I am not sure how well it works yet, but it works in trivial cases i.e. a 40 W lightbulb and my fridge (once I had stopped stray morning light).  I am going to ask my neighbours if I can pop the Photo Diode on their meter as I don't want to stop the one that is already logging mine. What would be good is if others, who have a lot more knowledge and skills than me (I am really just a chancer than fiddles about till it seems to work) could improve and add to it. Things that would be nice