…… 
“We shouldn’t expect too much, I think.”
Yer right. High expectations is the mother of all disappointment. Just ask my wife.
I think it’s fine to EDC a light that overheats quickly on high. Just as long as the light also has lower output modes that won’t overheat and give longer runtime.
Sometimes I want a burst of light to show off to friends or illuminate something very brightly. Other times I want sustained light that will last a long time without overheating.
There’s no reason, I can’t get both kinds of output from the same light.
Design can only buy you so much. Bad design can let the LED cook in it’s own heat before the body gets too warm. Cooking your hand is a harder issue where design smacks a wall. The wall is the need to get the heat out of the light itself. Once a good thermal path spreads the heat through the body of the light it’s done it’s job. If you are stationary or only moving slowly the primary way heat gets removed from the light is liquid cooling - blood circulating through your hand. Increasing surface area through design (fins etc) for radiation and convection only buys you a little in those cases.
That leaves some choices:
- Limit the drive current for a lights highest level. We tend to not like that answer as light freaks…er afficianados.
- The major design choice is to add more thermal mass. The light gets bigger and heavier and the same amount of energy heats it less. If you are exceeding the capacity of the light to dump energy that just delays the inevitable. Bigger and heavier buys more time before burning your hand but doesn’t prevent it if you run long enough. It may delay the issue long enough you can effectively ignore it for your normal runs but the core issue is still there.
- You can also have the light automatically ramp down by time or with a thermal sensor. We see that in some non-budget lights. That’s just another way of turning down to a lower level before it cooks.
Super high output with the LEDs we have now is going to have heat issues. They may be hidden by having enough thermal mass we can ignore the issue almost all the time. We tend to like small and bright so I doubt you’ll stop seeing light like that coming to market. 
Well if you were simply Not given the turbo option (so you only have low and maybe up to a ‘medium’) then you would not have any thermal issues to complain about. I guess that be a preferred option?
A small light with a turbo output is fundamentally a short term situation due to thermal limitations. Its physics that cannot be avoided with the current efficiency of emitters/drivers and the size of your torch.
With a XM-L driven to full 3A for example, you have a huge amount of heat bring produced. The primary goal is to keep the LED within operating range. up to 80 degrees? ©
There are 2 ways of doing this.
1) Thermal DISSIPATION - removing the energy to the external environment - I.E. heatsink AREA. A large surface area, and airflow over this area helps to remove this heat energy to the air. You need a large area to effectively keep the LED within operating temperature.
Using this calculator, Assuming a plate area of 50square cm (the surface area of your pocket rocket XM-L torch), and airflow rate of 1m/s (walking around). Lets also name 60 DegC as the hand scorching temperature.
http://www.efunda.com/formulae/heat_transfer/convection_forced/calc_lamflow_isothermalplate.cfm#calc
A 50square cm plate, with 1m/s air flow over the plate, for a plate at 60 Deg C, ambient 25 deg C, is able to dissipate around 3Watts of heat.
If your XM-L is generating 10W of heat on turbo, your LED generates much more heat than 3W, so temperature will continue to rise beyond hand scorching temperatures (about 60 deg?)
Using the calculator again, at around 130 degC, the 50 square cm plate will finally be able to Continuously dissipate your 10 watts of heat. So its therefore quite obvious that your small pocket rocket has no chance of keeping up with a fully driven XM-L from a thermal dissipation point of view without getting to ridiculous temperatures.
If we however increased the plate size to 200 square cm, (10x20cm plate) which is closer to that of a large 3x18650 torch body), it can comfortably dissipate well over 10 watts, and stay below 60 degrees.
SO what else is there for our little pocket rocket….
2) Thermal MASS - the mass of the heatSink absorbs the thermal energy. So the larger the thermal mass, the longer it takes to warm up the torch. (like putting more water in your kettle, means it takes longer to reach boiling point for a given energy input)
Your pocket rocket is a small device again. Lets say it has an effective thermal mass of 50 grams? Lets be generous and say its 100 grams of material that you can heat up (thermal resistance not included). For a 10 watt heat source running for 1 hour, your 100 gram aluminium body will increase in temperature by around 400 degrees C.
Thats a little warm! If we divided that down to 5 minutes, thats a 30 degree rise. So if we start at 25 degrees, we will end up with a 55 degree torch in 5 minutes. Realistically most of the torch doesnt actually get heated up, the battery tube is connected with grease through a thin threaded section, the battery is not really connected thermally to the LED at all, and remember that your driver board also puts out heat too!.
A 500 gram thermal mass however with a 10W heat source for 1 hour will only rise 80 degrees. SO even with NO heat dissipation, by 1 hours time it will only rise 80 degrees. And as we have shown above, with sufficient surface area, it is well and truly able to continuously dissipate heat anyway.
So physics is at play here, there are no 2 ways around pocket rockets and heat. We have demonstrated that its too small to continiously dissipate heat, and too small to absorb the heat without getting crazy hot, and rapidly. The only way is to Reduce the heat being generated (turn the output right down (medium mode?)), or use more efficient emitters (every new emitter released is improving on this), or increasing the rate of cooling (airflow, surface area).
In conclusion, I agree that many compact lights have a turbo mode, and it would be nice to expect to be able to utilise the full runtime quoted on turbo in one hit. A light that is able to deliver turbo continiously is indeed a better light, however you must understand whats happening to allow for reasonable expectations.
With a physically small torch, using current LEDs the manufacturer can offer up to 200 lumens safely, but the consumer wants more, so turbo is offered to you with a caveat of short term operation, which is limited by the physics of thermal management of a static aluminium tube as demonstrated above.
Your hot rod ferrari overheats too, if you dis-respect its operating conditions. If you constantly sit on the red-line and your not moving (airflow for cooling) you can expect it to overheat. A ferrari was designed to race though, so it can rev away if your on the track for hours. Certainly on the limit though.
How about a smaller car, a daily drive, 1.3L 4 cylinder, with the small air intake and small radiator. Designed to run at cruising RPMs, and has a little thermal capacity to handle the occasional hard acceleration. If you were to drive it like you stole it all the time, and sat on the red-line 7000rpm all the way to and from work for a long continuous drive, (and kept it on redline at red lights), you can be sure that its not healthy, and thermally not able to handle this more than a few minutes. If you then went to the manufacturer and complained that the car overheats every day after X minutes of red-lining while parked, Im sure you wont get a happy reply.
My 2 cents, and hour of sitting infront of my computer
Your call. And its fair to choose either.
A) A pocket light that does 60 lumens with 3 modes, 1, 40, 150, can run 150 for all its battery life
B) The same pocket light with 4 modes, 1, 40, 150, 500, with the caveat that the 500 can only run for 5 minutes tops.
C) Or a larger light that keeps reminding you that its in your pocket every time you move, and prevents you from sitting down, that can do 500 lumens continuously.
For EDC, my personal preference is B, because I know that I can use 500 for those 5 seconds I need to check something thats a little further out, or to wow friends when I whip it out of my pocket, and I know I still have my 150 lumen light (option A). (this is of course assuming the UI is not getting in the way, like my V10R for example)
on-line degree in Thermal Dynamics. :bigsmile: Good stuff. Glad you spent the hour in front of the computer for us. Excellent.
However I do have some differing views. I don’t believe that decent engineering design shouldn’t take into consideration human fallibility when it involves things that get hot and can burn to the unsuspecting. Yes, you are no doubt well-versed in the intracacies of using your blazer light in the best and most effective fashion - and you would use it in that fashion. But again, knowing when that light’s 5 minutes is up is one thing. Not knowing if 5 minutes and 36 seconds is just too much is another. Human fallibilities.
Now OTOH, take my techno-naive wife. Please. Ok well, moving on here. If you gave her that same but way too small to be thermally efficient turbo light and instructed her, “Here, take my light. I know it’s feeling real hot to hold honey but shine it on me while I try to extract that little old screaming lady from this smoking wreckage……”, then ya begin to understand what I’m driving at here. The designers of these lights are doing sh*tty slap it together work IMO because brightness sells. Sure. But maybe it’s even unnecessary unsafe work. Maybe housing more of these power lights in inefficient thermal transfering bodies coupled with high-current Li-ons is like sticking hidden nitrous oxide injectors into new cars without telling the owners until they find out whenever the motor goes faster than 5,000 rpm. (This may be a poor analogy. It’s getting late and I pulled this out of my a.)
Now Baterija also writes here excellently, in particular this point IMO,….
“You can also have the light automatically ramp down by time or with a thermal sensor.” I think IMO torches eventually need to go there - especially li-on multi-cells in series. But perhaps I digress.
So how much does it really cost to add such feature-s to a driver? I’m ignorant. And a frissy snoot. What a combo. Quit reminding me. But I’m thinking about the amazing and apparently cheap technology that goes into a $3 digital watch that sets off an alarm 5 days and 22 hours hence, or a $2 calculator that auto-shuts off these days. Does anyone here know?
My point is, if you’re gonna design for example a Mini-01 that blazes and bakes, make it moreso fail-safe. Otherwise what are we turning into here, just dumb light jockeys out for cheap thrills and a little ride with our hot dates? 
Besides I’m actually learning something here, guys. (Now I’m waiting for an Agenthex to chime in. H) )
Internal thermal regulation is the next best thing for that fool-proof light and usually the component cost to incorporate that is at most a couple dollars per unit, if not cents, however its putting it there in the first place that is the problem. And why is that so difficult? It takes a small but decent amount of effort to put this into the design (and a bit of space)… Technicalities aside, it all comes down to price, consumer demand, and overall mindset.
Many of the modern lights that your paying upwards of $50, 100, 300 for, do come with such features, and in some instances even have battery voltage readouts, and even let you choose how the torch brightness goes down as the battery runs flat (fully regulated, to stepped decrease, to smooth gradual decrease). I even own a couple of these, and they even advertise the ability to run full bore till the battery dies in warm climates!
But its all down to cost. If your willing to pay for it, it can be done. Lets go to the other end of the scale where your bargain bin torch produced by a factory (most likely in china) will have some budget emitter, slapped on a standard led board, and if your lucky thats screwed onto a standard aluminium head/body, in goes a driver (floating around), and in goes a battery. Give it lots of amps, out come some lumens, whack on a nice big lumen figure and away we go.
It might not even work half the time after a month of trying it out, and your asking for thermal design Most of these have the classic LED star mounted onto a tube, so the back of the LED isnt even on anything substantial. They feel cold outside because the heat never even gets out to the tube, your just roasting an LED. But you might have only paid $15 for it.
Again, expectations must reflect what your asking for. Impossibly compact, Impossibly bright, with runtime to boot and most importantly, bottom dollar. As many have stated in the past, you can only choose a few of the above, and rarely do you get to play with all of them. Its dependent on where your goal posts are. A couple years back, and we were WOWing at the short of 100 lumens we could get with a maglight 4D LED! (and its thermal design is pretty poor, it already needs to ramp down after a few mins of 100 lumens!)
So if you want it all, paying for it in some way or other helps you to achieve the goals.
Oh and 5 minutes, 5:32.12315… it doesnt matter. Unless you have gear to internally measure temperatures, there is no real limit to time. It depends on everything, External temperature, air velocity, air direction, air density, types of material in contact, how fast the blood is flowing in your hand if holding the torch, what battery your using, the internal resistance of your battery, the position of the moon (affecting the tide, therefore affecting whether your indoors or outdoors catching crabs in the river), the total thermal design mechanically and electrically are most important.
LEDs dont die instantly past a certain temperature, its accumulated reduction in performance. So how you want to use it dictates how long you will get to enjoy higher performance from your torch. No one says you should stop using it after it passes hand searing temperatures. A better design will let you run it longer and brighter, simple as that.
If it doesn't overheat, then there's room for making it brighter 
Toughen up!
Speaking of which and this is a segue to the original thread, when I did a BLF search on ‘thermal sensors’ this is one of the first things it pulled up. I find it interesting that a cheap hobby charger has a thermal sensor to detect when a batt is getting too hot, another sensor for timer cut-off, and finally a capacity cut-off sensor. Don’t know how involved those aspects are but one might think at least a thermal sensor or timer cut-off on a hi-power torch’s driver is attainable for a modder to incorporate (?).
Which brings up another deal. I wish that the Intellicharger i4 had especially the thermal sensor or at least the timer cut-off feature. Prolly the thermal sensor is the cheaper way to go because it’s automatic. If a cheap hobby charger can incorporate it, so could Nitecore IMO. I’d pay an extra buck or two to have at least one of those options built in. And I think going by what the charger below could do it’s not a price consumer issue for the product either. Again, everyone raves about this charger - and I have one, but in retrospect maybe it’s not that great a design considering what other inexpensive chargers can do sensor-wise especially for li-ions where it’s flat-out needed the most.
Man, I’m on a frissy snoot soap box about kinda poopy designs when ya really think about it this morning, ain’t I? :cowboy_hat_face:
Hand warmer on cold winter nights walking the mutt in negative 10 degree weather. That's Celsius for you Fahrenheit guys.
Those slutty mermaids can never be trusted.
imagine what you could catch outta the water.
why not use it as an immersion heater, then?
‘budget’ diving light out there is a royal POS too.
OK, I’m a lone voice who agrees with you. I have no use for (nor have any) flashlights that will self destruct if left on high for too long.
Partly because my light collection started in response to our frequent storm related power outages where lights must be able to run for hours without fail.
Partly because if someone were to borrow one of these many lights for such emergency use, I don’t want any harm to the light or them to result.
Partly because I tend to follow LED manufacturers specs for Max amps and temps the device can endure without failure. For emergency use, I want a light that is unlikely to fail in long term use.
Partly because when it is truly dark and I need the light, it seems that a couple hundred lumen or so is almost always more than enough. More often 20-50 lumen is enough for my use.
Partly because for my use, 4 or 5 (or 8-10…) 100-200 lumen lights is far more useful than one blazing bright short lived hot running 1200 lumen light.
YMMV depending on YOUR requirements.
The only real things I dont like hot is my beer and scotch, pretty much everything else has to be hot. Tried cooking on a cold barby? My wife was once hot and now is a fantastic mum. I was once hot but now am just a fat middle aged man. The sun is pretty hot and its a big flash light of sorts. Back to the subject at hand,
If your light gets too hot what do ya got?.............................................
A really hot flash light and that I like.
…… 8)