If they can get a square (rather than rectangular) sensor, and if my math is right, it's a lot less than half.. A circle has an area of pir^2. And it fits just

If they can get a square (rather than rectangular) sensor, and if my math is right, it's a lot less than half.. A circle has an area of pir^2. And it fits just inside a square whose sides are length 2r, and whose area is thus (2r)^2 or 4r^2. Therefore, the circle fills pi/4 of the square. So only 21.5% of the pixels are wasted. It gets worse if they use a rectangular sensor, though. With a 4:3 rectangular sensor, it's 41.1% wasted. For 3:2, it's 47.6%. And for 16:9, it's 55.8% wasted.