Vehicle headlamps with aerodynamic styling provide for replaceable halogen bulbs. This permits a lens and reflector to remain in place on the vehicle and only requires that a small halogen bulb be replaced should a bulb burn out and require servicing. Replaceable headlamps are optically aimed (at the production facility) with an aimer that registers on three aim "tips" that are molded onto the front surface of each headlamp lens. The aimer device is separate from the headlamps and attaches with a suction cup to the three aim "tips" on the headlamp lens surface. These three tips establish a plane that permits the headlamp to be aimed mechanically, without the headlamp bulb even being lighted.
A production facility aimer has contained within it a level bubble (a curved sealed glass vial filled with mineral spirits and an air bubble) that is used to aim the headlamp vertically. Other production facility aimer features permit horizontal aiming. The aimer is set up so that its internal level bubble is parallel to the axis of the high beam parabola and also parallel to the light emitted from the headlamp. As the headlamp is adjusted with the vertical adjustment assembly, the level bubble in the aimer moves until it is in a position that shows that the lamp is in aim (in the middle of the spirit bubble vial).
Recently, changes in headlamps have affected the three aim tips used for the above-described aimer. Changes in headlamp size have reduced the vertical size of the lens surface to the extent that in some cases there is no room for aim tips or special adapters for the aimers. For these vehicle headlamps, a new aiming device is required. Secondly, the use of "reflector optics" with a clear lens has created a headlamp lens without aim tips. Styling has dictated that the lens be clear so that the tinted reflector surfaces (reflector optics) can be seen. The aforementioned vehicle headlamps also require a new aiming device. Thirdly, headlamps now can have an independently adjustable reflector within an external housing and lens (commonly referred to as an internally adjustable reflector headlamp). Internally adjustable headlamps generally have reflector optics and a clear lens and also require a new type of aiming device.
For the aforementioned new categories of vehicle headlamps, the federal government has required that there be some means of establishing the vertical and horizontal aim of a headlamp after vehicle assembly. Level bubbles are generally used for vertical aiming. Special vehicle headlamp adjusters are used for horizontal aiming.