BU06:Research
From 2006.igem.org
[http://partsregistry.org/Featured_Parts:Light_Sensor: Light Sensor Parts] and [http://www.nature.com/nature/journal/v438/n7067/full/nature04405.html: paper]
It seems to repress gene expression by having red light inhibit phosphorylation which would activate a promoter. I don't understand how pops affects this at all...