It happens to me at night because not only does it have to be quite dark, I audio need to be dork dark adapted. Your pupil is part of your dark adaption and widens in a mater of seconds. However, your receptors also get doped with rhodopsin, which takes up to 20 minutes to full replenish (blue/uv light bleachers rhodopsin). It’s like being able to lower the F-stop on a camera like normal, but taking 20 minutes to raise the ISO