Is it "longer" really, or is that just dependant on light positioning? In this case there are two lights, one from the right, and another from the left. If two lights are both equidistant from the object, and the line between the two lights passes in the center of the object, the gradation to the core shadow is the same between the two lights. in this case, I believe it's due to light positioning

Hi @Avşin, I think it's because that, on the light side, there is more room to gradate; you go from dark to a light value. On the shadow side you're only going from dark to a mid value. In the 3D model, the gradation seems to be at the same speed, it's just that the left side stops gradating sooner, once it has reached the mid value. Also keep in mind that you're using a digital 3D-model. You might find reality to behave slightly different. If you're curious, study a white cylindircal object in real life (like a toilet paper roll, or the cardboard part of a toilet paper roll wrapped in a sheet of drawing paper). Hope this helps :)

Because the value changes on the curved surface are not linear. Look at that lesson by Dorian Iten: https://www.youtube.com/watch?v=6vapw6n6FyU&list=PLO5emhHKYxgXNqOlHTHKiQPkLf8tDodgJ&index=19