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To ensure adequate visibility without excessive glare, vehicle headlights are designed to use a specific source of illumination. The optical designs of headlights gather the luminous flux produced by the light source to produce a useful beam pattern that meets the relevant requirements and standards for vehicle forward lighting. With the advent of solid state, light emitting diode sources for general illumination, an increasing number of LED replacement headlight bulb products has emerged over the past decade. In most cases, these LED replacement bulbs are not permitted for legal use on public roadways, but some countries have begun to permit specific LED replacement bulbs to be used legally on the road for specific makes, models and production years of certain vehicles. If they can be demonstrated to produce a beam pattern that meets the photometric requirements for a legal headlight, they are permitted to be used legally for on-road use.

Flashing warning lights and vehicle markings of various colors are used on a wide range of emergency and other service vehicles to help inform drivers about the presence of these vehicles and the types of situations that drivers are approaching. Although not applied consistently among all jurisdictions, the colors and performance of these visual elements are often selected to help communicate the type of scenario (such as red flashing lights to indicate an emergency vehicle, or yellow flashing lights to indicate a non-emergency service vehicle). Previous investigations have shown that flashing light colors, vehicle and marking colors, and flashing temporal characteristics (e.g., rapid versus slower flashing) can all affect a driver’s perception of whether a vehicle along the road is responding to an emergency situation or not.