
Weaker light and thinner ray-angles illuminate a struck place less
A single large shaded triangle occupies the page, showing a small luminous body, a larger shadowy body, and the broad shadow they cast, labelled a b c d e and f g h m. Two short propositions state that a derivative (secondary) light illuminates a struck place less than the original light in proportion to its diminished brightness, and that a pyramid of rays lights the place it strikes the less the thinner its angles. The leaf continues the notebook's study of how illumination weakens as it spreads.
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Derivative light illuminates less than the original
By as much as a derivative light is of lesser brightness than the original light, by so much less will its pyramids of rays illuminate the place they strike.
Thinner ray-angles give weaker illumination
The pyramids of rays illuminate the place they strike so much the less as their angles are thinner. The figure of a small luminous body, a large shadowy body and a large shadow shows this diminishing light across a b c d e and f g h m.