Originally Posted by
Radioman
If a door is suddenly opened and you get a bright light, it can take a good few seconds for your eyes to readjust.
There's the issue of adjusting to the sudden light, and then adjusting back to the dark - and adjusting to dark takes rather more than a few seconds. Fully adjusting to darkness can take up to 30 minutes. See page 23 of
this report for better details.