Oh, great. Way to pop my balloon…
I will now sit and await the heat-death of the universe.
As said, as efficiency nears maximum theoretical, heat will stop being a limiting factor, and battery power will be the bigger limitation.
Therefore, if battery technology sees more rapid imprpvements, flashlights will follow.
Having said this, I don’t think there will be another huge jump in technology like there was in the first decade of the 2000s, more evolutionary and slow steps, as it has been pointed out.
The MPG illusion is interesting, and it is distantly related to one of the issues with using lm/W to measure efficiency.
Fuel consumption in the United States is measured in miles per gallon (MPG), while most of the world uses liters per 100 km. Most people will only be familiar with one or the other. You can use both to measure fuel consumption, but they are not the same. MPG naturally makes people underestimate the efficiency improvements on the low end and overestimate efficiency improvements on the high end.
And so it is.
I agree with that, and with most of whatever is below. :-)
That’s what I was thinking. At high output levels the efficiency of an LED drops a lot. If they can figure out a way to not let that happen, we could have lights with 2-3x the output whilst using the same power. Imagine a 25000 lumen EDC! 
Strange to see these comments about LED’s limiting out on output and efficiency. I have been thinking about this too from a noob’s point of view. I look and try to understand Lumens, KCD, CRI, etc… and will continue doing this with 3 lumen tubes, 2 light meters, 3 dmm, etc… because I love this hobby and everyone here at BLF.
.
But one thing I use to judge is the simple eye test. Thanks to Matt’s video, I came to a decision not to mod a light to the new 90.2 led because I like the 70.2 better. I know the numbers say different, but pictures seem to show different too. So I am most likely wrong about the 90.2 and I am going to get a kit from TA and put it in a light, this will most likely be the only one. So it does appear to me also that leds are near their max performance. You have to admit they are quite impressive and the variety suits many different needs.
.
.
XHP 70.2
.
SBT-90.2
.
The lights I use most often only clock in at about 100 lm/W (XP-L HI) or 70 lm/W (219B) with a linear driver. And, of course, that number drops when the lights are in really bright modes. It’d be really cool to have lights which get 200 lm/W instead, without sacrificing beam quality.
For me, the biggest win there is the increased runtime. Lights could run for a really long time between charges, and this would be especially important for small lights with 14500 / 16340 / 18350 cells. It’d be nice to get output and runtime on those similar to what we get from 18650 lights today.
Higher turbo modes would be fun too, though I feel like lights have already gotten brighter than I really need. I use a D4 a lot, and it can do over 4000 lumens… but I rarely ever want more than 100. So instead of a high-power quad, I’d mostly be happier with a more compact light with a single LED and a driver which runs very efficiently at low modes.
That might all be limited to 2X or 3X remaining improvement, but battery tech could go quite a bit farther. They’ve been working on a couple new types of cells, each one a huge upgrade from what we’re using today:
- One type changes the internal structure of the cell. Instead of a coiled roll of materials, it changes to something like a 3D checkerboard pattern. This increases the charge and discharge rate dramatically… like, by a factor of 1000+. Today’s high-amp cells may be able to start fires in under a second, but that pales in comparison. Instead of 20 Amps output, it could do 20,000 Amps. It’s not an exaggeration to call it an explosive level of power, considering it works in the same way as gunpowder. I don’t need or want that much power in a flashlight, but it does have a really nice benefit — extremely fast charge times. Instead of hours, it could charge in a minute or two.
- The new battery tech I’m most excited about is … wood. They’ve been developing cells which are, basically, rechargeable wood. The benefit of this is that it increases energy density by about 7X. So, instead of a 3000 mAh 18650 cell, it could be a 21000 mAh cell. Great for extending runtime and/or greatly decreasing the size of a light without decreasing the runtime.
Combine that wood battery with a 2X more efficient light, and it could be a 14X increase. That would mean a tiny 16340 or 14500 light in the future could compete with today’s 3x18650 lights. A little S-Mini or AA-sized light could make as many lumen-hours as a SP36, D18, or ROT66. Basically, look at the runtime of any current light, and add a digit… and that’s what we might be carrying around someday.
So… even though the LEDs themselves are running out of room to improve, the future of torches still looks pretty bright for another decade or two.
UVC LEDs have recently progressed quite a lot, moving from fancy pricey curiosities to possibility of practical (but still quite pricey) applications. They made major strides in both mW/W efficiency and total mW per LED that will sooner or later allow them to displace existing UV lamps.
I think that slow progress in Led industry is good for flashlights. Without new led and
without the ability to write larger numbers on boxes flashlight manufacturers would have to think about convenient UI, quality of spot, quality of light and so on.
I’m not following the latest developement but last time I checked, searching info about Soraa Vivid technology, it seems to me that the researches were gradually switching to laser based lighting for better efficiency that is more free of current droop. OLED panel might improve for diffuse lighting sources and laser for concentrate lighting sources.
In the future, your flashlight will be linked to eye-tracking. So you can light up a huge space with a narrow beam that rapidly scans across the scene to match where your eyes point. To the operator it will seem as though he has an infinitely powerful flooder.
You only see sharply in a small area of your eye called the fovea centralis. To take in a scene you scan your eyes around rapidly, 3-5 times a second.
In VR there is the concept of foveated rendering. The eyes are tracked and only a small portion of the scene - central in your gaze - is rendered sharply. Everything else is rendered at low-quality.
It can work with a flashlight also.
It is intended merely as an example of how there are many inefficiencies in the field of flashlights. So even when we hit the limit of LED efficiency, there will be other things to work on, such as how efficiently we direct photons towards what we are looking at.
In automotive there’s scene detection already.
ToyKeeper
On the throw side of the equation, do you think we can get much past the mile mark?
Yes, but low quality do not mean useless. Absence of peripheral vision called tunnel vision it is disease.
I hope you are not writing this as if tunnel vision is a negative property?
In some governmental professions this property is mandatory 
Eye-tracking flashlight would be great for someone with tunnel vision
Yes it is negative property. You can ask some one with this disease.)
Great topic. All technological developments reach plateaus. There are limits in physics where LED’s are concerned, somewhat analogous to the sorts of limits that CPU efficiency & performance has faced—heat. And while you can have active heat reduction systems, they cause notable battery drain. Heat build-up is what keeps an LED from being able to throw for long periods. Take for instance the FW21. 10,000 lumens! But, it lasts mere seconds.
Now there’s LEP… which produces less heat. It’s of course a very focused beam, but aside from producing a hybrid flashlight (adds LED’s for spill), maybe there’s some innovation with optics to be had. Something better than your typical “zoomie” approach.