I have read somewhere that motion on TV is really a series of still pictures presented very fast in succession but forgot the minimum number of still pictures / second to just allow us to perceive motion. What is that number? I also realise that power supplied to our homes is in the form of AC and at 50Hz where I live. Meaning tha the current varies in direction 100times a second. When such a current powers a lamp in my home, I don't detect the light flickering which I should had the AC frequency been much lower. I wonder what is the minimum frequency at which flickering can just be not seen and continous illumination is perceived. Would the two frequency numbers in the two questions equal each other?