Fact #1 -

Before the 1980's, vehicle headlights were made of glass.  In the late 80's, car manufacturers began to design cars with much more aerodynamic designs.  Polycarbonate plastic was designed, and used to create headlights that were very strong, durable, easily molded and much safer than glass. 

The problem with polycarbonate plastic, is that it is very porous, making the lense extremely vulnerable to the elements.  A protective coating is applied to the lense, which has UV inhibitors to keep the plastic from deteriorating.  Without proper care, the protective coat will eventually fail and deteriorate.  This is what causes your lenses to flake and oxidize, yellow, get cloudy and hazy, and in some cases loose up to 70% of their overall visability and performance.

 Fact #2

All automotive lense manufacturers apply a protective-hard coating on the polycarbonate factory lenses to protect the plastic from deterioration and damage.

If the hard-coat is not reapplied, it leaves the lens vulnerable to the sun, rain, snow, salt, and debri.

Fact #3

  According to Maryland Law, in order to pass the Maryland State Inspection, headlights are required to have a certain amount of candle watt power and clarity.  If one or both are impaired due to being oxidized and deteriorated, the car will not pass inspection

Fact #4

Be careful when buying new lenses.  Not all new headlight lenses are the same.  Lower priced lenses sometimes have a very distorted light pattern, and sometimes have a very weak protective coating.  This weak coating causes the lense to deteriorate very quickly.

 Fact #5

 Some used lenses may look good, but may have cracks, and the adjusters for the alignment may not work, due to previous accidents or even just sitting outside for long periods of time.