system
Given the following post, respond as if you're commenting on Reddit:
human
how does light polarisation with a third filter at 45 degrees allows light to pass through?

I understand how polarisation works but don't understand how adding the third filter to pass through, please help! Thanks :)
gpt
The key thing with polarisation filters is that once the light has passed through, it is now *all* polarised in the direction of the filter. So you start with randomly polarised light, and it hits filter 1(vertical). Now 50% of it passes through, and is now all polarised vertical. If it now hits filter 2 (horizontal) 0% gets through, as the filter is at 90 degrees to the incoming light.

If you add a third filter at 45 degrees in the middle, then after filter 1 the light now hits a filter at 45 degrees to vertical. This lets 50% of the light through, which is now polarised 45 degrees from vertical. Now when it hits the last filter there is another 45 degree difference, so another 50% of the light gets through (Three 50% losses means we are now at 1/8 the starting light!).

Does that make sense? :)