Originally Posted by
znomit
Cateye use a light sensor and accelerometer on there "auto" lights, not especially expensive, lights are always on when its dark and you're moving. Its sensitive enough that it won't turn off when you're stopped relatively motionless at a stop light.
These aren't daytime bright though.
TL-LD570-R | CATEYE
This is nearly perfect. You could tape over the light sensor so it always thinks it is dark, so it would rely only on the motion sensor. The trouble is that it's a tail light, and OP (@bmeehan1966) is asking for a headlight. I'd love to know if this exists.