Constitutive (tetR) lacI-production (lacI+LVA) to block promoter (lacI+pL) in ground state of a 2-state system. lacI+pL can be activated, e.g. over IPTG, thus leading to the production of GFP (green fluorescence). This device allows to estimate repressed (lacI) activity/full activity under ITPG absence/presence.