iPhone 11 bottom lens functionality

I am not sure if this question has been asked earlier.

Everyone knows iphone 11 has 2 lens on the back. I have been curious how these two lens work, as I covered the bottom one the picture is not affected. Of course if I cover the top one the picture is all dark.

So does anyone know if the bottom one is really used. I didn't find any detail from internet.

[Re-Titled by Moderator]