A shadow's edges grow blurrier as the light source becomes larger or moves farther away.

The longer version

Every point on an extended lamp throws its own shadow, and the overlapping copies do not line up perfectly. Where several copies coincide the shadow is darkest; toward the rim only some overlap, producing a gradual fade rather than a crisp boundary.

A small distant bulb approximates a point source and gives hard edges; an overcast sky is the extreme opposite and erases outlines almost entirely. Photographers exploit this by adding diffusers that enlarge the effective source. During a solar eclipse, the sun's size is what softens the edges of the moon's shadow on the ground.

Where this entry sits

These facts explore how light behaves and how human eyes turn it into the colors we see. Along the way you meet rainbows, prisms, mirrors, shadows, lasers, and optical tricks that fool our vision every day. The full list sits on the Color and Light page, where every entry is listed in order.