At Philips, he did research on lighting systems, especially gas-discharge lamps. Later he was appointed professor of applied physics at Eindhoven University of Technology, leading the Atomic Physics group, mainly researching gas discharges and plasmas.
- PhD dissertation at Utrecht University: Kruithof, Arie Andries (December 12, 1934). "Aanslag van het waterstofmolecuulspectrum door electronen". (under Leonard Ornstein) (in Dutch)