A newby to the AR world but enjoying gaining the knowledge from those with experience.

If you are looking to add a light to your shooter is it better to mount it on top of a scope or in front of the handguard??

Will one of those mountings create a problem for using the scope with some glare???

You want the light on the handguard side or bottom forward of the scope.

I shoot right handed, so I like to operate my lights on an AR with my left hand thumb.

However on a 16" carbine with the regular front sight I have a light mounted on the sight triangle on both sides. I operate one with the thumb, and the other with my left had
trigger" finger.

On some of my bolt action and drilling hunting guns, I have the SureFire light mounted on top of the scope as there are no Pic. rails in these rifles. I have shot pigs at night with this set up with excellent results.

Not as ergonomic at the AR set up but works good for hunting.

There are several locations, lights and mounting solutions out there that work very well. What type of AR? What is your purpose?

I have a Sig M400 enhanced carbine and the purpose would be for a combo of home/camp nighttime defense and some short range varmint hunting.

You need to play with placement, feel it, work it. If a SD rifle walk your home halls with it in various positions and see what is most comfortable and provided you best sight picture picture for your conditions. This will vary shooter to shooter.

Very personal decision.

right next to the kitchen sink, toilet, and bathtub

While we're at it....
Does it matter which side the coffee grinder goes on and should I balance it with the can opener?

Jim