Glass versus plastic headlight lenses

Mr. Merk

Newly Enlightened
Joined
Dec 22, 2018
Messages
159
Location
NW Arkansas
My Cibies never did, even after 20 years? My Hellas never did? And I went up close to the Corvettes and they had no protective covering, I am sorry to say, being a lifelong Chevy fan!

Most modern headlights are vented and not sealed (as Virgil pointed out,) so some condensation is normal and will evaporate. What you were told is true regarding standing water is the standard across all brands (at least the ones I've worked for.)
 

scootertrs

Newly Enlightened
Joined
Jan 7, 2022
Messages
15
Location
Florida
By the way, I just remembered, my Indian motocycle (motocycle is correct Indian speak... only recently did they switch to motorcycle) had a glass headlamp with a replaceable bulb. I never had, nor have a problem with her in that respect. True she was built in 1947, but still sports the same headlight (not too bright-have to light a match to see if its on -:)) but may also be due to the 6V system.
 

alpg88

Flashlight Enthusiast
Joined
Apr 19, 2005
Messages
5,395
Excessive fogging can be fixed, unless your headlight is damaged, and needs to be replaced, the fix is cheap, there are only 2 other reasons;
1 clogged vent, thus no airflow,
2 damaged seal.

to unclog the vent often the light does not even need to be removed, if the seal/adhesive between the housing and the lens is cracked we reseal it, the light needs to be removed. last few years we use uv cure glue, dries in seconds and rock hard.
The ideal solution would be replacing it, but no one will pay 300-500 to replace lights that work and not shattered.
 
Last edited:

eggsalad

Enlightened
Joined
Mar 30, 2013
Messages
268
why glass lenses are better in the terms that matter (crashes/deaths).

"Matter" to whom? Those terms might matter to the general public, and to the government in terms of safety, but the only thing that matters to the manufacturers who make plastic headlights instead of glass is profit.
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
11,212
Location
Tulsa,OK
It would be nice to see a standardized smaller sealed beam headlight assembly that fits behind a clear plastic lense that can be very cheaply replaced every few years but I don't think that would be profitable. I would also like to see wiper blades that last 5-7 years or longer instead of 1 year.
 

John_Galt

Flashlight Enthusiast
Joined
Feb 20, 2009
Messages
1,836
Location
SW, PA
A lens in front of the lamp could/would cause additional glare, or alter the beam pattern. This is one of the reasons that diy-ing a projector retrofit is so thoroughly frowmed upon. A return to a sealed beam type system would have the potential to be good, but would also present an opportunity for either SAE or the government to kneecap the change in some glaringly stupid and shortsighted way, as is tradition.

As it stands, there at least nominally exists the ability to upgrade or supplement the performance of your vehicles existing lamps (excluding LED systems).
 

Mosports

Newly Enlightened
Joined
Aug 3, 2016
Messages
7
I may be wrong, but I believe the change to Polycarbonate lenses is due to larger and less vertical many of todays headlamps are. Glass lenses are heavy and at some point, large horizontal lenses can not support their own weight without getting too thick and expensive.
 

alpg88

Flashlight Enthusiast
Joined
Apr 19, 2005
Messages
5,395
Weight is probably a factor , but it most likely has to do with more complex shape of new headlights,
 

och

Newly Enlightened
Joined
Sep 15, 2011
Messages
129
I dont think there are many cars left with glass headlights, but quite a few still use glass fog lights, or were using them until very recent.
 

TechGuru

Newly Enlightened
Joined
Sep 24, 2017
Messages
139
Location
TEXAS
I dont think there are many cars left with glass headlights, but quite a few still use glass fog lights, or were using them until very recent.
anything that still uses sealed beam since sealed beams are glass...
 

theory816

Newly Enlightened
Joined
Oct 5, 2016
Messages
103
Both arn't bad choices. Glass is more scratch resistant than polycarbonate and PC won't shatter if it gets hit by a rock.

The key thing that manufacturers shouldve done was make the front cover removeable and replaceable. Having it sealed and glued shut makes glare and visibility a problem down the road.
 

idleprocess

Flashaholic
Joined
Feb 29, 2004
Messages
7,197
Location
decamped
The key thing that manufacturers shouldve done was make the front cover removeable and replaceable.
While this would be good for consumers, it's bad for the automakers' bottom line - parts are a significant source of highly profitable revenue with gross margins often in excess of 100%. Warranty work performed by dealers almost certainly mandates the use of OEM parts and insurers might insist as well for body work, thus there's some demand inelasticity. By the time the market for a given headlight assembly becomes price-sensitive the aftermarket can chase those low margins.

...

When I worked for a small manufacturer we marked up commodity stuff by 400% over COGS - even more for our own proprietary components. Net margins on that line of business were significantly lower since processing orders requires most of an employee's time, required carrying inventory for long periods of time, and also necessitated ordering irregular inventory for the spares business (being able to reliably ship spares within ~1 business day was critical to the overall business).

Why the independent service firms bought commodity parts from us was always somewhat mysterious - they could read the labels and order from the likes of Mouser, Grainger, et al easily enough. Some may have had service arrangements with their customers requiring the use of OEM parts; others may have had agreements billing replacement parts on a "cost plus" arrangement. Either way thus paying 4x as much for a microswitch meant 4x the margin so long as they had a magic OEM invoice.
 

turbodog

Flashaholic
Joined
Jun 23, 2003
Messages
6,425
Location
central time
I may be wrong, but I believe the change to Polycarbonate lenses is due to larger and less vertical many of todays headlamps are. Glass lenses are heavy and at some point, large horizontal lenses can not support their own weight without getting too thick and expensive.

The windshield would like to have a word with you...
 

theory816

Newly Enlightened
Joined
Oct 5, 2016
Messages
103
While this would be good for consumers, it's bad for the automakers' bottom line - parts are a significant source of highly profitable revenue with gross margins often in excess of 100%. Warranty work performed by dealers almost certainly mandates the use of OEM parts and insurers might insist as well for body work, thus there's some demand inelasticity. By the time the market for a given headlight assembly becomes price-sensitive the aftermarket can chase those low margins.

...

When I worked for a small manufacturer we marked up commodity stuff by 400% over COGS - even more for our own proprietary components. Net margins on that line of business were significantly lower since processing orders requires most of an employee's time, required carrying inventory for long periods of time, and also necessitated ordering irregular inventory for the spares business (being able to reliably ship spares within ~1 business day was critical to the overall business).

Why the independent service firms bought commodity parts from us was always somewhat mysterious - they could read the labels and order from the likes of Mouser, Grainger, et al easily enough. Some may have had service arrangements with their customers requiring the use of OEM parts; others may have had agreements billing replacement parts on a "cost plus" arrangement. Either way thus paying 4x as much for a microswitch meant 4x the margin so long as they had a magic OEM invoice.

Alot of it may also be due to sealing out moisture and water. If the cover is replaceable and detachable, there may be a way for water to make its way in in a rainy situation. But I'm not sure what you meant in your post.
 

idleprocess

Flashaholic
Joined
Feb 29, 2004
Messages
7,197
Location
decamped
Alot of it may also be due to sealing out moisture and water. If the cover is replaceable and detachable, there may be a way for water to make its way in in a rainy situation.
It's simpler/cheaper/more robust to use adhesive to fuse the lens to the housing to largely eliminate rain/splash ingress. OEM headlights aren't airtight since moisture in the air itself can condense on the interior thus a splash-resistant vent or few exists on the backside.

But I'm not sure what you meant in your post.
I was otherwise expanding on the business case against selling anything other than complete headlamp assemblies at terrific markup. The market might wish for it but the OEMs' accountants and shareholders won't.
 

alpg88

Flashlight Enthusiast
Joined
Apr 19, 2005
Messages
5,395
. Warranty work performed by dealers almost certainly mandates the use of OEM parts and insurers might insist as well for body work, thus there's some demand inelasticity.
Yes and no, for cars over certain milage (iirc 12k) insurance does not pay for new oem parts, only used or aftermarket, so if you crash a car with 20k miles, your insurance will most likely not pay for new headlights. also unless you are fixing your car at actual dealer's body shop, and it is that shop that installed a non new oem part, your warranty will be honored by the same dealership, if you fix your car at non dealer shop, or a shop not certified by your insurance company, you may have issues if your next warranty work will need to be done to parts of the car affected by collision, you can insist all you want, but it wont change what insurance pays for a certain part. and other dealer may very well refuse a warranty work on such car.
 

N8N

Flashlight Enthusiast
Joined
Apr 26, 2013
Messages
1,243
You may find some cars with plastic headlights in the United States shipping with glass headlights in Europe and other parts of the world.

This at least is true. My (Mk4) GTI came with plastic lenses, but the ECE versions of the same headlights use glass.

My knowledge is WAY out of date, but I believe that at least it used to be that in the US, the light had to be an assembly, while the ECE regs allowed replaceable lenses. For some reason VW chose plastic for US and glass for ECE. I want to say that the same thing was true of the older Corrado although I cannot actually remember if the US headlights were plastic, only that they were beyond awful, as if VW engineers were punishing us for not harmonizing our headlight regs with ROW.
 

aznsx

Flashlight Enthusiast
Joined
Apr 24, 2015
Messages
1,729
Location
Phoenix, AZ USA
This at least is true. My (Mk4) GTI came with plastic lenses, but the ECE versions of the same headlights use glass.

My knowledge is WAY out of date, but I believe that at least it used to be that in the US, the light had to be an assembly, while the ECE regs allowed replaceable lenses. For some reason VW chose plastic for US and glass for ECE. I want to say that the same thing was true of the older Corrado although I cannot actually remember if the US headlights were plastic, only that they were beyond awful, as if VW engineers were punishing us for not harmonizing our headlight regs with ROW.
Disclaimer:

For the record, since this old screwed up post (which ironically the system apparently won't allow me to edit) has now been 'quoted', I want to note that this included 'quote' is not anything I ever personally stated as fact, but is rather a quote of info I had quoted from another outside source, the link to which was later inappropriately removed by a (past?) moderator causing it to appear that it was a quote of something I had stated myself, which is of course no fault of yours, N8N. I (as I originally stated) have no info as to the validity of the info referenced at that link that I included, which was later inappropriately removed by editing by said moderator. If this is confusing, that's because it should be. This is what happens when someone inappropriately edits someone else's post.

As you were...
 
Top