Separation between two or more lights is more important than the size or shape. On a bike it's seldom practical to install motor vehicle type lights -- too bulky and heavy, and they need too much power.
I few years ago I noticed that cyclists were much more visible, day and night, when they used two headlights and taillights, or mounted the second lights on their helmets. And helmets tend to be visible above the roof lines of most cars, while bike mounted lights can be obscured in traffic. Separation of lights helps with quickly estimating distance, direction and speed, whether a cyclist is approaching or receding.
So I started doing that. I've actually heard drivers and passengers slow down as they were passing and tell me the extra lights made it much easier to see me.
The next best thing we can do for visibility is mount lights that enhance our visibility from the sides. Wheel mounted LEDs are great for that. They really pop against cluttered backgrounds but aren't so bright that they're annoying and don't mess with the vision of fellow cyclists. (Reminds me, I need to put those back on my hybrid errand/commuter bike. I took 'em off a damaged wheel and never got around to remounting them on the new wheels.)