De doming ? what does it do ,can someone clarify

[DrJones]

Flashlight Optics - Dome, Dedoming and Throw

I wanted to write a longish text about flashlight optics for quite a while now, starting with all the optics and photometry basics, up to the details of what throw depends on and why, including how dedoming increases throw, all with a coherent line of argumentation and some experiments to try. I even started writing that document, but it seems I just don't find the time to finish it in reasonable time. I now decided to take a shortcut and just do a very short version of it, especially focusin…

It does neither widen nor narrow the beam of the LED itself significantly.
It reduces the total output (luminous flux) a bit, since the dome helps to get the light out of the die.
However that reduced output is coming from a smaller apparent area (since the dome created a magnified image of the die), so the illuminance (surface brightness, some kind of brightness density) is higher, and that allows a more intense focusing of the beam with a reflector or lens, thus gives a narrower beam with more luminous intensity (candela) and throw.

Edit: I'm afraid that TEEJ quote has some flaws.