Originally Posted by
canklecat
I've found it more helpful to elevate the rear lights than make 'em brighter. Add red lights to the rear of the helmet, clipped onto a backpack, back of the jacket/jersey, or on a trunk bag. Gives vehicles a better chance of seeing the lights in traffic. During nighttime group rides I've noticed bikes with rear red lights only on the bikes themselves -- on the rear rack or lower -- can't be clearly seen in traffic because some cars physically block the view. But if the cars can see the rider's helmet or torso, they can see a red light mounted higher.
It may depend. When I see a cyclist having lights on their helmet, it looks like a light from some poles in distance, unconnceted to the rider. On the other hand, when I have rear lights mounted on the lower part of the seatstays or the legs of the rear rack, they lighten the ground and produce a large (flashing) red area on the road that follows the bike; I suppose that helps with visibility (provided there is a taillight in higher position, too).