The decision on the headlight ventilation system of the BGH (X ZR 16/17) makes clear the principle that the state of the art cited by the patent must be taken into account when interpreting a patent claim. If, in the description, a known prior art is equated with the preamble of a patent claim, the features of the characterizing portion are not to be understood, in case of doubt, in a manner that allows to find them in the prior art from which they are meant to differ.

The plaintiff was sued by the defendant from of the patent in suit and again filed a nullity action. The BGH's decision rejects the plaintiff's appeal against the dismissal of the nullity action. The patent in suit concerns lighting and signalling devices in motor vehicles, in particular headlamps with a ventilation system. Specifically, according to the invention, the ventilation system is of interest, which is to be improved over conventional ventilation systems according to the state of the art cited in the patent.

The patent in suit is distinguished from the quoted state of the art by the fact that a labyrinth with a double change of direction is formed. A document cited in the patent in suit already reveals the generic term of patent claim 1 and, accordingly, does not show the double change of direction.

The problem here was that a twofold change of direction could also be seen in the aforementioned cited reference. There is an additional change of direction between the air inlet openings and the inlet duct. However, since the patent in suit attempts to distinguish itself precisely from this document, further requirements are placed on the change of direction in the interpretation. Thus, the labyrinth is only formed beyond the air inlet behind the inlet duct.

In this way, the BGH makes it clear that the quoted state of the art can be decisive for the interpretation of the patent claim. An explicit equation of the state of the art with the preamble of the claim may lead to the patent claim being interpreted in such a manner that it cannot be disclosed by the cited state of the art. The objection of lack of novelty from this prior art is therefore not possible without further ado. However, this also leads to a narrower interpretation of the claim, which must be taken into account in an infringement litigation. It can also be assumed that a subsequent inclusion of an acknowledgment of the state of the art can be problematic with regard to an impermissible extension of the protection conferred.