Claim Construction – a lightbulb moment

On 31 July 2023, Zacaroli J handed down judgment in the Patents Court in Heraeus Noblelight Ltd v First Light Amps Ltd [2023] EWHC 1950. Hereaus was successful in showing that its patent EP UK 1 598 845 UK was valid & infringed by First Light.

In many ways, the case was unremarkable – a classic patent action with familiar arguments about claim construction and obviousness. But what makes it more interesting is how the judge approached the question of purposive construction and equivalents. There is also a second point of interest about the application of the principle that no cause of action arises where the infringement is only de minimis.

Facts and background

The patent claimed a method for sealing the ends of quartz glass tubes used in the manufacture of arc lamps. The judgment explains that quartz glass arc lamps generally consist of a hollow cylindrical tube filled with gas. Inside the tube at each end is an electrode, fed by a wire (usually tungsten) which passes through the ends of the tube. When an electrical charge is passed through the gas, it forms a plasma and emits light. The lamp must be hermetically sealed to keep the gas inside, which process can be done in a number of ways, depending on the type of lamp.

This case concerned only those lamps that use a “rod seal” method. This involves the electric current being carried by a tungsten rod inserted into each end of the lamp, around which is attached a thin sleeve of sealing glass, the middle section of which is worked up to form a “bead”. The bead is then fused with the outer glass tube of the lamp so as to form a hermetic seal. The size of the bead was central to the question of infringement. The claim was essential to an improved method of manufacture. It had a limitation that the bead should not be bigger than the external diameter of the end of the tube. First Light’s manufacturing process as described in its product or process description (“PPD”) used a bead that was bigger than said diameter by 0.1mm, with tolerances +/- 0.2mm.

Purposive construction and equivalents

Heraeus put its case as follows;

1) On a purposive construction, “not bigger” than the outside diameter of the tube meant “not bigger by reference to tolerances that formed part of the common general knowledge”, alternatively “not bigger such that it impairs the strength or utility of the seal“. Accordingly, even if a lamp was made strictly in accordance with the PPD it infringed the Patent.

2) Although the PPD specified the use of oversized beads, in fact – due to inadvertence, not a deliberate choice – beads used sometimes had a diameter no bigger than the outside diameter of the glass tube. This was referred to as the “literal infringement” case. [this basis is relevant to the de minimis point discussed below]

3) A lamp manufactured with oversized beads infringed the Patent by the doctrine of equivalents.

Hereaus said “not bigger” was a “fuzzy” limit, meaning effectively not “materially bigger” – materiality was to be defined either by reference to being within accepted tolerances, accepted by the experts to be within the CGK, or such that the strength or utility of the seal was not impaired.

On point 1, the judge found that the protection sought in the Patent was not limited to a method in which beads are precisely no bigger than the outer diameter of the tube, but included variants in which the bead is not materially bigger than the outside diameter of the tube to an extent “which could have no material effect upon the way in which the invention worked“. He adopted that phraseology from what Diplock LJ said in Catnic Components Ltd v Hill & Smith Ltd [1982] R.P.C. 183. That meant not bigger so that it impaired the strength or utility of the seal. As a matter of fact, that encompassed any bead made within CGK tolerances. The judge said that if that is wrong, then alternatively the phrase was to be construed as not bigger by reference to CGK.

Readers will no doubt pick up that a test “which could have no material effect upon the way in which the invention worked” is markedly similar to the first Actavis question on equivalents;

“(i) Notwithstanding that it is not within the literal meaning of the relevant claim(s) of the patent, does the variant achieve substantially the same result in substantially the same way as the invention, i.e. the inventive concept revealed by the patent?”

Catnic Components was of course the case about door lintels and whether the defendant’s product, which was a few degrees off the vertical, was nevertheless “vertical” within the meaning of the claim. It is interesting that Zacaroli J felt able to find infringement by adopting the purposive construction test that predated the introduction of equivalents. On the facts of Heraeus the parties agreed that there was no material difference between a purposive construction and equivalents.

De Minimis infringement

In view of the finding of infringement above, the judge did not need to determine this point, but he chose to do so in case of any appeal. The Claimants argued that effectively they need to show only one instance of infringement, with questions about “how many” left over for the subsequent form of relief. They relied on one particular sample.

The defendant on the other hand contended that this was not sufficient to establish the case although it was a necessary pre-condition. They said it would also be necessary for Heraeus to show that, on the balance of probabilities, when First Light’s operatives inadvertently made a product with infringing beads they did so more than a de minimis number of times. This argument had previously been approved by Arnold J (as he then was) in Napp Pharmaceutical Holdings v Dr Reddy’s Laboratories (UK) [2017]. In answer to a submission that a defendant who sold 200 patches that fell within the claim would undoubtedly infringe, and that it made no difference if the 200 patches constituted a single hour’s production out of a year’s worth of production, Arnold J said:

“I can only say that I disagree. It seems to me that most people, and specifically the skilled person, would be very surprised by the proposition that selling products only 0.01% of which fall within the claim constitutes patent infringement, particularly where the 0.01% are randomly distributed among the remainder. I consider that this is precisely the kind of situation covered by the de minimis principle.”

Zacaroli J delicately steered a middle course in this case, saying that the true position lay between the respective parties’ submissions. He said that where (leaving aside the purposive construction case) the only basis on which it was alleged that infringement occurred was due to the inadvertent failure of First Light’s employees to follow the manufacturing process, there will have been no infringement unless this has occurred on a more than de minimis basis. Accordingly, it was not sufficient to establish infringement that the sample in question was made with a bead no bigger than the outer diameter of the tube; it must be shown that this was an example of something that happened on a more than de minimis basis. Equally, it was not enough to avoid a finding of infringement that the sample did not infringe the Patent, if it could be shown on the balance of probabilities that undersized beads were used on a more than de minimis number of other occasions. He decided on the evidence presented that the correct application of the de minimis principle in this case meant that the sample in question did not infringe. However, as noted above, this did not affect his findings of infringement on purposive construction and equivalence.

If this point had mattered more (it didn’t because of the earlier finding of course) then many (the writer included) would likely have felt considerable sympathy for Heraeus, who were in a tricky position securing the evidence they would need. The claim was to a method (process), not a product, and it can be a lot harder to secure evidence when the process is being undertaken in premises to which there is not ready access, which is almost always the case. Although the judge recognised this burden, he nevertheless decided that the one sample shown was not enough to find evidence of infringement of the process. There was no evidence to show how often the process being undertaken led to the production of infringing samples.

The application of the de minimis principle in this way does seem to blur the clear position that the question of how many infringements is something for a damages enquiry, always accepting that here the claim was to a method not a product. The extent to which defendants seek to use it will obviously depend on the facts of each case.