How Many Screens are there in the World?

Here's my crack at estimating the number of screens in the world. We know the worldwide population is roughly 7.5B and I estimate average household size is 3.5  which gives us roughly 2.1B households in the world. The average US household has roughly 2.9 TVs on average, but the worldwide average is closer to 1.83 TVs per household so let’s say there 3.92B TVs in the world. Add to that roughly 2B smartphones, 1.7B computers and probably a half a billion tablets and we are looking at over 8 billion screens.