Earlier quoted context omitted.
That doesn't help if you're in dim lighting or have vision problems.
That's why the dollar coin was redesigned in 2000. The old dollar coin had a reeded edge that was too similar to a quarter, so it was sometimes hard to distinguish if you had vision issues (or if you didn't have vision issues because they were about the same size as a quarter). The new ones have a smooth edge so you can tell them apart from quarters without having to look at them
At least that's how it seems to me. It's an interesting design issue. I don't personally care too much -- I'm fine with the paper bill -- but I do have curiosity about why the coin designers have made the decisions they did about the $1 coin.