Because bad things often happen after dark, our rifle needs a light to help us positively identify things. There are a few important considerations with lights. How do you attach a light to the gun? Where do I attach my light? How much light do I need? How will I activate my light?
You need to mount your light solidly so it will not come off when you need it! Typically, the light is mounted to either a handguard or rail. The light may have an integral mount or it may require a mounting bracket depending on the maker. For a basic rifle with no handguard or rail mount option an inexpensive solution is the front sight tower mount, visit Brownells.com.
If you have a rail or handguard that allows you to mount a light you will typically mount it in the 12:00, 3:00 or 9:00 position depending on your preference and the activation system the light has. I prefer 12:00 as it is directly in line with the bore of the rifle.
A tactical lights relative power is measured in Lumens. Generally, the more the better, especially with rifles which have a much longer range than handguns. We need to see to shot AND to see where our rounds might come to rest. Two hundred lumens is a good minimum to consider when light shopping.
Every light has a different activation system. I prefer a toggle or push-button system operated by my off hand thumb or fingers. One system that has largely fallen out of use that was formerly quite popular is the tape switch where the light is activated by some sort of pad from the pistol grip. The systems were a pain to route, secure to the weapon and added a layer of unnecessary complexity.