The single flashing LED is a low battery indicator. This is a feature that we added in lights made in mid-2011 or later. As flowlights run at full brightness throughout their battery life, it used to be difficult to tell when the battery was low or didn't have enough juice, as a light will turn on at full brightness and then turn off shortly after, causing people to think that there was something wrong with the light. The low battery indicator resolves this issue.
If you put a fresh battery in and it still flashes - press the button! The flowlight remembers what mode it was last in, so it might have gotten back into low battery mode.
If you have any questions, please feel free to contact us!