#AnsweringBack – Why is there a mirror on an headlight beam tester?

During a weekly drill-down into our web-page we came across an interesting query which forms part of a new series of blog posts where we “Answer Back” – The question posed for this blog post was;

“Why is there a mirror on an headlight beam tester?”

Here is the answer…

In order to measure the headlamp pattern accurately it is imperative that the measuring device (the headlight tester) is positioned so that the optical head and target are exactly normal (90 degrees) to the position of the physical headlight bulb. In simple terms this ensures that the beam pattern falls directly onto the measuring target…

In order to achieve the most accurate measurement there is adjustment that allows the headlight tester to rotate side to side about its pivot point until the correct position is achieved – the mirror allows the inspector to check the accuracy of this “rotational position”.

The mirror is actually used as follows…

The inspector looks into the mirror and picks a point on the vehicle which is symmetrical along the centre-line e.g: the top left and top right of the windscreen; the left and right hand side of the vehicle grille etc.

The mirror has a series of lines which run across its width and the inspector uses these lines to judge when the headlamp assessment tool is parallel to the vehicle. Once the inspector is happy that this is the case he can “lock off” the unit so that it cannot move from the selected position – the headlamp tester can then be rolled along its rails to the position in front of the headlamp beam for the actual measurement to be conducted.


A better solution, such as with a GE5418L is to eliminate the mirror from the headlight tester and replace it with a laser. This significantly reduces the “judgement” that the inspector needs to apply as the laser is mounted to the testing unit such that the laser line can be clearly seen on the datum points selected (i.e the windscreen or vehicle grille).


Here is a video of the GE5418L in action – look for the laser line on the front bumper of the vehicle and how it is used to adjust the position of the headlight tester to ensure it is normal to the bulb…

The GE5418L can be purchased online from just £676.80 + VAT delivered for you to fit yourself or £995 + VAT including fitting and a 12 month re-calibration contract. To buy online you can visit the product page for this headlamp tester which is : http://getech.org.uk/Product/HeadlightTester/ or for more information you can contact GETECH direct on 0844 800 9785 during normal office hours.

For more information on GETECH call during office hours, visit http://getech.org.uk or mail info@getech.org.uk.


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