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OBJECTS AND INSTRUMENTS96
Light and Illusions
SEEING IS MIRACULOUS. U p s i d e - d o w n patterns of light on The outermost edge of our vision, less developed than the
our retinas, transmitted to the brain as chains of electrical center, reads only movement and can often make mistakes.
impulses, are translated into a world of space, atmosphere, Someone passes our open door, perhaps; we turn our head
form, and movement. To interpret visual stimulus, our but no one was there. The slightest recognition is instantly
brains search for nameable things, and are quick to matched to our wealth of experience and expectation, and
propose ideas. We will even see things that do not exist we can be fooled. Here we look briefly at our perception of
because minimal information suggests they are likely to be light and darkness and our interpretation of diagrammatic
there. We only need small prompts; hence our recognition illusions. Through these we can enjoy witnessing our own
of a cartoon face composed of three lines, and our ability deception and bafflement and understand certain factors
to see forms in clouds or fire. that are very useful in picture-making.
LIGHT AND SHADOW with what you see? Does the light enhance the subject? Could
you alter and improve it? On pp.102-03 deep shadows cast across
W e learn to read light and shadow in our environment as shells make their form easier to perceive. Below, a lit photograph
indicators of solidity and depth of space. Artists emulate and of an egg shows essential points to observe in tonal drawing.
manipulate this effect in their pictures. Before starting a tonal
drawing of any subject, think about its illumination. Are you happy
The egg's darkest region is seen The egg's lightest region is seen
against a lighter background. against a darker background. Run
The two tones meet without your eye around the circumference
a division or outline between. of the egg. See how its "edge"
smoothly changes from light
The bottom-left quarter of the egg against dark to dark against light.
lightens slightly toward its "edge"
when seen against the darker Below the bottom "edge" of the
shadow cast on the paper. The rim egg there is a rim of light reflected
of light on the egg is reflected light onto the paper by the underside
received from surrounding paper. of the egg.
Gray squares Card experiment
The perceived tone of a black white, To further examine changes in tone,
gray, or colored surface is never try this experiment. On acloudyday,
constant. Three factors change it:
the amount of light it receives; the cho
adjustment of our eyes (in growing can
accustomed to a level of light); and cards the same size, one blackandone
the proximity of contrasting tones. white. Tape them to the glass. From
Here, two identical mid-gray squares across the room both will appear
are seen against black and paler gray gra
squares. The small squares are black card and fold and retapeitwith
identical in tone, but do not appear half sticking out. Adjust the angleofthe
so. We perceive one to be lighter protruding part and again stepback.At
than theother.This effect is caused one point you will catchenoughlight
by the contrast of their surroundings. on
lighter than the white one.
