Myth: Nightsight has no effect

Is this true? I have NEVER known this to have an effect but I am not sure I know what to look for.

Nightsight has an effect. There was one point like 2 years ago where I forgot to put it up, and I couldn't squint or glance or something at nighttime while out in the mountains. I put it up and it worked.

In that case..

I forget if it still can be used to get into a certain section in the seren arena, but at one stage you could use it instead of the torches. Though then you couldn't get out because there's no actual exit