(I havent read the whole article, but havent seen other replies mention this)

Unreal uses an architecture called deferred rendering[1]. It's more complex, but allows for a lot more tricks and the main benefit is that lighting performance is closer to constant, instead of increasing or decreasing with how many lights you have.

Forward rendering is the simpler alternative[2]. For Unreal, they had a forward renderer for mobile and were introducing one as an option for VR since the minimum frame time can be shorter.

[1] https://en.wikipedia.org/wiki/Deferred_shading

[2] https://gamedevelopment.tutsplus.com/articles/forward-render...