I am more into the tactical applications of lights. The way I see it is, if you have a question about your car, ask a mechanic...your health, a doctor...flashlights, you guys on this forum.
Anyway, what I'm taking away from this post so far is that it depends, am I right? Let me phrase it like this...lumens is the measurement of the total amount of light produced at the source right? And I know that a lot depends on the reflective cone, but are there manufacturing specs to look for that would indicate the likely amount of projected light? Is candle power a unit of measurement when it's an led light source.
From what I understand, 2 lights can be 160 lumen, but not project the same amount of light? Also, I've heard that "splash back" on white surfaces isn't an issue up to 1000 lumens. Is that correct, because I'm looking at some 500 lumen lights, but I don't to f my night vision up during a room search?
Lumens is the total amount of light being sent out of the flashlight.
Think of it as so many gallons per minute of flow out of a hose.
You can let the water pour out of the garden hose into a bucket at say 1 gallon per minute, or, put your thumb over the end of the hose, and squirt that gallon per minute into the bucket....its still a gallon per minute, total.
The throw of the light is measured in terms of cd...the same as the lux at one meter.
Generally, the higher the cd, the tighter your thumb is on that hose spray....for the same total flow rate/total lumens.
The cd is measured at the hot spot...the central brightest part of the beam. Surrounding the hot spot is a corona, a bright donut of slightly dimmer light than the hot spot. If light missed the reflector, so it never got focused, it just spills onto the ground, and, is called "the spill".
So, lumens is the total flow of light. LUX is the light that bounces back so you can SEE the target. You can't see lumens, what you see is what they bounced off of, illuminating the target.
The brighter the target looks, the higher the lux on it.
The tight thumb spray might make a very small circle of light on the target, a small, tightly focused beam angle.
A giant fire hose might have an opening as large as your fist, and spray the water further than the teeny tight stream past your thumb on the garden hose. It has more gallons per minute to work with.
So, for the same beam angle, a light with more lumens will typically have a LARGER hot spot...and perhaps a larger corona too, more spill, etc.
For shooting in darker conditions, you typically need 1 - 2 lux on your target to aim/track well. Some people need more, and if you have no night vision at all (You burst into a dark warehouse from being outside all day in bright mid-day sunlight...)...you typically need a LOT more than that.
As for "Splash back"...that's just talking about the glare of your light bouncing back too brightly. The more dark adapted your vision, the easier that is to happen. The tighter your beam angle, the more likely that is to happen.
The tactical issues really depend on the context.
For example, for that warehouse, if you are bursting in and might be facing return fire, you need a light that goes OFF instantly...typically with a momentary on type switch...so it goes off when you let go, or just needs a single click, depending on what you're used to/can do under pressure....so you can turn off your bullet beacon.
If you burst in, and have a tight beam, you must quickly scan around the entire space as though you are looking through a paper towel tube...you only see a little dot of light at a time of what's out there.
If you have a floody beam, you can burst in and its like all the lights went on, and you see everything at once...including the positions of the potential targets/shooters, people running for cover, etc.
If you are standing next to a bunch of buddies, that floody light will also tend to show all those bad guys where your buddies are, etc. unless you are in front enough to not also light them up too, etc. (IE: You ALL pop and move if that's the case...)
The 1,000 L rule of thumb is meaningless in practice, as the range, the cd of the light, the reflectiveness of the background, your level of night adaptation, etc, will change all of that.
So if you storm the warehouse and its 1,000' to the back wall, your light needs a cd of ~ 100,000+ to get some useful targeting lux on targets.
(The square root of the range in meters = the cd needed to get one lux on the target)
So, indoors, under the above scenario, a 500 lumen light with 100k cd will barely put a small dim spot of light on your target. A 1,000 L light will definitely still not be too bright, and so forth.
If its not a warehouse, its a 10' x 10' room, sure, 100k cd is going to glare. (Its not the LUMENS that glare, its the cd/lux)
For example, an ordinary 75 watt light bulb in an small table lamp puts out about 1,200 lumens...with a very low cd.
Few people would say a small table lamp makes a room too bright...in fact, most rooms use a few lights so its not too dark, etc.
If bursting into the warehouse/room and some one hitting the light switch for a table lamp would incapacitate the entry team, ok, fine...its too bright....but that's not normally the case.
Now, if you're asleep and its 3 am, and you turn on that same table lamp...yeah, it will seem very bright, and you might need a few seconds to adjust....and, the process of adjusting is degrading your night vision.
It takes a while for your vision to adjust in either direction, so, if doing a night sortie sort of thing...there is a RANGE of adjustment depending on where you are/what you're doing before hand.
Me, I prefer FLIR for all that...but, for flashlights, you choose the tools for the job...and sometimes you want more throw/less flood, and sometimes you want more flood/less throw.
