There was a recent thread about tail lights and their brightness, and several posters insisted that they are nearly impossible to see in daylight -- and that, to have any hope, a person must run a super-bright tail light -- I think one poster was talking about 300 or 350 lumen lights. The argument was rather tame by bf standards, but there was some dispute.
Today I was out riding a regular route. It's only mid-spring, so not super-sunny yet, but it was (for April, anyway) full sun. A vehicle pulled alongside me with the passenger window down, and I thought the driver said "I like your bike!" I thought it rather surprising that an elderly lady appreciated my custom Gunnar gravel bike.
But then I realized she was saying "I like your light!" I stopped, and we chatted for a bit. She said she could see the light long before she even could tell that it was attached to a bicycle.
What's the light? An old Cygolite that I've had for five years. 100 lumens.
The really cool thing was connecting with a driver who lives along one of my regular routes. I like having friends out there -- you never know when you'll need one.