I tend to agree with
Joe Bikerider
I have been using my lights during daytime riding for the last four or five years. Not the super bright lights, but some small Bontrager Flares that I think are only 100 maybe 200 lumen at the most. However these other cyclist with the ultra bright lights are more annoying than safe IMO. At least not safe with any concern for others that can't see after getting flashed close up.
You only need something that will help others pick you out from the background. I don't need a light shined in my face and glares so much that I can't see the path in front of me when on a very shaded section and the bright flash of the oncoming light destroys the adaptation of my eyes to be able to see in the shady areas.
I'm not saying don't use lights during the day. I'm just against some of the lights that put out more than is necessary to be seen. If you only are on a open road in bright sun and no shade then a 1000 lumens might be fine. But on a MUP with dense foliage limiting the sun in some spots, being hit square on by a 1000 lumens isn't fun in close quarters.