I noticed that on bikes I've seen on the road, their pretty bright when looking at them head on but as you begin to pass the light almost goes from bright to dim to nothing! I've noticed this on some other lights too including my homemade Cygolite ExpiliOn 350 I converted to a tail light. But I use other rear lights that are visible from the sides, but I may consider getting another light to replace the Cygolite due to that flaw.