Although their meanings are opposite, there are times when it is unclear which one to use and cases where both could be used. In your examples, they appear more to be contrasts to me, so but would be my choice, though that doesn't make and wrong. In the first, if talking about the reactions of the eyes to light, then I'd use but, yet which would you use if talking about a process that involved bright lights followed by dark- I think I'd use and.
The best help I can offer is to say that we can have the same troubles. One example I saw a while ago was this:
You can eat now and you can eat later.
Does this mean that you can eat twice or have two opportunties to eat one meal? If the latter, or would make it clearer, but many native speakers would use and there.