I am confused with how "Ambient Display" and "double tap to wake" works

I am fairly new to HTC/sense and I am confused with how the "ambient display" and the innate double tap to wake function works. I am currently on LeeDroid rom but I assumed that both the LeeDroid and stock rom share the same function. So far, when i disable "ambient display", my phone will not light up when I get a text. I can't find an option to disable/enable double tap to wake. Here is what happens on my phone (I do not have pattern/password/fingerprint to unlock)

1) phone screen is off --> Double tapping on the phone wakes the screen up. Phone lights up with lockscreen.
2) phone screen is off --> doing a 1 finger swipe up motion on the screen wakes the screen up AND unlock the screen, taking me to the unlocked homescreen.
3) phone screen is off --> finger on fingerprint sensor wakes screen up. Phone lights up with lockscreen.
4) Phone screen is off --> phone just lights up randomly (I didn't even move the phone or change the lighting in the room) with clock in upper screen with a black background. (similar to the screen you get when the screen lights up with a new text notification). Is this the "ambient display" screen?

I am very confused as to which of those are part of the "ambient display" function. Why does the phone light up randomly? How do I disable "double tap to wake" or "swipe up to unlock" functions?

Thanks. Any help is appreciated

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