I've never used one so I need some advice please.
Are they designed to fit over or inside my Gold Tip Carbon Arrows?
What has been your experience with them?
Where is the best place to buy them?
The least expensive I've been able to find is approx 13 dollars and that includes shipping.
Thanks for any help you can give me.

Nockturnals are less expensive and work as well....
Firenocks are better than Luminocks but more expensive...

The Lumenoks (and the rest of them as well) fit inside the shaft. Also, you can order them straight from the shop online.

They use a thin battery that slides inside the shaft before the nock pressure fits on. They will add a slight amount of weight to the back of your arrow.

Brother had to sand his down, not sure if this is required or not. Def a cool addition to your hunting game. He had Lumenoks.

The Lumenocks from my experience are too heavy. If you use them you must practice with them. They weight in about 20 gr more than you regular nock. This extra weight actually makes the arrow 'butt' heavy and your arrows will impact higher that with a regular nock. Substantially higher.
Nocturnaly on the other hand weigh only 20 gr. and are only about 7 gr heavier than your regular nocks. I've only shot these at 20 yds so far as I've just purchased them and they impact the same as the std nock. I purchased 2 packs so I will be practicing with them closer to season. Now what I must say here is that the ONLY reason I bought these is to be able to see exactly where I hit the animal and to find my arrow (or the animal) after the shot, especially in low light. A good hit or bad hit are good or bad no matter what nock you have on your arrow. The lighted nock helps the hunter to determine if you should track after a short wait or wait several hours. But my grandkids are in awe when I shoot my 'magic arrows'......