Try dancing left and right (or whatever) in a light source right in front of him.
He won't see you.
He will spot you only when you move within 20m of him. And something tells me only because he will hear a sound of your footsteps.

As a player you can easily tell an enemy from a friendly when he's lit by those lamps. This creates an unfair advantage for humans.

The night itself isn't that dark either. AI should at least be able to spot your silhouette moving around in the dark.

Fixing this not only will make AI reactions more humanlike, it will also create the ability to make true stealth missions, where light sources and movement speeds make a difference.