Well the spill shape is also different depending on bezel used.
addtion to point #7 - there's a price, there's quality
Additional comment.
11) People do weird stuff to their lights. Where else will you find instructions on cooking your light?
Great post! This needs to be sticky'd!
Trooplewis, can you and other people who have knowledge of why 18650's and other batteries are dangerous posts the do's and don'ts.
Lothar you beat me to it!
It should be a sticky. Simple stuff, but very useful!
Nice one Troop!
Marc.
Well , not all hosts are equal ...(p60)
Past a certain point - quality does not really improve that much , in fact you can pay more , and get less [ yes you can ]
For a long time Surefire owners tried desperately to put down the P60 clones [ Solarforce comes to mind ] , but these days they have pretty much given up , some have even gone out and purchased the Solarforce host after resigning to the fact its a hell of a clone for the money ..
Are all P60 clones equal = No , just depends on what is important to you ..
The largest source of issue could be the clicky , this is the Achilles heel of cheap lights [ clicky switch ] , so chose wisely ..
2011 saw a marked increase in the overall quality of budget lights , but the Ca-vet Emptor still applies [ buyer beware ]
Lights
Single cell lights = Thumbs up , not much to watch for here , except shorts ... [ Buy a Multimeter ]
Multi cell lights = Match the cells - For capacity - Discharge capability - and test often for matched discharge [ batt voltage should match ]
Batteries ,
Discharge capability is often linked to temperature ... Warmer = Higher discharge
What to watch out for = Overcharging [ dont get excited till you go over 4.25v ]
Over discharge = try to hit the charger before going bellow 3.5v [ performance really drops off at 3.5v so why go there ? ] I aim to charge around 3.8v to 3.9v
If you discharge to 2.5v , get it in the charger as quickly as possible , maintaining very low voltage for a long time damages the battery
Charging :
Watch battery behaviour , and learn ... [ variable depending on individual charger ]
What to watch = Termination voltage , voltage sag after charging ..
If you have a hobby charger , discharge the cell to test capacity ...
Even cells that can hold 4.2v after charging can degrade and lose a lot of capacity ..
trooplewis is talking about the same P60 drop-in, used in different hosts.
old4570, is there a link to explaining the above. I'd love to know more and know why it damages the battery.
Is the "don't use below 3.5V" only for high mode, or medium and low modes as well. Why?
So 18650's are only useable from 4.2V to 3.5V
Basically it is the drop-in (i.e. the combined emitter/driver/reflector module) that defines what the beam will be like. Meaning that if you put the same P60 drop-in into any host then you'll get the same beam.
Learn about lithium ion batteries and understand that not all batteries are created equal. Know that with the exception of a few higher end brands, almost all 18650s over-rate their capacity just as most budget lights over-rate their lumen output.
Learn what the protection circuits do and why you want one on your batteries.
Know that overall output does not equal throw and that just because one light has a higher lumen rating does not mean it will out throw another with a lower rating.
Not all emitters even within the same bin are going to be exactly alike. A quick tutorial on Bins can be found here.
Also keep in mind that different bins will have different color temperatures or tints and that the same lumen will appear different to the human eye depending on that tint. Colors referred to as warm can be thought of as being mixed with yellow (2700k incandescent is an example) while tints referred to as cool can be thought of as mixed with blue (5500k cfl). Knowing which tint you prefer will help you select the proper emitter bin and make you happier with your purchase.
i.e. At least to my eye a cold tint (T6 cool white) appears brighter than a t5 warm white when put in the same body with the same drive and same cell.
Every drop-in I've purchased included the reflector. Doesn't matter which p60 host you put the dang thing in, you get exactly the same beam. Every time. AN expensive host is a joy to hold and behold, but my $85 Pelican host throws the exact same beam as my $8 Ultrafire host when I swap the drop-ins between the two. LOL, someone mentioned the bezel of the host may change the beam. That is true, it will 'scallop' the edges if it has a crenalated bezel, but the beam is actually the same, your host just cut part of it off.
14) Be aware that claims of 1000-1400 lumens from single cell 18650 flashlights are bogus! Ebay and many Chinese web sites claim these numbers, but they are almost always off by a factor of 40-50%. The very best lights, like a TK41, can manage 800+ lumens with EIGHT AA batteries, and that thing is a hundred bucks. You are not going to get 1000 lumens out of your $25 Ebay light, but that does not mean it won't be the brightest light you ever bought. Prepared to be amazed, but not 1000 lumens worth of amazed. Remember, in comparison, your Dad's 2 x "D" cell Maglite put out about 29 lumens.
15) Many inexpensive torches have PWM. PWM stand for Pulse-width modulation, it is basically a cheap way to obtain Medium and Low modes. It isn't necessarily a bad thing, unless the PWM is very slow, in which case your eyes may detect it as "flicker" or a fast strobe. Members here detect PWM by holding a flashlight in a dark bathroom, and then waving their arms around with it in the shower. Get used to the idea, flashaholics are strange people.
Be aware that every light you order will be about half as big as it looks online.
Great source of information for everyone just starting out and some who have been around for awhile.
Thanks
This is exactly the experience I had when I got my first SF P60 host. I looked huge in the picture and got me thinking for a while before ordering because I was worried about the 'large' size. 
Great thread, it deserves to be stickied for all new flashaholics to read.
Great post. I wish I would have had this when I was getting started. I still have lots to learn. Here is another thing that a new guy needs to know.
Double the lumens doesn't mean that your light will look twice as bright. Generally speaking, everything else being equal, you will need 4 times the lumens to notice twice the brightness. For instance, to notice twice the brightness of a 100 lumen light you will need somewhere around 400 lumens.
Another thing I have found. Just because your light has the newest emitter like the XM-L, doesn't mean it is a better light. I have found that many lights work better with XP-G or other older emitters. Most often I have found that the smaller the reflector, the better the older emitters seem to work. For instance. Shiningbeam makes a S-mini light that you can buy with either an XP-G or you can buy it with the newer and more expensive XM-L. The XP-G is listed at 360 lumens and the XM-L is listed at 400 lumens. I own both and in real life I much prefer the less expensive and older XP-G version. It doesn't have quite as much spill but it seems brighter and has a more useful beam IMHO. Bryan at Shiningbeam feels the same but he makes the XM-L because people want the latest and newest technology available.
Great guides trooplewis, this thread will definitely shows a path for the new flashaholics! I become a flashaholics for almost a year until now. When I started collecting and looking for flashlights I learn everything one by one in CPF and of course here in BLF. I used to have so many questions in my head and then I slowly understand them by looking at these threads. So, this is the way I gain my knowledge.
To the new flashaholics: BLF is such a resourceful place to learn about flashlights!
LOL +1 on that. My girlfriend still cannot accept the fact that I always purposely went out at night and keep shinning my flashlights on some distance buildings... 
LOL +1 on that. My girlfriend still cannot accept the fact that I always purposely went out at night and keep shinning my flashlights on some distance buildings... 
That is the coolest part of having a good flashlight
Great Post, Troop!
8 ) There is no such thing as that one, perfect flashlight. If there was, I would gladly pay $500 for it and stop buying flashlights, but it does not exist.
I don't believe that for a minute! 
To paraphrase the Notorious B.I.G., number 10 should have been number one to me.
Budget lights are cheap in terms of bang for the buck (ie. value), but in the long run you'll probably be spending at least as much on cheap lights and accessories as if you were buying reasonably priced brand name lights (not überrarium custom lights). The difference is you'll probably have more fun.