What are the three bumps on headlight lenses?
June 2, 2005 5:57 PM   Subscribe

What's the deal with the three rounded-cone-shaped bumps on the exterior surface of plastic headlight covers [lenses?]? (The grid-patterned kind of headlight lenses, not the new superbright ones.)

I noticed this while walking home today; it looks like *most* grid-lenses have bumps, irrespective of the lenses' shapes and whether the cars are domestic or foreign. Newer cars with the really bright [Xenon?] headlights don't have them, and neither do the cars of the Chicago PD. Xenon lamps also tend to have a clear lens with no grid pattern, if that matters. I only saw them in a classical triangle formation (right side up). Here's a picture with them circled on a grid-patterned lens (24k) What are they for?
posted by michaelkuznet to Travel & Transportation (10 answers total) 1 user marked this as a favorite
 
I imagine they come from fabrication. As in, the points where they are secured to the machinery that moves them through the fabrication process. (I have no idea how they're manufactured, mind you).
posted by Hankins at 6:03 PM on June 2, 2005


They are used by the machine that aims headlights as reference points.
posted by Mitheral at 6:05 PM on June 2, 2005


Mitheral is right.
posted by Kirth Gerson at 6:17 PM on June 2, 2005


Hmm. I figured that because not all lenses had them, that that couldn't be the case. How do Xenon headlamps get aimed? How about normal ones that don't have the bumps? Is there any description of the headlight-aimer machine online?
posted by michaelkuznet at 6:42 PM on June 2, 2005


I always thought they were where the injection-molding machine would have injected the glass...
posted by five fresh fish at 6:57 PM on June 2, 2005


I could easily be wrong but I didn't think today's headlights were adjustable. With mine I just replace the inner bulb. My initial reaction was that they were there because of the molding process but the idea about them being there for aiming sort of makes sense.
posted by Carbolic at 8:18 PM on June 2, 2005


I'll add, I remember headlight aiming machines back in the 70's but I haven't come into contact with one in years.
posted by Carbolic at 8:29 PM on June 2, 2005


Point of reference, my '98 chevy truck still has aimers...yes, you only replace the bulb and not the lens, but the whole lens gets aimed.
posted by notsnot at 9:55 PM on June 2, 2005


The headlights you see without bumps have little level vials built into them. Many HID style lights have automatic aimers that keep the low beam cut off pointing down even when the rear is heavily loaded.

I've never actually seen the aiming devices. My understanding is the aimer is just a level vial like above mated to a set of three arms. the arms are graduated. You look the values for each are up in a reference and then set the arms to the values. You then set the three arms on the three little bumps and use the vial to set the headlight.
posted by Mitheral at 8:49 AM on June 3, 2005


Carbolic writes "I could easily be wrong but I didn't think today's headlights were adjustable."

Most headlights are still adjustable (I'd say all but I'm not an ASE or anything, undoubtably there is a 2006 Hupmobile out there with fixed headlights or something) in order to allow adjustments to be made after collision repairs and to allow for assembly tolerances.
posted by Mitheral at 9:58 AM on June 3, 2005


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