Why is the light cutoff so bad?

[filibis (Emir Sinan Gürlek)]

This looks like terminator effect to me. It happens with low-poly objects in Cycles. Check this topic:

Is there a workaround for the terminator problem?

You know, the issue where the shadows on low poly objects look like garbage and are distorted by the geometry despite smooth shading? [https://blenderartists.org/forum/attachment.php?attachmentid=298252&d=1395762708] Trying to do low poly stuff in cycles is a big “NO”. Just wondering if there is a workaround and if there are plans to improve/fix this (I know it’s not considered a bug) problem?

In order to solve terminator effect you need to either increase polygon count or size of light (or both) (or use Eevee which doesn’t have this issue).