What happens when pixels cover almost all the area of the sensor?

Question

I think, in this question, one who give an answer has to consider 'pixel size vs pixel pitch'.
I read that in some sensors, pixels don't cover the whole sensor and my question is, when the pixels cover almost the entire area, will the pixel size and the pixel pitch be equal?
And what can be said about sensor that is related to pixel size and pixel pitch?

Answer 1

With conventional CMOS sensors the issue isn't so much the spacing between photosites (pixels). It's all of the circuitry on top of them (usually on the edges of each photosite) that blocks light from getting through to the semiconductor layer. What microlenses do is redirect light that would otherwise fall on the edges of photosites where the circuitry blocks some of that light and aims it to the center of the photosite where there is no circuitry etched on top of the semiconductor layer.

By redirecting the photons that would otherwise not make it down a pixel well the microlenses help make the sensor more efficient because more of the photons that strike the sensor actually make it down a pixel well and are counted by the sensor.