On 4/28/2012 11:59 AM, Tegger wrote:
....

By law, plastic headlight lenses must be coated with an anti-abrasion
epoxy. ...
....

Well, no, not quite...

NHTSA has a bunch of requirements that lighting must meet but they do
not mandate any specific material or manufacturing technique, only the
performance requirements the end product must meet.

There's a reg's that requires that _if_ a coating is used to meet the
performance standards (brightness, color, etc.) that that coating must
contain a UV-detectable component so that it (the coating) can be shown
to be present in the production products but there's nothing that says
if can make the specifications w/o a coating you have to use one for any
purpose. The practicalities are that coatings are needed to meet the
performance spec's but that's not the way the reg's are written.

The tests are multitudinous and detailed, particularly for color
matching. The weathering test is outlined as--

S14.4.2 Plastic optical materials tests. Accelerated
weathering procedures are not permitted.
S14.4.2.1 Samples.
S14.4.2.1.1 Samples of materials shall be
injection molded into polished metal molds
to produce test specimens with two flat and
parallel faces. Alternative techniques may
be used to produce equivalent specimens.
S14.4.2.1.2 Test specimens shape may
vary, but each exposed surface must contain
a minimum uninterrupted area of 32 sq cm.
S14.4.2.1.3 Samples must be furnished in
thicknesses of 1.6 ± 0.25 mm, 2.3 ± 0.25 mm, 3.2
± 0.25 mm, and 6.4 ± 0.25 mm.
S14.4.2.1.4 All samples must conform to
the applicable color test requirement of this
standard prior to testing.
S14.4.2.1.5 A control sample, kept properly
protected from influences which may change
its appearance and properties of each thickness,
must be retained.
S14.4.2.2 Outdoor exposure test.
S14.4.2.2.1 Outdoor exposure tests of 3
years in duration must be made on samples
of all materials, including coated and
uncoated versions, used for optical parts of
devices covered by this standard. Tests are
to be conducted in Florida and Arizona.

S5.1.2 Plastic materials used for optical
parts such as lenses and reflectors
shall conform to SAE Recommended
Practice J576 JUL91, except that:
(a) Plastic lenses (other than those
incorporating reflex reflectors) used for
inner lenses or those covered by another
material and not exposed directly
to sunlight shall meet the requirements
of paragraphs 3.3 and 4.2 of
SAE J576 JUL91 when covered by the
outer lens or other material;
(b) After the outdoor exposure test,
the haze and loss of surface luster of
plastic materials (other than those incorporating
reflex reflectors) used for
outer lenses shall not be greater than
30 percent haze as measured by ASTM
D 1003–92, Haze and Luminous Transmittance
of Transparent Plastic;
(c) After the outdoor exposure test,
plastic materials used for reflex reflectors
and for lenses used in front of reflex
reflectors shall not show surface
deterioration, crazing, dimensional
changes, color bleeding, delamination,
loss of surface luster, or haze that exceeds
7 percent as measured under
ASTM D 1003–92.

There are something like 300 pages of more fascinating bedtime reading
but the word "epoxy" doesn't appear.

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