Brown headlamp glass

[JohnR66]

While driving today, I saw a Chevy van with the plastic headlamp lens that
had severe UV radiation damage. It was turning a brown color. No way could
usable light get through it. I've seen them a bit hazy and even yellowed but
never this bad. The drivers side lamp was not as bad, still a tan color, but
night driving must be a no-no with that van.

Polycarbonate does not withstand the sun too well. Why not use impact
modified acrylics? Skylight manufacturers often use it and it stays clear
for many years after the punishing direct UV and weather.

John

 

[Douglas G. Cummins]

Impact resistant acrylics should work just as well as UV-resistant
polycarbonates - provided you do them correctly (which, sadly, most lamp
manufacturers tend not to do because they're more interested in saving
money). The main reason impact resistant acrylics are not used (at
least, not in the U.S.) is because they have not been approved by
DOT/NHTSA. The reason they have not been approved by DOT/NHTSA is that
no one has submitted supporting data which demonstrates better
performance.

Now, following the same trend of polycarbonate lenses, should impact
resistant acrylics be accepted for use on headlamps you'll start to see
a trend of more and more shattered headlamp lenses on cars because the
lamp manufacturer didn't use the correct plastic formulation, and
regular acrylic can not withstand a typical impact from road debris.

 

[Daniel J. Stern]

While driving today, I saw a Chevy van with the plastic headlamp lens
that had severe UV radiation damage. It was turning a brown color. No
way could usable light get through it. I've seen them a bit hazy and
even yellowed but never this bad. The drivers side lamp was not as bad,
still a tan color, but night driving must be a no-no with that van.
Polycarbonate does not withstand the sun too well.

It does if it's properly formulated and coated. Unfortunately, as Mr.
Cummins has noted, a great many North American-market lamps are not
constructed with adequate UV resistance.

Polycarbonate headlamp lenses manufactured to comply with European ECE
specifications don't cloud up and turn yellow as quickly or severely as
US-compliant lenses do at comparable lattitudes. The European lens
material test is both stricter and quicker, so lens materials are better
and more up to date. The US test is lax and takes between 3 and 6 years,
so lens materials are inferior and out of date. The differences are
between the US Arizona/Florida tests, which take at least 3 years and
*don't* require an actual sample of the lens or bonded unit to be tested
(only just sample plates of the material to be tested -- these are always
specially prepped by the makers to ensure a test pass!), and the ECE
high-dose UV test, which takes hours rather than years, and *does* require
actual samples of each and every finished lens or bonded unit.

Why not use impact modified acrylics?

Impact resistance is a problem even with impact-modified acrylics.

Best: replaceable hardened-glass lenses
Next-best: replaceable unhardened-glass lenses
Next-best: replaceable polycarbonate lenses


DS

 

[Daniel J. Stern]

While driving today, I saw a Chevy van with the plastic headlamp lens
that had severe UV radiation damage. It was turning a brown color. No
way could usable light get through it. I've seen them a bit hazy and
even yellowed but never this bad.

Probably an older aftermarket (non-GM) headlamp. GM's polycarbonate tends
to be moderately "less bad" than found on other domestic makes. I can
think of one vehicle model that consistently develops very dark brown
discolouration to plastic headlamp components: The first-generation Ford
Mondeo sold outside North America. It has glass outer headlamp lenses, but
there is a plastic *inner* lens as a part of the low beam optics. This
lamp was designed before ECE regulations contained specifications
regarding plastic headlamp lenses, and because it was not an outer lens
but rather an internal optical component, the maker (who is experienced
and established enough to have known better) decided no special
precautions had to be taken. Oops, no. There's still a thriving market for
replacement gen1 Mondeo lamps for that reason.

DS

 

[David Lee]

JohnR66 wrotet...

While driving today, I saw a Chevy van with the plastic headlamp lens that
had severe UV radiation damage. It was turning a brown color. No way could
usable light get through it. I've seen them a bit hazy and even yellowed
but never this bad. The drivers side lamp was not as bad, still a tan
color, but night driving must be a no-no with that van.

I assume that you must be writing from USA - is there no mandatory vehicle
testing in your country? In the UK all vehicles over three years old are
subjected to an annual safety and emissions test (MOT) and owners must be
able to produce a valid certificate before they can obtain a valid licence
disk for the year. This sort of damage would result in failure and would
have to be rectified long before it got to this state.

David

 

[Victor Roberts]

JohnR66 wrotet...

I assume that you must be writing from USA - is there no mandatory vehicle
testing in your country?

In the US it varies by state. I live in New York and our
cars do have to pass an annual inspection. Among other
things that check the brakes, tires, emissions, and make
sure that all the light are functioning. However I don't
know if they look at the transparency of the lens on my
headlamp assembly.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
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It may not be used in any publication or posted on any Web
site without written permission.

 

[[email protected]]

While driving today, I saw a Chevy van with the plastic headlamp lens that
had severe UV radiation damage. It was turning a brown color. No way could
usable light get through it.

Is it possible that it was done intentionally? You can buy "tint" in a
spray can for the purpose of making your tail lights much dimmer^W^Wlook
cool - maybe somebody applied some to the headlights.

Matt Roberds

 

[David Lee]

Matt Roberds wrote ...

Is it possible that it was done intentionally? You can buy "tint" in a
spray can for the purpose of making your tail lights much dimmer^W^Wlook
cool - maybe somebody applied some to the headlights.

Nah! BLUE would be cool - brown's definitely warm! ;-)

David

 

[Daniel J. Stern]

I assume that you must be writing from USA - is there no mandatory vehicle
testing in your country?

Many jurisdictions in the US have exhaust emission testing, but almost
none have any kind of technical/safety inspection.

DS

 

[Daniel J. Stern]

NHTSA/DOT isn't in the business of approving materials.

Incorrect. NHTSA sets forth requirements for plastic materials used in the
manufacture of vehicle lighting devices in 49CFR571.108 S5.1.2. This
section of FMVSS 108 incorporates amended provisions of SAE J576 ("Plastic
Materials for Use in Optical Parts Such as Lenses and Reflectors of Motor
Vehicle Lighting Devices"). Administration of these requirements is
handled by NHTSA through AMECA, the Automotive Manufacturers Equipment
Compliance Agency, Inc. Any plastic material used in an automotive lamp or
reflective device for the US market legally must be on AMECA's List of
Acceptable Plastics for Optical Lenses and Reflex Reflectors Used on Motor
Vehicles, as amended from time to time.

That list can be downloaded here:

http://www.ameca.org/guides/AMECA S...tics Optical Lenses and Reflex Reflectors.pdf

DS

 

[Don Klipstein]

Many jurisdictions in the US have exhaust emission testing, but almost
none have any kind of technical/safety inspection.

Pennsylvania and New Jersey have safety inspections. However, it
appears to me that all too many inspection stations will pass headlamps
and all other legally required lights if they work at all.

- Don Klipstein ([email protected])

 

[JohnR66]

A lamp could also appear very brown due to the combined effects of the
yellowing of the lens, and water corroding the reflector. There is a
very good chance the lamp that appeared very brown also had a
significant water intrusion probelm that has corroded the internal
reflector making the lamp appear worse than the driver side lamp.

Impact modified acrylic is usually accomplished through the addition of
rubber to the acrylic which makes the lens transmission lower and
slightly hazier than a polycarbonate lens. Also the impact resistance
is still nowhere near that of polycarbonate. For example plexiglass DR
which is the highest impact acrylic that altuglas manufactures has it's
izod notched impact at 1.1 ft lb/ in while general purpose
polycarbonate is over thirteen times higher at around 13 ft-lb/in. For
protection against debris impact the polycarbonate is far superior to
the acrylic.

Properly coated polycarbonate will withstand the UV radiation.

Thanks Boxamn and to all the others for the feedback.

UV degraded polycarbonate will have lost a considerable amount of its impact
strength. So, it makes sense to UV protect the PC lens so it is stronger and
remains stronger than acrylic.
John

 

[Daniel J. Stern]

Disagree.
Surprise!

What document do you derive the explicit requirement of having to be on
AMECA's list of acceptable plastics before it can be used?

Check NHTSA interp files for the last ten years. This is why Hella wasn't
permitted to market their "magic colours" aftermarket taillamps with outer
lenses of green, blue, etc. The lamps emit all the correct light colours
as required per function, but because there are (or at the time were) no
approved green or blue (etc) plastic materials on the list, NHTSA's Chief
Counsel said "No" to Hella's RFI. A similar thing happened with the
first-design Audi A8, which for one year only in the US was equipped with
rear combination lamps similar in design to those used in Europe: An
all-red appearance was achieved by using an outer lens of "rose red"
plastic and a green plastic balloon over the colourless bulb for the rear
directional indicators. Through subtractive filtration, this combination
produces amber light. However, at the time one or both of those materials
were absent from the approved-materials list, so to satisfy NHTSA's
"please knock it off" request, the rear directional indicator was changed
to a conventional red lens over colourless bulb, as a running change in
production.

The manufacturers in the US are responsible for self certifying their
components to the regulations.

Certainly, but remember, a great deal of the US regulatory give-and-take
of compliance and enforcement is achieved on a much less formal basis in
North America than in Europe. Frequently there will be dialogues,
sometimes extensive ones, between NHTSA and a manufacturer when some
aspect of a lighting device's construction or performance falls in one or
another type of grey area. Often, these dialogues are resolved informally
(e.g., NHTSA asks the manufacturer to change something and the
manufacturer agrees, without there being a formal recall, issuance of
interpretation or change to the regulations).

Are you saying that NHTSA physically pays and directs AMECA to certify
these plastics?

Oof...please don't feed me words, thanks; I just ate. *urp*

I stick by the statement that NHTSA operates as a rulemaking body, not
an approval body.

That is true *for the most part*; US auto safety regulations are generally
administered on an autocertification basis rather than a type approval
basis, but there are exceptions. How else do you explain 49CFR564?

DS