Like, how to unlock it? If that's what you mean, you'd either need to get through the story once, or experience the bad sun event for the first time. I am unsure which, but it will be one of those, if not both.
Oh. Then I am unaware, unfortunately. Sounds like it might be a bug, but I would make sure, first. If you're SURE that it is never dealing damage to you, I would report the bug within the pinned bug report thread.
Did you equip the Welder's Mask at the hole? If so, I think that mask makes you not take damage from the sun. Make sense, if you consider the requirements for surviving SCP-001 "When Day Breaks", as people had to shield their eyes from the sun.
