Earlier this year in Teva Pharmaceuticals USA v. Sandoz, Inc., 135 S. Ct. 831 (2015), the Supreme Court changed the appellate standard of review for claim construction decisions. The Court held that while claim construction is a legal question reviewed de novo on appeal, any underlying factual findings based on extrinsic evidence are reviewed for clear error. Since the decision, commentators have speculated about the significance of the Teva decision and the impact it would have on claim construction decisions in the future.

We now have a prime example of the kind of case in which the new standard of review will be outcome-determinative. In last week's Lighting Ballast Control LLC v. Phillips Elecs. N. Am. Corp., No. 2012-1014 (Fed. Cir. June 23, 2015) decision, the Federal Circuit applied the new standard of review and reversed its prior ruling. This decision makes clear how important expert and inventor testimony will be under the new claim construction standard of review announced by the Supreme Court in the Teva v. Sandoz case. Additionally, by emphasizing that the extrinsic evidence did not contradict unambiguous claim meaning that was clear from the specification, the Federal Circuit made clear that there are limits on the use of extrinsic evidence in claim construction.

At issue in Lighting Ballast was the meaning of the claim term "voltage source means." Based on testimony of the inventor and a retained expert witness, the district court determined that the term did not warrant means-plus-function treatment under 35 U.S.C. § 112, ¶ 6 because one of ordinary skill in the art would understand the term to mean "a rectifier, which converts alternating current ("AC") to direct current ("DC"), or other structure capable of supplying useable voltage to the device."

On the initial appeal, the Federal Circuit applied the de novo standard of review, reversed the district court's claim construction ruling, and held the claim indefinite based on the lack of corresponding structure in the specification. On rehearing en banc, the Federal Circuit affirmed the panel decision. Lighting Ballast Control LLC v. Phillips Elecs. N. Am. Corp. 744 F.3d 1272 (Fed. Cir. 2014) (en banc). Following the Supreme Court's decision in Teva v. Sandoz, the Supreme Court remanded the case to the Federal Circuit. On remand, the Federal Circuit held that the district court correctly relied on extrinsic evidence to understand the disputed claim term and that its factual findings as to the meaning of that term were supported by testimony from the inventor and the expert witness. Accordingly, because the extrinsic evidence was not used to contradict claim meaning that was unambiguous based on the specification, the Federal Circuit affirmed the district court's judgment.