The inflicted light stress resulted in carotenoid production by the cells. As shown by Lamers et al. [6] the carotenoid producing phase starts almost immediately after applying stress. Within 9 h it reaches the maximum productivity. As noticed earlier (unpublished results), when not applying a turbidostat regime to maintain a constant stress per cell, the stressed cells grow in size so that self-shading results in a lower light perception and consequently the cells can ‘grow over’ the stress and start multiplying again. At the point where this happened (approximately 24 h after the start of stress) we started the turbidostat.