Scattering Of Light

[bluedaydream]

I had a question. A friend of mine noticed yesterday that the shadows formed by leaves on the ground are fuzzy little circles/ ovals. I was wondering why that is. How come the shape of the leaf is not even vaguely defined when its shadow is casted on a surface? Does anyone know? I would imagine it has to do with light scattering.

[swansont]

Diffraction is the most likely culprit. Light bends a little when it goes around a sharp corner, and this fuzzes the shadow out.

[insane_alien]

it also has to do with the fact that the sun is not a point source of light. a shadow will be sharply defined when the leave is close to the ground but less defined when further away.

 

it all adds up.

[iNow]

In addition to the above, the shape of the shadow would also be more defined if the leaf was closer to the ground. The higher up (farther from the ground) the leaf is, the more distance light has to interfere and make the outline "fuzzy" before reaching the ground.

[swansont]

In addition to the above, the shape of the shadow would also be more defined if the leaf was closer to the ground. The higher up (farther from the ground) the leaf is, the more distance light has to interfere and make the outline "fuzzy" before reaching the ground.

 

I agree with everything but the use of "interfere," which has a specific definition that isn't in play here. The extended source and diffraction effects certainly increase with distance.

[iNow]

I agree with everything but the use of "interfere," which has a specific definition that isn't in play here. The extended source and diffraction effects certainly increase with distance.

 

I was questioning my choice of that word. Thanks for clarifying.

[thedarkshade]

Light bends a little when it goes around a sharp corner.

And as the others said, the shadow with the true shape of the leaf will be if the leaf is on the ground, and the shadow will continue fuzz if the leaf is above the ground. This is because as light bends near sharp edges and that bend will go on and will be more apparent if the distance of the leaf (in this case) from the ground is higher, making so the shadow of the leaf less like the true form of the leaf.