Bulbs that lasted longer burned less brightly.
The companies maintained that the thousand hour lifespan was a compromise between these two factors;
durability and efficiency.
The Phoebus cartel was ended by the war,
but Helmut has uncovered hard proof of planned obsolescence and others are investigating how it operates today.
I've come to meet Stefan Schridde at Berlin Technical University.
Stefan is studying build-in obsolescence in consumer goods and he's shocked by how pervasive it is.