My light comes on when I wheel my bike into the garage. Totally unscientific testing just conducted in my garage, says the light is just as bright at 4 miles an hour as it is at 8. Ours stay on for five minutes after you stop moving. They do noticably dim then and I don't think they are bright enough to change a flat. So I carry a small extra light if I know I'll be riding after dark.

We have the Lumotec IQ Fly N-Plus W/Standlight.

Veronica