Headlight covers are aftermarket modifications made from a variety of materials (e.g., metal, polycarbonate, ABS plastic or self-adhesive vinyl film) which are applied over the headlamps of a new or used car in order to reduce the percentage of light transmitted, to tint the color of the light transmitted and/or to protect the lenses from stone chips, bug splatters, pedestrians and minor abrasions. 
Wartime Origins of Headlight Covers
During World War II civil and military authorities often enforced brownout and blackouts which restricted the use of lights on transports and passenger vehicles in order to make detection by aerial reconnaissance and bombers more difficult. Blackouts (turning off lights) and brownouts (limiting light emissions by way of hoods and masks) were enforced in cities and coastal areas as protection against the night-time aerial attacks in both Axis and allied countries. One of the first civilian examples of headlight covers was produced in NSW, Australia by the Read family dairy. 
The Evolution of Headlight Covers
The use of headlight covers and the modification of light produced by vehicles has continued into the present day in both the military's development of special blackout head and tail light technologies and in the civilian sector as well. In addition to headlight covers' use in light reduction they have also been employed to protect headlamps from damage in both civilian and combat environments. In fact, 3M now makes a wide variety of aerospace and military films solely for this purpose.
With time, however, the automobile industry began to take note of the protective benefits of headlight cover film and it was soon being employed by race car drivers despite the difficulty of working with the original films. According to Kay Lam, marketing manager for the automotive division of 3M “The first films were thicker and less compliant, [because] their purpose was to help keep...[surfaces] from eroding in the harsh, sandy environments to which they were exposed.” 
Legality of Headlight Covers
At present there is no national statute which governs the use of headlight covers. Most localities and municipalities will have laws which regulate the use of headlight covers and or tint and will specify the percentage of light that must pass through and/or the minimum distance from which a vehicle's headlights must be visible. 
- "Headlight cover". 2014. Retrieved 18 September 2014.
- "World War II headlight cover". 2014. Retrieved 18 September 2014.
- "3M Aerospace and Aircraft Maintenance". 2014. Retrieved 18 September 2014.
- "The Evolution of Paint Protection Film" (PDF). 2014. Retrieved 18 September 2014.
- "ARE BLACK HEADLIGHT COVERS ILLEGAL". 2014. Archived from the original on 6 July 2015. Retrieved 18 September 2014.