Headlights that are clouded or yellowed from aging reduce lighting by more than 80% causing hazardous nighttime driving conditions, according to a new research report from AAA.

With up to half of all crashes occurring at  night, headlights are a vehicle's most basic safety system. However, sunlight damage to the protective plastic coatings on headlights can cause discoloration that diminishes their capabilities. 

The research finds that deteriorated headlights, when used on low beam, generated only 22% of the amount of light that a brand new headlight does when operating at full capacity.

According to the report, headlights can begin showing signs of deterioration between three and five years. The authors note that replacing headlights with original equipment manufacturer parts is the most effective method to restore light output back to 100%.

Replacing headlights with aftermarket parts performed adequately, restoring light output between 83 and 90%. However, aftermarket parts may provide less intensity and more glare for oncoming drivers.

Restoring headlights versus replacing them is the most cost-effective option. The report emphasizes that both professional and DIY restoration restored light output to a sufficient 70%, yet produced more glare than is acceptable according to Department of Transportation (DOT) criteria.

To conduct the research, AAA used an accredited laboratory to test headlights from two popular sedans, approximately 11 years in age. Results from the degraded headlights were measured against new headlights to quantify the amount of light produced for each. All testing was done in accordance with the Federal Motor Vehicle Safety Standard 108 as set forth by the DOT.