Any light attached to a shotgun, or a .44mag revolver, or a rifle, or a larger cliber, 45-70 would be the best bear round imo.
Slugs or buck?
Thanks to all for all replies, actually I wasn’t expecting so many replies regarding bears on a technical forum like this :). There are some areas in my country where brown bears live and I wonder how I would react if I ever met one. But it turns out noise is more useful than light on bears. They don’t have good eyesight anyway, so this is logical.
I like the “Party Mix”. Load them Buck, Slug, Buck, Slug, Buck, etc…… OR vice versa.
Also relevant: [Article] How Fast Can A Bear Run?
Sounds like running from a bear should be your last resort.
Bear spray, bells, air horns, or whatever might help.
But as alpg88 said, have whatever light you have attached to a 12 gauge shotgun, big bore rifle or handgun.
Know how to use it & cut loose if need be.
Short barrel 12 gauge with the slug/buckshot “party mix” is hard to beat.
As a logger, I’ve lived and worked in both grizzly and black bear country for roughly 50 years. On Afognak Island in the Kodiak group, I had to walk roughly 3/4 mile back and forth from my cabin to the camp to meet the crew bus. I carried a shotgun with heavy loads but never needed to use it. I sang all through my walk(Mr.Bojangles mostly). Bells would probably have worked too but might not have scared a bear as badly as my singing. My point being that you need to let bears know you’re coming. They don’t want to be seen and they certainly don’t like being surprised. Make noise frequently and the chance you’ll ever need to use armament is minuscule.
You don’t have to outrun a bear. Just ensure you always travel with someone who runs slower than you. :sunglasses:
And be sure you can also run…faster than that dear’s calf (1m08s) or than the bisons’ (4m03s):
Stand up, arms over your head, and make noise. Yell. Bang on a pot if you have it.
The best use of the flashlight in this scenario is to illuminate your path as you move away from the bear… slowly if the bear is not charging, fast as you can if the bear is charging. 
Here’s an oldie but goodie……
So are you recommending that if attacked by a 3/4 ton Kodiak bear you should club it with your 6D Maglite? :person_facepalming:
Clearly the 
denotes a serious and solid recommendation…
Whichever LED you are using, make sure to de-dome it. Then you’ll have a bare emitter. Sorry.
This is unbearable
confabulation:
I find Mules easier to use than Bear Emitters,
Just give the Mule to the Bear, and let Him eat it, instead of Me having to eat the Mule.
To use Bear Emitters, I have to break the glass first, and I might not have the Presents Of Mine, when my Flight or Flight Instant kicks in… 
Whatever mode the weapon light on my 458 SOCOM is on.
This is what I meant. Silly answers to a silly question. Nothing personal.
Bears can attack you even if you are holding a machine gun, let alone a flashlight.
Who said anything about a machine gun?
Tail light.
Thanks for sharing your expertise. Yours is the voice of experience.
I've also done my share of singing when hiking alone in bear country.
One time while descending Maggie's Peaks at Lake Tahoe, I found fresh bear skat on the trail every two or three hundred yards. None of it had been there earlier in the day. Dusk was approaching, so I figured the bear was coming down the mountain just ahead of me.
For the last mile and a half, I sang just about every song I knew. I mean, I sang loud. The last bit of excrement was in the parking lot at the trailhead, only 50 feet from my car!
Never did see the bear.