Science · 6 pages · 12 min
Why some shadows are sharp and some are soft
A shadow goes sharp or soft according to the size of the lamp and the gap to the wall.
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From the opening
A shadow is the place a blocking object keeps the light from reaching. The edge looks sharp or soft because of how big the source is and how far the object stands from the surface, not because the object is more or less solid. The opening covers why a small lamp looks hard, how distance widens the blur, and what the Sun's disk changes.
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Inside
- Why a small lamp looks hard
- How distance widens the blur
- What the Sun's disk changes
- Why overcast light casts little
- Where the idea stops applying
- A distinction worth keeping
Sources
- Umbra and penumbra in geometric optics
- The Sun as an extended source