tl;dr: it doesn't work
A quick heads up: apparently
UIScreen.wantsSoftwareDimming doesn't work on iOS 7, the iPhone 5S, or both. I was unable to detect a difference in the brightness levels no matter what that setting was at; previously you had to set that flag then adjust the brightness to make it take effect. (I've always felt that LCD brightness levels have a narrow dynamic range. At night I often want the screen dimmer. In bright sunlight, I want it brighter.)
Looks like I will be reactivating my alpha overlay to support ultra-dimming. People need to sleep after all.
This blog represents my own personal opinion and is not endorsed by my employer.