Aspherics, dome on or dome off?

I’m a little confused as to whether I should leave the dome on when using an aspheric lens. I don’t remember seeing this discussed and a quick search doesn’t turn up any threads, sorry if this post is repetitive.

My understanding (or misunderstanding) is that the dome focuses the light a bit, projecting the light forward (i.e. with and XP-G2 the viewing angle is 115 degrees with the dome on, dedomed it would be greater, say 145 degrees but that’s just a guess).
When using with a reflector this reduces spill and allows the reflector to focus more light forward into a tighter hot spot and more throw (assuming properly focused).

When using an aspheric lens though a wide viewing angle is not desirable as much of the light is wasted illuminating the inner side of the head and not well collected/focused by the lens.
If that’s the case then an LED with a much narrower viewing angle would be ideal for use with an aspheric lenses (similar to using multiple lenses?).

So why do so many people dedome their emitters when using aspheric lenses?

More throw.

Not enough 3G’s to load the thread, but LEDs & Other Stuff - (Reference Guide)
Has a lot of good info that might help you find what you are looking for. Iirc dedoming is down toward the middle or end of the OP.

This particular topic is over my head (I believe MEM would be most qualified), but here is how I understand it:

The dome has the effect of magnifying the die like a drop of water would (which i’m sure you know). When you dedome, the true size of the die is revealed. Even though some lumens are lost (including on the non-reflective walls of a zoomie) the surface brightness is still higher because you have ~80% of the lumens coming from a die image that is ~50% of the original domed image size. With both aspherics and reflectors, you want the highest surface brightness possible for the most throw. If the light is coming from a more concentrated spot to start with, then it’s easier for the reflector or lens to concentrate it more.

I remember reading a thread on it, but …

I think dedoming is less favorable with aspherics than with reflector lights or reflector/aspheric lights, because, as you said, there is a greater reduction in overall light output. However dedoming still increases the throw and warms the tint.