I've decided to buy a SIGHTMARK Photon RT 4.5x42 Digital Low Light Scope for use on my AR rifle to shoot hogs at my farm at night.  I have a open field next to the house where hogs come in frequently at night and where I can shoot out to 200-230 yards.  I chose the SIGHTMARK Photon scope mostly due to economical price and positive reviews I've read.

The question I have is the difference between 4.5x42 and 4.5x42S.  From what I can see the only difference is the IR illuminator.  The 42 has built-in 940nm IR illuminator where as 42S has built-in 850nm IR illuminator.  I believe 940nm IR illuminator has shorter range but is less likely to be detected by hogs while 850nm IR illuminator has longer range but is more likely to be detected by hogs.  Is that right or are there other differences between these two?

No experinece with the unit. You are correct that the 940nm will be less visible. In terms of range it depends on where the sensor is actually sensitive. For regular NV you would be correct, but digital CCDs may have different sensitivity in those parts of the spectrum.

The Attached IR is good for maybe 75 yards max, with a full moon.
Your best bet is to get the cheapest Photon scope and a more powerful external IR, and hunt them from further away with less chance of spooking them.
Also get a PVS-14 shuttered eye guard and slip it into the eye guard of the Photon.
That'll keep your face and background from being lit up when saddling up to,or backing away from the scope.

This video does a pretty good job of explaining the S vs non-S models.

X2 to everything he said.

What's a decent IR illuminator for use out to 200 yards without breaking the bank?

This one worked very well for me.  I actually bought my scope from the cowboy guy in the video.  He might work you a deal on the illuminator if you bu it and the scope as a package.

https://outdoorlegacygear.com/products/ultimate-night-vision-20ir-illuminator?variant=42383728853

Thanks for asking this question.
I had wondered just how strong the red glow is from the S unit, but have yet to see any images of it. Has anyone else seen it in person or found an image of the glow online?

It's noticeable if you're looking for it.  Most hogs don't notice it. I never really cared. It was the last thing every hog I shot got to see.

So since my post got buried without reply a few weeks ago...

How high are y’all having to mount to clear the A2 FSB?

I asked this a few months ago and what I remember seeing what people said was that it'll just blur like any other optic behind A2 fsb. Problem though is where you mount the IR illuminator. If you put it on the scope the IR light may bounce off the rear of the A2 sight and right into your Photon.

Photon + A2 sight is a non-issue.  Mount the external IR at 3, 6, or 9 o'clock and you will have no problems.  Personally I like 9 o'clock because I'm right-handed and can punch the thumb switch easily with my support hand.