Surefire x300 Ultra
It projects 500 lumens of light, which would light up a room and can illuminate up to 40 metres of space ahead of you.
It has a flick switch on the bottom to turn on and off, and a handy little button feature which allows for temporary light when one doesn’t want to give away their position. You would push the bottom in for the light to turn on, and then release and it automatically switches off.
The Surefire x300 provides a minimum of 1.5 hours of constant light, when turned onto its ultra light setting. The light is waterproof, and though not shock resistant, can withstand a certain amount of misuse.
The Surefire 400 is essentially the same type of light as the 300, but comes with the added feature of a red laser pointer. This is quite a handy feature, and designed with high visibility in mind.
The downside to this upgraded version is of course the price. The Surefire x400 can range between 400-600 dollars brand new. This is quite a jump from its predecessor, though the extra feature may be too good to ignore.
If simple is what you are after, the x300 is the safest option, and the x400 designed more for rifles and high calibre weapons.
The light runs for a minimum of 1.25 hours at full capacity, and is waterproof for up to 30 metres. This is one of the most reliable brands, and, when treated properly, will almost certainly last years. Insight is the leading manufacturer of weapon lights, and supplies the military with lights. This particular product is cheap, putting you back between 100 and 200 dollars.
This particular light is also very agile and lightweight, and, similar to the Surefire, will fit nicely onto your weapon without messing up your aim.
Depending on your price range, geography and desire for quality, the two brands listed are the best options. They are the two leading manufacturers of weapon lights, and should both be considered before purchasing.