I think there is an overkill point. Some of these lights are so bright, you could risk blinding (so to speak) the driver behind you, making it difficult for them to navigate around you. I came home recently shortly after dusk and saw some bikers at the top the hill I was approaching, and I thought a building was on fire and the fire trucks were responding. I'm not an expert by any means, it's just a thought, but I think the brightness of some of these lights could actually cause the car driver to try to look away from them, reducing their visibility and possibly end up in them hitting you or another driver. If you've ever been at a stop light when the sun is low and shining right in your face, it's the same principal. You have to hold one hand up to block the sun so you can see the traffic light. I do think redundancy is good, so I would have two on the front and two on the back. Especially the back because you don't always know if one stops working (which mine does often).