Lighting

by Daniel Stern
European-code headlamps have had a sharp cutoff at the top of the low beam for many decades. Prior to the mid-1950s, it was a symetrical flat-across cutoff. Performance comparisons with the American sealed beam, carried out in query of whether it should be adopted in Europe, revealed that while the U.S. headlamp produced levels of glare considered unacceptable in Europe, it also gave substantially longer seeing distance down the nearside.
As a result, the asymetrical cutoff was introduced: flat on the offside, rising to the nearside at a 15° angle.

This greatly increased seeing range on the nearside while retaining the strict control of glare of the previous horizontal-cutoff beam pattern. Some years later, bright French and English minds devised a variant on the asymetrical cutoff, which was subsequently added to the applicable ECE regulations: a stairstep-shaped cutoff consisting of a nearside horizontal cutoff at the horizon, connected to the offside horizontal cutoff below the horizon by a 45° line segment. Commonly known as the “Z-beam”, it gives a substantial seeing distance advantage compared to the 15° upsweep cutoff. It’s also easy to make compatible with the SAE photometry required in America and satisfactory to American performance preferences. And yet it never really caught on in Europe.
There were a couple of Z-beam headlamps commercialised, such as the very good 180mm (7″ SAE-fitment) H4 unit produced by Valeo’s Cibié operation in the 1970s and ’80s, and the Lucas works in England also worked keenly on the Z-beam, with their development led at the time by Geoff Draper, now chairman of GTB.