When people think of police equipment, flashlights probably aren't the first things that people think of. People probably think of firearms, handcuffs, radios, tazers, etc
But, lights are important tools that all officers carry. Officers work shifts, which means that half the time they are at work, they are out in the dark. When you are working nights, you'll be going to calls in areas that will be treacherous- back alleys with needles and broken bottles on the ground. Up a flight of stairs in a dark exterior stairwell on the way to a rooftop, etc...
My point is, you need to be able to see where you are going. It's important to make sure that you aren't stepping anywhere treacherous that could cause you to slip and fall and hurt yourself. OR, stepping on some crucial piece of evidence while investigating a call.
When you are assigned to a call, you want to make sure that you do your best to investigate it, but be mindful that there is no such thing as "going" to a routine call. Anytime you attend a call, there is the potential that you make discover it to be a serious incident where evidence must be preserved. You never know what you are going to uncover until you get there. The last thing you want is to walk over an entire trail of blood and kick a murder weapon down the alleyway just because you couldn't see in the dark.
If you are in a foot pursuit chasing a suspect in the dark, or searching for evidence in a field at night, you are going to require a quality, reliable light source.
I believe most, if not all departments provide their officers with good quality lights. It's also a good idea to have a backup in case you are out somewhere and your bulb burns out.
There are several quality brands, but I personally like surefire lights. They build solid and durable units, and they are VERY bright. One of their lights, I think it's called "The lawman" is 750 lumens. That is BRIGHT!
Take a look at the video below. They compare 3 different brands, including a Surefire flashlight. The Surefire is easily the best light, and the one in the video is 200 lumens. Imagine what the 750 would look like!!!