Iirc..... Looong pause.
. ...... Think it was an Army experiment in camoflage. They placed a tank on a horizon or ridge and covered it in bright lights. The tank disapeared almost entirely in broad daylight. The light level emited matched that of the sky behind to a degree that wasnttoo acurate and the effect was enough for the tank to be invisible unless you knew where it was before lights on.
So, point is, the more of the vehichle covered in light the harder it is to see and judge distance and speed. There is a balance to be had, i'm sure you've all seen bikes with lights on low beam in day time, and some of those are dumb enough to use high beam in day time. With an urban background the bike will stand out where as the tank on a horizon will not, however it is almost impossible to judge the bike speed and distance as all you see is light, theres nothing to focus on.
So as Kev says, excessive light doesnt help. Therefor too bright a light.... You get the gist, to pinch an H'ism.