Not too sure what you mean by open lens. Most people purchase projectors for 2 reasons. They like the look with the Halo Rings or they plan on eventually getting a true HID system.
The later is the reason there is such a controversy with HID from the gov't. HID aftermarket in a car not designed for it will provide tons of glare to the on coming traffic. This is only if the car manufacture never developed the headlights for HID. So when you put in the Projector Headlights you focus your beam more so to the road and not distract the on coming traffic. This is not a cure all, since there will still be glare, it just reduces it a lot and lessens the likelihood of any problems.
Additionally HID is color customizable. Depending upon the K rating gets you certain type of color in the headlights.
Does this answer your question?