2D Maglite and a dummy cell?
There are no stupid questions...
but there are dummy answers. 
My question is this:
Given that God is infinite, that the universe is also infinite and the speed of light is 299 792 458 m/s…
Would anyone like a toasted teacake?
Toasted teacake? Hmm… got any crumpets??
Ask me a question that is wholly unbready and not even slightly curranty.
I had a biophysics professor in college who was very fond of saying that any time infinity comes up in physics, it was natures way of telling you that you screwed up the math somewhere.
Does anyone have some good rule of thumbs on how many amps various LED’s typically pull in 1x18650 and 1x14500 lights?
Basically debating when to use higher amperage batteries (VTC6/30Q , Windyfire 14500) vs. higher capacity (NCR18650GA, panasonic 14500)
xp-g2
xm-l
xp-l
xp-l hi
xhp 35 hi
xhp 50
etc…
why li-ion cell is 3.7V, but not 3v or any other voltage?
Some people do have infinite egos though.
Difficult to answer because there’s more variables than you mention here (spring bypasses?, length/thickness of led wires?, low or high drain batteries?, old produce XP-G2 or new produce XP-G2?)
Personally, for every build again I look at the led test data, the battery test data, and at the components that I will be using, and then I do the calculation.
Why are there almost no protected flat top 18650's?
I've only been able to find one, at an online vape site with no real assurance of it being genuine.
To be “protected”, you need the board on one end, usually the negative, and the sense-strip running to the positive end. To secure that strip at the positive end, you need a cap on top of the nekkid positive terminal, and usually that’s with a button-top cap.
Most are double-wrapped, with the sense-strip running between the 2 wraps, others like the panny-B just have Kapton tape covering the strip, which is then visible.
Most probably figure that if you’re sticking a cap on it already, you might as well make it a button-top so it’ll look like conventional cells and fit in holders, etc., without the need for nipples, springs, etc.
18650 batteries are made as flat tops because they are almost exclusively used in battery packs so a tab must easily be welded onto it.
Protected 18650’s are for a niche market that the producer never intended, protection therefore is always added as an aftermarket process by a different manufacturer.
I think button tops are added then because they are more versatile, and there are not many devices that exclusively work on flat tops.
Anyone knows if this is available in black? Convoy tube holster (tan)
i only know THIS one
Yep me too but apparently this just came out. But a pity i dont see it offered in black 
Tennergy made what could be considered protected flat tops ...
My guess on why 3.7 volts is because nimh and nicad etc are 1.2v and three cells combined equal 3,6v which if I remember correctly was a number more commonly used than 3.7v. I'm sure there is a better answer ..but hey "there are no stupid answers "
Candela and lux. How can they be simply explained to an idiot? (me)
I guess it can 
Take a look on these threads I was also inspired by the mod in the first link, so I made mine (2nd link)!
My turn for some “stupid” questions 
1 - Are there “ready to use” lighted forward clicky switches? If so, where can I find them? 
2 - How good can a triple 14500 (XP-G2, 15mm or 17mm MTN DD driver) flashlight be? Is it too much for a 14500 cell, even with small “turbo boosts”? :question:
3 - Is there any slim flashlight head (ex: Thorfire TG06, or similar) that possibly fits the body of an Astrolux X5? If so, which one?
Thanks in advance for eventual answers to these questions