How to turn off the animation when locking screen on Nexus 5 running on KitKat?
As pointed out by a comment on the question itself: GravityBox, a module for the famous Xposed framwork, can be used for this (and for many other things: it's a feature-rich toolbox): you can select a different effect, or even switch it off.

If you're on a custom ROM, however, the dev doesn't recommend using GravityBox, as it might lead to conflicts (many of the tweaks GravityBox offers are already present in custom ROMs). In that case, simply search the repo for other CRT related mods – there are several of them dealing with this. One example would be XBlast Tools, which explicitely mentions: CRT Screen off effect (No Effect,Horizontal Effect and Vertical Effect) in its list of tweaks.