Go out and have a friend ride your bike on a nice sunny day and go follow them in a car and see how far back you can be and still see the light blinking. It isn't very far. The brighter the sun the closer you have to be. I ride behind two guys who have the lights on every day when they go out and ride and I have to be close to them to ever be able to see the light. I can the rider himself long before I could ever see his blinker light during the daytime.

You're far better off having bright clothing on as it's a much bigger target than the small blinky light and it won't get 'glared' out by the bright sun.