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.
I offered selling custom made lights with neutral and warmer tints as a flashaholic usually prefers. None sold. Everybody asked for the cool blue- white beam instead. Neutral is usually a rarety in flashlights. It is always a plus if a flashlight has an option for tint.
Throw works similarly to perceived increase in overall output even thought the two aren’t related.
As mentioned to perceived twice the output it actually needs to be four times brighter. With throw the lux (brightest part of the hotspot) needs to be four times greater for twice the throw.
You increase throw by increasing the surface brightness of the emitter and by increasing the diameter of the optic/reflector.
XR-E is generally the emitter you want for throw if you are looking for absolute throw. If you are really looking for decent throw with a larger beam then you may go to XM-L with a larger optic/reflector.
Finally useful spacing in brightness modes seems (to me) to be X 3 as in 10 lumens…30 lumens…90 lumens…etc… Lumens being a measurement of the overall output of the light.
ROFL :bigsmile: Perfect flashlight with XM-L, perfect light with XPG, perfect P60 light with SMO... :bigsmile:
Nice post, mate ;)
I love # 15 LOL :-)
#16 The flashlight beam consists of the hotspot which is the brightest center part. This may be well defined in a SM reflector light or diffused by a OP reflector light from the same emitter. Around that hotspot is the corona which is also sometimes called spill.
#17 A good "thrower" flashlight for 1 man is useless to the next man. Some people love a laser/pencil thin beam because it projects light only on the exact spot that you point it at and there is little to no backscattered light from the spill around the hotspot. This is typically users who like the higher contrast that this gives plus if it is from a no spill light and the object you shine the light on is far away it does not kill your night vision. The most extreme pencil beam lights are aspheric lens lights. Others prefer a light with varying degrees of spill because they need to light up the area around the object being examined or even to navigate through the terrain to get to it.
If you are in doubt about which type of light you like and dont mind using a little dough and time to find out before you buy bigger and more expensive lights here is my short list of tried and tested (by me) lights for that purpose.
Aspheric light would be : Sipik SK68 which is 9,20$ at dealextreme for 1 mode that takes both AA and 14500 li-ion and comes in either black or grey.
and then a P-60 host such as the Ultrafire WF-504B with a XML 5 mode drop-in also at dealextreme which comes in black or grey too. ~ 21 $
Then a XP-g drop-in so you can compare the smaller output but longer runtime and different beam profile with its smaller hotspot and less bright spill. Also from dealextreme. ~ 11$
And last a 1 mode XP-E R2 drop-in which is the most throwy dropin for the P60 format. This should set you up for some fun times and the options of changing the reflectors around on the drop ins. Also from Dealextreme. ~8~$
For this you would also need to buy at least a pair of 18650 batts and a charger. These come recommended ( by me because I have them and they work) and are protected. ~10~$
# 18 It is much cheaper to buy more batteries of lesser capacity and then swap them in your lights than it is to buy high capacity ones. ( $/mAh)
# 18 Chargers come in all sizes and prices. I recommend the XTAR chargers based on my research from reading the tests some of the more knowledgeable members make. I have the Xtar MP1 myself and have the Trustfire TR-003 on the way because I bought so many batteries lately. They both come recommended by those in the know. Xtar MP1 is ~25 $ and the trustfire is ~18 $
Now that you have so started your deroute you might as well add these 3,7v li-ion 14500 batteries to drive that little Sipik SK68 at the power it is meant to be :-) ~ 6 $
# 20 Cylindrical Li-ion batteries (and batteries in general) are measured by their diameter followed by their length and given a numerical suffix of 0 (zero) to indicate that they are round. So a regular AA battery would be a 1,5V 14 mm by 50 mm round battery and thus a 1,5 V 14500 battery. So a 18650 is 18 mm diameter 65mm long and round.
If you just added all of the above to your cart you might as well throw in a C8 style light to really see for yourself how much a bigger size reflector does for throw. And you should be set up for ~100 $ if you chose the Trustfire charger. Not bad all things considered :-)
If SWMBO nags you about this then say it is all for (pseudo) science LOL
PS: Can someone proof read this (not grammar/spelling) but fact about batteries and such. I am tired after a few hectical days and should have been to bed hours ago :-)
EDIT: I've edited out the misinformation about battery nomenclature - Thanks to Agedbriar et al. for the help :-)
i guess the number 1 of the list that you shall put is "FLASHLIGHT IS HIGHLY ADDICTED"
I seem to remember reading that the last digit stands for "battery shape", with zero meaning "cylindrical".
I don't think that flattop/buttontop execution is evident from the battery type code, but I may be wrong.
I believe agedbriar is correct.
I've edited the post :-)