Originally Posted by a1penguin

800 lumens on the helmet seems fairly bright, if you are riding on the streets rather than off road. Shining 800 lumens into the eyes of a driver might adversely affect their vision enough to cause them to run into you :-)

I think 400 lumens on the helmet is more than enough. The idea of the helmet light is that you can point it in direction other than where the bike is going. An 800 lumen light is also going to be heavier and some people complain that helmet lights are "too heavy". I have a small 400 lumen cylindrical flashlight (0.9" diameter, 4.5" length), 18650 battery on my helmet and it's more than adequate.