Why are headlamps made of plastic instead of glass?

[ameli0rate]

Wouldn't glass headlamps solve the fading plastic problem? Is it about cost? Weight savings? Impact resistance?

Will a degraded reflector make a glass headlamp useless whether or not the glass is still clear or sandblasted from a few hundred thousand miles?

 

[thermal guy]

They used to be made of glass. Probably plastic is lighter, cheaper,and can take more impacts.

 

[Lynx_Arc]

The main reason glass headlamps aren't used is manufacturing costs. In the days of standardized glass headlamps they could crank out a lot of the same design headlamp on an assembly line driving down the costs of design and setup. Today's cars have different plastic headlamp assemblies to match the look of the car so there is probably over 1000 different headlamp assemblies out there which greatly increases setup changes in manufacturing driving up the cost per unit as it cannot be spread out over hundreds of thousands.... 10s of millions even. I don't see this changing as car makers don't want people to have a vehicle that lasts 25 years or more they don't mind them needing parts after a dozen years leading to people giving up on fixing them and upgrading. Personally I hate plastic headlamps I have one yellow headlamp on my car the other got broken and I replaced it a few years ago. I probably need to consider replacing the other one as my car is getting very old and parts are harder to find now.
If anything they need to find a plastic that is UV immune or a way to easily and cheaply recoat them on a regular basic to avoid damage.

 

[Alaric Darconville]

Why does any company do anything? To make money. Why do they make things one way instead of another? To save money.

Saving money is making money-- if your lamp assembly costs $X less to make because it uses plastic instead of glass, you've saved $X x [sales of that year's model].

The manufacturer only needs to sell that car once, so they're not too interested in making the headlamps last much longer than the law itself requires.

 

[aznsx]

The main reason glass headlamps aren't used is manufacturing costs. In the days of standardized glass headlamps they could crank out a lot of the same design headlamp on an assembly line driving down the costs of design and setup. Today's cars have different plastic headlamp assemblies to match the look of the car...

Cost always plays a role, but you hit the big reason: These days of uni-blob look-alike cars, often mono-chrome and devoid of 'shiny stuff' as well, headlamps (and tail lamps) are 'bout the only things left for the stylists to go crazy with to try to differentiate their otherwise rather boring designs. The front grille is often the primary 'signature' piece, and the headlamp units are 'blended' in with that.

IMO, everything I see around me is either a 'box', or a uni-blob sedan - both of which leave me cold. It's a bit of a shame I think, but that's only because I'm old enough to remember better (IMO) days in automotive styling.

 

[Lynx_Arc]

Cost always plays a role, but you hit the big reason: These days of uni-blob look-alike cars, often mono-chrome and devoid of 'shiny stuff' as well, headlamps (and tail lamps) are 'bout the only things left for the stylists to go crazy with to try to differentiate their otherwise rather boring designs. The front grille is often the primary 'signature' piece, and the headlamp units are 'blended' in with that.

IMO, everything I see around me is either a 'box', or a uni-blob sedan - both of which leave me cold. It's a bit of a shame I think, but that's only because I'm old enough to remember better (IMO) days in automotive styling.

Part of all of the uni-blob is gas mileage I believe that the shape is the most energy (less wind resistance) efficient and like you said the headlights are designed to look cool, not be easy to make and replace.

I'm hoping that in the future that manufacturers go to LED lights with a few optimized designs for the LED focusing/reflecting assembly that mounts behind a plastic shield covering it that is cheaper to make and replace and the light assembly can be upgraded or swapped out for other designs as the technology improves. It would be easy to make a clear piece of plastic that is molded curves to cover your LED module than an all-in-one light and cover assembly that is one piece construction.

 

[rlhamil]

New cars sold in the US from about 1940 to 1983 were required to have sealed beam headlights - at first, two 7-inch round ones being the only option; later, four (separate high and low beam) smaller round ones, and later still, two large or four smaller rectangular ones.

Those were necessarily glass, contained an internal reflector, and the front glass was heavy enough to be impact resistant. They were mostly easy if tedious to change (front plate plus retaining bracket, each with screws). They had the advantage of each one including all the parts, and being like a lightbulb in that all the internal parts are totally weatherproof - and since they were all otherwise fairly traditional incandescent bulbs (even if halogen), they burned out, and the whole sealed beam was replaced.

By 1983, under pressure from auto makers pointing to cars in the European market's reasonably successful use of non-sealed-beam headlights with few of the problems seen in pre-1940 headlights (including corroded reflectors, etc), those were allowed in the US too.

For probably all three of the reasons in the original question (cost, impact resistance, weight) with varying priority, the front clear part was usually plastic. That may have gotten better over the years, but I'd guess that unless they've gotten a lot better, they show their age after a decade or so, depending on climate and usage.

Buses, emergency vehicles, commercial heavy vehicles, pickup trucks (to some degree), etc, still favor sealed beam headlights (even if they're not incandescent and not one continuous piece of glass except where the wires come out), probably for reliability and ease of maintenance, and because style is less of a concern on such vehicles.

 

[-Virgil-]

Wouldn't glass headlamps solve the fading plastic problem?

Yes. It was the other way around; plastic lenses created this problem.

Is it about cost? Weight savings? Impact resistance?

Impact resistance and lower weight were things Ford, on behalf of GE Plastics, harped on as "consumer benefits" when they convinced NHTSA to create this crappy mess we now live with. Lower cost and shorter headlamp life (more parts sales and then faster obsolescence) were automaker benefits Ford didn't talk about out loud. People die unnecessarily because of this regulatory capture (a term that means when a regulated corporation or industry manages to pervert the regulatory process or agency to get their own interests prioritized). Stern did a writeup about it here.

There are styling designs that are possible to do in plastic but not glass. There are also plastic materials and coatings that hold up a whole lot better than what we have, but -- surprise! -- automakers won't pay for lenses that are any better than they legally have to be, and legally they don't have to be very good.

Will a degraded reflector make a glass headlamp useless whether or not the glass is still clear or sandblasted from a few hundred thousand miles?

Yes. Degraded reflector = useless headlamp, no matter what the lens is made out of. And by the time you can actually see the degradation of the reflector, it was dead months or years before.

 

[-Virgil-]

(Sealed beams) were necessarily glass

Until the late 1970s, when GE (with their in-house plastic and chemicals division) began playing around with plastic sealed beams. This was actually a good idea. A sealed beam is intended as a finite-life, throw-away item, so it likely would burn out before much lens deterioration. And the problems of accurately molding a glass reflector are not present with a plastic one.

They were mostly easy if tedious to change (front plate plus retaining bracket, each with screws). They had the advantage of each one including all the parts, and being like a lightbulb in that all the internal parts are totally weatherproof - and since they were all otherwise fairly traditional incandescent bulbs (even if halogen), they burned out, and the whole sealed beam was replaced.

Other big advantages of uniform-size sealed beams: any improvements were automatically applied to older cars as their headlights got replaced...all vehicles had pretty much the same headlight performance, which made it much easier to optimize the placement and reflectivity of road signs and meant everyone had pretty much the same seeing and faced pretty much the same glare...they were all aimed using the same technique (no need to search for deliberately-invisible lens markings and refer to books about the various aim methods and just give up)...all headlights looked alike, so any funny business with lights that didn't belong (wrong color, wrong kind, etc) was quickly and easily pinched by any half-awake traffic cop...etc.

By 1983, under pressure from auto makers pointing to cars in the European market's reasonably successful use of non-sealed-beam headlights with few of the problems seen in pre-1940 headlights (including corroded reflectors, etc), those were allowed in the US too.

That wasn't their line of argument, because it wasn't true. Ford's argument, aside from those listed above, were about aerodynamics. and (massively over-stated) fuel economy improvement potential. The Europeans actually had more than plenty of reflector corrosion, in large part because their regulations didn't (still don't) have any durability or environmental-resistance requirements. That's why Ford put in their petition for a system that was supposedly "sealed" except during bulb removal/replacement. O-ring on the bulb (not present on any of the European bulbs), no vent or drain provisions in the lamp, lens solidly glued to the reflector.

Buses, emergency vehicles, commercial heavy vehicles, pickup trucks (to some degree), etc, still favor sealed beam headlights

This statement is about 15-20 years behind the times.