Question

why is that so that a needle does not form a shadow on wall when the bulb is placed near it​

Answer 1

Answer:

1 Light bends around very small objects. This can be very easily observed if you place a pencil tip close to your eyes. You will see it for a while but as you bring it closer it becomes invisible.

2 Light reflects. Due to this, the scattered light from the bulb is not able to cast a shadow. The shadow is very small and is overpowered by reflected light. This is not true for larger objects.

3 Shadow is always there but not visible. Well, this is a continuation of the 2nd point so very self-explanatory.