Tina Jørstian and Poul Erik Munk Nielsen, eds., Light Years Ahead: The Story of the PH Lamp, Copenhagen, 2000, pp. 155-56, 162-63 for similar examples
Erik Steffensen, Poul Henningsen, Denmark, 2005, p. 57 for a similar example
Gorm Harkær, Kaare Klint: Volume 1, Copenhagen, 2010, p. 400