Why isn’t a shadow as sharp as one can see the object?
In: Physics
if you and your toxic 5 yr old buddies are playing call of duty and someone pops up right in front of you point blank your group starts shooting everywhere, the missed bullets from this crossfire go many directions and end up on some wall far away.
later on in the game your group spots an enemy in the distance with a wall right behind him. your group opens fire. the missed bullets from this crossfire are very concentrated on the wall behind the enemy.
your group is the light source
bullets are the photons
enemy is the object
bullethole concentration is the sharpness of the shadow
light comes from everywhere (reflected all around us). even if you have a single point of light, the light is going to bounce around a lot.
the closer an object is to something, more of that reflected light will be blocked.
the more light is blocked, the clearer the shadow will be
Imagine you have two point source lights that are near each other. A surface that’s exposed to both lights will be illuminated twice as brightly as a surface that’s only exposed to one.
Now, put an object between the light and the surface. Because there are two lights, the object actually casts two shadows. But, if the object is very close to the surface, the two shadows will be close to each other, even overlapping. As you move the object away from the surface, the two shadows get farther apart.
Where the two shadows overlap, you get a dark shadow. Where there’s only one shadow, you get a light shadow.
Now, the thing to realize is that no real light source is a single point. It takes up space, which looks the same as multiple light sources very close to each other.
So, in summary, the fuzzy border of the shadow is the region where only part of the light source is visible.
Imagine a long narrow triangle. Right near the “point”, the two sides are next to each other, but down by the “base” the two sides are much further apart, right?
That’s what’s happening. The object itself is the “point” of the triangle, the shadow is the “base”, and light streaming past the object is lots and lots of sides. When the object is closer to the shadow, the light doesn’t spread as much, but when the object is farther away the light spreads out a lot more before hitting the surface that the shadow is on.
Because light isn’t coherent through the atmosphere, it’s diffuse. It bounces off all the objects in the world and comes at us from every direction. The further the object is from the shadow, the more of this diffuse light can lighten the shadow by reflecting off the object on which the shadow is projected.
Its because of a phenomenon called tyndall effect it basically means scattering of light . When light hits the particles on its path it scatters , when the the object that casts the shadow is closer to the wall then the scattering is lower and a sharper image is obtained.
It is the same reason why there is no sunlight in the vaccum of space as there are no particles for light to bounce off.
This will answer all your light-related questions:
https://ciechanow.ski/lights-and-shadows/
Look, I know it’s not the shortest article, but it’s full of 3D animations and the likes, making it SUPER intuitive to understand all about light.
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