Stimulation of target cells using light, e.g., in vivo or in vitro, is implemented using a variety of methods and devices. One example involves a vector for delivering a light-activated molecule comprising a nucleic acid sequence that codes for light-activated molecule. The light-activated molecule includes a modification to a location near the all-trans retinal Schiff base, e.g., to extends the duration time of the open state. Other aspects and embodiments are directed to systems, methods, kits, compositions of matter and molecules for ion channels or pumps or for controlling currents in a cell (e.g., in in vivo and in vitro environments).