In the 1970s, William M. C. Lam (1924-), one of the most committed advocates of qualitatively orientated lighting design, produced a list of criteria, or rather a systematic, context-orientated vocabulary for describing the requirements placed on a lighting system. Lam distinguished between two main groups of criteria: the "activity needs", which are the needs resulting from performing activities within a visual environment, and the "biological needs", which sum up the psychological demands placed on a visual environment and are applicable in every context.