Question

why some shadow are sharper some other diffused short answer types ​

Answer 1

As we can see, only point light creates a sharp, easily defined shadow. When the light source is bigger (more scattered), the shadow gains a blurry, gradient edge. The phenomenon I've just explained is responsible for supposedly multiple shadows coming from a single light source too.

Answer 2

Answer:

the distance between the light source and the object, the distance between the object and the shadow, and the size of the light source would all have an effect these are are factor that effect sharpness and blurriness of a shadow.