A headlamp tester, also known as headlamp aligner or beam setter, is an instrument to check both the orientation and intensity of a vehicle

headlamp A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term for ...

beam to ensure that it meets a minimum standard for the country of use of the vehicle. In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

, a headlamp beam tester is used to assess the headlight during a

MOT test The MOT test (or simply MOT) is an annual test of vehicle safety, roadworthiness aspects and exhaust emissions required in the United Kingdom for most vehicles over three years old. In Northern Ireland the equivalent requirement applies after ...

but in order to be used it must be approved as suitable for use in the scheme. A list of acceptable headlight testers for use within the

scheme is listed on the

Department of Transport The Department for Transport (DfT) is a department of His Majesty's Government responsible for the English transport network and a limited number of transport matters in Scotland, Wales and Northern Ireland that have not been devolved. The d ...

website. A headlight tester comprises a fully adjustable single optical

collimated light A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction pr ...

lens assembly which is typically mounted on a vertical column or rail. The assembly is adjusted vertically to the actual height of the headlamp, which is typically around 500mm for passenger vehicles, but can be significantly higher for heavy goods vehicles (HGVs). The

optical lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a #Compound lenses, compound lens consists of several simple lense ...

itself is designed to focus the

pattern on a screen. At the top of the lens mounting column is typically a

mirror A mirror or looking glass is an object that Reflection (physics), reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the ...

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...

which allows the headlight tester to be aligned with the longitudinal axis of the presented vehicle. During a headlamp inspection, the vehicle headlamp is aimed through the

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

, projecting the headlamp pattern at an aiming screen target which has lines showing the desired headlamp pattern. For low beam, this pattern is symmetric for the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, asymmetric for the rest of the world. The screen will either be adjusted for, or directly show, the percentage of downwards aim of the headlights. The aim will be as low as 1% for passenger cars, and can be as high as 4% for HGVs. The aim, horizontally and sideways, can be adjusted by adjustment screws on the headlamp mounting assembly. A feature often included as part of such a tester is a method by which the intensity of the beam can be measured. This is achieved with a

light meter A light meter is a device used to measure the amount of light. In photography, a light meter (more correctly an exposure meter) is used to determine the proper exposure for a photograph. The meter will include either a digital or analog calcul ...

Lux meter A light meter is a device used to measure the amount of light. In photography, a light meter (more correctly an exposure meter) is used to determine the proper exposure for a photograph. The meter will include either a digital or analog calcula ...

which is incorporated within the assembly itself. This can be used to not only measure the intensity of the dipped beams but also to measure and compare the full beam intensity.

References

{{Reflist, 30em Motor vehicle maintenance