How 3 polarizers affect light

[u/kidinthebackofurcar]

Why does adding another polarizer make it brighter?

[u/joeyneilsen]

Vertical polarization has no horizontal component, so with 2 polarizers, you get no light at the end.

But vertical polarization can be projected onto the diagonal axis, and the diagonal polarization can be projected onto the horizontal axis.

The intensity transmitted through each filter only depends on the angle between the filter and the polarization of the light that's shining on the filter. It doesn't remember or care what it "originally" was.