How come on some cars, one headlight is brighter than the other headlight?

Could be any number of reasons, but I’d suspect the most common was that the lights aren’t aimed properly. One is hitting you right in the eye, the other is off to the side.

Read “Sundials” in the new issue of Aboriginal Science Fiction.

A nice UL I heard back in high school was that if you’re being followed at night by a car with perfectly aligned headlines (each are equally bright) then it’s a police vehicle following you.

I have no idea towards the veracity of this. But, it’s a really good way to keep a 17 year old driving slowly at night.

I think there’s some truth to that actually, only in the reverse direction. If there’s a car behind you and one of the lights is brighter (not aimed properly), you can generally be sure that it’s not a cop–they tend to keep everything on their cars well adjusted. If there’s a car behind you with headlights aimed perfectly, be careful–it could be a cop, but that’s certainly no guarantee that it is.

The headlights are equally bright, they are just focused at different points. Thats why one appears brighter because it is hitting you more directly. The reason they are not focused at the same point it to cover more area in front of you. If they were pointed exactly at the same point, you would have one spot of brightness rather than a field of light in front of you.

I don’t know how often it is done now, but in days past the left headlight was sometimes aimed a little higher than the right. High beams, at least, have to strike a compromise between illuminating the road ahead and dazzling oncoming traffic. Since the right headlight is closer to the line of vision of oncoming cars the compromise point is a little lower than it is for the left headlight.

“Vandelay!! Say Vandelay!!”

Well, there is always the possibility that one bulb is a traditional tungsten filament, and the other is a halogen, that would produce the same pronounced difference in brightness. I would still say that misaimed is just as likely, since both are well within the reach of slobs working on their cars on the weekend, or right after getting a fixit ticket.

I can solve any problem!
Just give me a rifle and a clocktower!

Pluto… I think you are right, but backwards. on all cars, the headlights when adjusted proparly the left headlight is adjusted slightly down so it will not glare into the face of oncomming driver. Unless you drive on the left hand side of the road that is.

B_Line12 – You are correct of course. I got up this morning and looked in the mirror and forgot to look away.

In the past couple of months, I’ve noticed a lot of headlights with a distinctly blue hue to them. What the deal with that?

Funky European imports.

I’ve noticed the headlights with a blue hue, too. Several months ago I saw a thing on the news about these new headlights; they’re brighter and more efficient, kind of expensive. Sorry, that’s all I remember.

Those are metal-halide bulbs. About 60% brighter than Xenon, which is 40% brighter than the yellow halogens. Xenons are white (or bright white) and metal-halides are blue-ish, but only from the front. From the sides, they’re white looking. Very nice. The metal-halides are about $50 a bulb, Xenons are about $15 a bulb. That is, this is all IIRC.


We are the children of the Eighties. We are not the first “lost generation” nor today’s lost generation; in fact, we think we know just where we stand - or are discovering it as we speak.

In Europe the left headlight is usually aimed slightly to the right (and down as someone else said) so that it doesn’t blind oncoming traffic. Of course in Europe you get a lot more windy, two-lane, undivided roads. Don’t know if this is the standard in the US also.

plenty windy narrow roads here, also lots of narrow real straight ones. Don’t know how it is in europe but in the US with our god given gas guzzling ways we rarely carpool,so most cars have only the driver in them. Therefor all the passenger weight is on one side. That naturally makes the other side LIGHTER.
In days past pluto was English. Any body mention dirt or an older bulb?

“Pardon me while I have a strange interlude.”-Marx

I followed that right up to the “In days past…” part.

Rysdad – I think he was referring to my confusing right and left in my earlier post.

What can I say? I’m chirally impaired.

“Vandelay!! Say Vandelay!!”

Halogen headlights must be replaced in pairs.


When one “goes out,” take a guess as to how many replacement headlights are purchased.


Terence in Marietta, GA

Be someone’s hero

Ummmm? Why?

in the long run it is less expensive to replace head lights in pairs, .Replaceing one headlight makes one side of the car lighter than the other. Naturally the tires on the heavier side will wear faster,we all know you should replace both tires on an axle at the same time or the difference in tread will cause you to go in circles. That’s no way to do a longrun. And two tires cost more than two headlights.

“Pardon me while I have a strange interlude.”-Marx