Car makers intentionally creating a safety hazard?

[AZhitman]

Easy answer.

I'll give my pathetically weak layman's interpretation, but we should REALLY hit up simmsled, who has been an automotive lighting designer / engineer for damn near a decade.

I won't get into the misinformation about polycarbonate (not "acrylic") housings, lumens / distance requirements, or any of those things.

The Feds mandate the minimum overall front-facing surface area (and rear-facing) of headlights and taillights. The Feds ALSO mandate CAFE standards, which indirectly dictate things like weight and coefficient of drag (in pursuit of compliance with EPA mileage ratings). The Feds ALSO madate pedestrian safety measures.

So, you've got all the engineers working together. The headlight guy wants to use a glass, sealed-beam headlight. However, the physical properties of glass lenses for lights dictate that it needs to be a flat, upright surface (such as an S13 popup headlight). Too heavy. Too drag-inducing. Too dangerous for pedestrians. Not enough illuminating surface area. Not slippery enough. Did we mention it's too heavy? And the coup de grace comes when the "designer" comes in and says, "It's ugly."

Polycarbonate is a fine material for headlight housings if it's maintained.

Lobbyists have successfully killed vehicle inspections in many states, so it;s totally legal to drive around with one dim yellow headlight. I support vehicle inspections, but it's become political - I won't get into WHO opposes vehicle inspections, but suffice it to say, their argument is that it "unfairly penalizes lower income individuals".

Smell what I'm cookin'?

So, Brien, you're not "wrong" per se. But the entities to blame are not who you think they are. You really should get involved in SEMA's Political Action Committee if you care. We do some interesting stuff.

[AppleBonker]

Tempering the glass puts the surfaces under a compressive force and the inner material is under tension. It is this stress gradient that causes the glass to crack and shatter so violently. Chemically speaking, the material is the same.

[AZhitman]

Tempered glass with a special coating on it to keep the cubes from spreading out in a crash. We've come full circle now. Are you happy?

Nope.

Windshields are generally laminated, not tempered. Side glass is typically tempered, not laminated.

Hope that helps.

[Dattebayo]

I won't get into the misinformation about polycarbonate (not "acrylic") housings, lumens / distance requirements, or any of those things.

lol I admit I should have seen that. One has coating, the other does not. DOH!

[Dattebayo]

Windshields are generally laminated, not tempered. Side glass is typically tempered, not laminated.

Hope that helps.

Seriously, that was the information I had. Got a link?

[AZhitman]

Yep. It's www.insidegregshead.com.

Accident investigation manual. Memorized bits and pieces of it.

You weren't wrong. Side glass is usually tempered, altho some luxury automakers are now laminating their tempered glass. If a windshield was tempered, a rock chip would, through breaking the surface tension, shatter it into cubes (like a sliding glass patio door when your weedeater whips a pebble at it... GRRRR).

The lamination keeps the shards together - Look at pics of a windshield hit by a baseball or a head - It deforms, cracks in the area of the impact, but some parts of the glass can remain clear and unbroken.

[AppleBonker]

Greg wins (and I almost tried to click that link). Guess I wasn't as knowledgeable on the application of tempered glass as I was on the tempering process itself. The rear window is also commonly tempered. Windshield makes sense though.

Except that surface is in compression, not tension...

[AZhitman]

^ Yep. That.

[PoorManQ45]

Thanks for chiming in Greg.

I miss simmsled. He used to be a mod in the electronics section. We'd go back and forth on designs when helping people out years ago

[Jesda]

DOESNT MATTER ANYWAY

FUTURE CARS WILL LOOK LIKE THIS:



Just kidding. We're going to be forced to ride the bus for the "good of mankind." I just hope there's a separate business section far away from the crazies.

[s0m3th1ngAZ]

Easy answer.

I'll give my pathetically weak layman's interpretation, but we should REALLY hit up simmsled, who has been an automotive lighting designer / engineer for damn near a decade.

I won't get into the misinformation about polycarbonate (not "acrylic") housings, lumens / distance requirements, or any of those things.

The Feds mandate the minimum overall front-facing surface area (and rear-facing) of headlights and taillights. The Feds ALSO mandate CAFE standards, which indirectly dictate things like weight and coefficient of drag (in pursuit of compliance with EPA mileage ratings). The Feds ALSO madate pedestrian safety measures.

So, you've got all the engineers working together. The headlight guy wants to use a glass, sealed-beam headlight. However, the physical properties of glass lenses for lights dictate that it needs to be a flat, upright surface (such as an S13 popup headlight). Too heavy. Too drag-inducing. Too dangerous for pedestrians. Not enough illuminating surface area. Not slippery enough. Did we mention it's too heavy? And the coup de grace comes when the "designer" comes in and says, "It's ugly."

Polycarbonate is a fine material for headlight housings if it's maintained.

Lobbyists have successfully killed vehicle inspections in many states, so it;s totally legal to drive around with one dim yellow headlight. I support vehicle inspections, but it's become political - I won't get into WHO opposes vehicle inspections, but suffice it to say, their argument is that it "unfairly penalizes lower income individuals".

Smell what I'm cookin'?

So, Brien, you're not "wrong" per se. But the entities to blame are not who you think they are. You really should get involved in SEMA's Political Action Committee if you care. We do some interesting stuff.

Why can't they make glass lenses? Doesn't necessarily have to be a square, sealed beam affair. You can manufacture glass in any shape you want. The only issue, then, would be weight...and that minimal.

[AZhitman]

<sigh>

On this one, you're gonna have to put on your engineer hat.

Think about it.



Sure, you can replicate that shape in glass. Now, make it thick enough to withstand a pebble striking it at 80mph. And, since it's almost horizontal, it's gonna need to withstand light hail. Now, you need to make sure it'll withstand rapid heating / cooling (such as sitting in 120-degree heat, reaching 180-degrees, and then being hit with 50-degree water from a hose or a car wash).

How thick is the glass on a sealed beam headlight? How do you think that would look (for the design above)? We're talking about a substantial weight increase. You can't make it like a damn wine glass.

[AppleBonker]

That one would look better bedazzled...

[Jesda]

<sigh>

On this one, you're gonna have to put on your engineer hat.

Think about it.



Sure, you can replicate that shape in glass. Now, make it thick enough to withstand a pebble striking it at 80mph. And, since it's almost horizontal, it's gonna need to withstand light hail. Now, you need to make sure it'll withstand rapid heating / cooling (such as sitting in 120-degree heat, reaching 180-degrees, and then being hit with 50-degree water from a hose or a car wash).

How thick is the glass on a sealed beam headlight? How do you think that would look (for the design above)? We're talking about a substantial weight increase. You can't make it like a damn wine glass.

That looks gay anyway. Enough with the cat eyes.

[C-Kwik]

I was going to post earlier but ran out of time before class started. Greg pretty much covered one part of what I was going to say. Actually much more comprehensively.

The problems are two fold
1: Ultra Clear glass is capable of 98~99% light transmission. Acrylic maxes around 92%.

Care to share your sources about the light transmission? PC (polycarbonate) is not that different than glass optically. There does appear to be some difference here and there, but what matters most here is in the visible spectrum. So depending on how it was measured and in what form (different applications of glass and plastics may use coatings for specific purposes) each were measured in, its hard to make a direct comparison. That said, PPG's Ultra-clear Glass (I'm assuming that's the product you were referring to) states on their site that the light transmission is 92% in the visible light range. Soda lime glass appears to have about 92% throughout most of the visible range dropping off some as it approaches redder colors:

http://www.sinclairmfg.com/datasheets/sodalimecurve.htm

Not sure what pure polycarbonate light transmission is (I couldn't find a graph for non-treated PC) but many sites claim to be about 92%. From a practical standpoint, there is little difference optically.

I will agree the yellowing affect is disconcerting. My Titan is starting to show signs of the protective coating wearing out. What I am curious about though and have been thinking about for some time now is if Clear Bras might help. I had it on the headlights of the G35 when I had that but never got a chance to see how well it might prevent the oxidization of PC. It would ultimately protect the UV protective layer and add its own level of protection (Clear Bras block UV from my understanding). I noticed no discernible loss of lighting performance with the clear bra on (admittedly, my eyes are not light meters so take it for what its worth).

[Jesda]

[PoorManQ45]

Care to share your sources about the light transmission? PC (polycarbonate) is not that different than glass optically. There does appear to be some difference here and there, but what matters most here is in the visible spectrum. So depending on how it was measured and in what form (different applications of glass and plastics may use coatings for specific purposes) each were measured in, its hard to make a direct comparison. That said, PPG's Ultra-clear Glass (I'm assuming that's the product you were referring to) states on their site that the light transmission is 92% in the visible light range. Soda lime glass appears to have about 92% throughout most of the visible range dropping off some as it approaches redder colors:

I use specialty glass when building flashlights. http://www.flashlightlens.com/str/index ... f=ucl_lens

Nikon Scopes offer >92% light transmission with their multicoat system. I just purchased a Vortex Viper that boasts >%95 percent transmission.

*note* I did not quote the numbers from the exact product used in vehicles. They were max numbers.

[AZ89two4Tsx]

TL:DR. I bet someone already posted what I'm about to say.

Glass is a superior material for headlights, but it cannot be formed into the shape that most new cars demand for them to be.

Example, Volvo XC90 or whatever it is.



Plus, glass is heavier and I'm sure some pedestrian died in a freak glass headlight accident at one time.

[Jesda]

Good. I hate pedestrians.

[Razi]

Me too.
My pop-up headlights shall stab them if they cross my path!

[Red coupe]

Many interior plastics release gasses that, over time, can build up as a film and cloud windows...
This creates a hazard, all car manufacturers should equip their entry level economy cars with solid oak dash boards. To do anything less is negligence.

[AZhitman]

Many drivers release gasses that, over time, can build up as a film and cloud windows...
This creates a hazard.

FTFY.

[Jesda]

Many interior plastics release gasses that, over time, can build up as a film and cloud windows...
This creates a hazard, all car manufacturers should equip their entry level economy cars with solid oak dash boards. To do anything less is negligence.

Make it endangered redwoods and so in.

[PoorManQ45]

Hey Greg, I was just thinking about something.

You mentioned a big reason for dropping glass is the inability to form it to complex shapes reasonably.

I was looking at a 95 Ford e150 van today with foggy lights. What would be the reason for using plastic lenses on vehicles where aerodynamics is not of much concern? Full size vans and trucks mostly.

[Razi]

Production costs?
I dunno, ask Ford.

[AZhitman]

I was looking at a 95 Ford e150 van today with foggy lights. What would be the reason for using plastic lenses on vehicles where aerodynamics is not of much concern? Full size vans and trucks mostly.

Probably safety standards, still (and durability). Glass doesn't deal well with rock strikes. I'm sure insurance companies had some say in the matter.

BTW, great historical info: http://en.wikipedia.org/wiki/Headlamp

[Jesda]

We have a continent littered with cars that can't see. The only safety gained is... none.

[IBCoupe]

Cars don't have eyes, silly.

EDIT:
I stand corrected - some can see out their butts.