I find a "tactical" light nearly indispensable, even in the daytime. I'm always finding myself looking for something in some dark corner or under something. Sure I could use my phone, but (and I'm no engineer) my feeling is that the light on your smartphone was meant to be a camera flash, designed to be on for only milliseconds at a time. It doesn't have the element, circuitry, or the heat sinking to be on for extended periods of time. Using your phone instead of a dedicated light is false economy. I wouldn't want to burn up my thousand-dollar phone just because I was too cheap or lazy to carry a small EDC light.
For $50-60$ you can carry an excellent light that will give you years of service from companies such as Fenix, Streamlight, FourSevens, and others. Or if you have the scratch, it's hard to go wrong with a Surefire. I carry a FourSevens Quark Tactical 2 AA model. It's a discontinued older version, but they catalog something similar with less programmability (which I never use anyway) and about 100 lumens more. I also carry a Quark Atom keychain light (also discontinued) that puts out a whopping 30 lumens max, but it's perfect for reading menus or getting keys into locks and the like.
Here are more ways a dedicated light beats a phone:
1) A light can be used as an impact weapon or compliance tool ( think kubotan). Try that with your smartphone.
2) A person walking through a dark parking lot shining hundreds of lumens in dark corners and adjacent parked vehicles looks switched on (pardon the pun) and aware. Someone doing the same thing with a phone just looks like every other jamoke with a phone.
3) I can't recall ever hearing about someone getting jacked for his flashlight. I wish I could say the same about smartphones.
There are plenty of reasons to carry a light and very few good reasons not to.
