Most efficient hand warmer light? (Seriously)

[OnlyownEnergizer250lumen]

What materials/LED/components would make the most efficient hand warmer of a flashlight? I know they sell hand warmers, but I want a flashlight to accomplish this purpose around the house and in the winter. It's the only element that my relatives appreciate about my lights. When they say they are cold, I turbo blast a flashlight into a safe direction for 30s, unscrew tail cap, and hand it to them. They smile for about 5 minutes… then they are cold again and I have to repeat the process.

I want a flashlight that gets hot fast and stays hot long, that uses the least amount of battery drain for the greatest production and retention of heat. The heat should be dispersed as equally across the body of the light as possible, not just a burning hot head with a cold body. Lockout mode would be cool, but not necessary.

Questions:
1. What material and why? (Copper, aluminum, titanium, something else?)
2. What size is most efficient? (Compact 18650 with small exterior surface area? Larger pop-can/2 handed light?)
3. Which battery type has the best efficiency/capacity but can also hit max turbo output to heat body faster? (18650? 21700, 26650?)
4. Thick walled or thin walled flashlight chassis?
5. What VN lights do you recommend to accomplish this niche purpose?

I want to charge the light as rarely as possible and get the most hand-warm-uses per charge. I prefer the light to be pocket friendly for travel/EDC use.

Discuss!

 

[Skylumen]

What materials/LED/components would make the most efficient hand warmer of a flashlight? I know they sell hand warmers, but I want a flashlight to accomplish this purpose around the house and in the winter. It's the only element that my relatives appreciate about my lights. When they say they are cold, I turbo blast a flashlight into a safe direction for 30s, unscrew tail cap, and hand it to them. They smile for about 5 minutes… then they are cold again and I have to repeat the process.

I want a flashlight that gets hot fast and stays hot long, that uses the least amount of battery drain for the greatest production and retention of heat. The heat should be dispersed as equally across the body of the light as possible, not just a burning hot head with a cold body. Lockout mode would be cool, but not necessary.

Questions:
1. What material and why? (Copper, aluminum, titanium, something else?) Copper has a high heat reservoir so it stay warm even after light is turns off. Its weight will also naturally makes you grip it harder. Al is of course good for its weight and fast heat up but also fast cool down. Ti is terrible as the heat generated will be bad for the electronics and also TI doesn't spread heat well so only specific areas will be hot.

2. What size is most efficient? (Compact 18650 with small exterior surface area? Larger pop-can/2 handed light?) Smaller light heats up faster. multi emitter light can also heat up via radiation and not just conduction.

3. Which battery type has the best efficiency/capacity but can also hit max turbo output to heat body faster? (18650? 21700, 26650?) 21700 is likely gives highest cap to volume size.

4. Thick walled or thin walled flashlight chassis? Thin heat up faster and cool down faster. Thick is the opposite.
5. What VN lights do you recommend to accomplish this niche purpose? FW3Cvn or FW3Avn. Compact. Not too heavy for size even in copper. High specific heat allows for fast warm up and long hold of heat even after light is turned off. I would get rid of the clip for a more comfortable hold. Upon start up you get warm radiant heat right away via the LEDs. Multi emitters = improved efficiency at lower levels.

I want to charge the light as rarely as possible and get the most hand-warm-uses per charge. I prefer the light to be pocket friendly for travel/EDC use. XXI triple will give more runtime but this host doesn't heat sink as well and thus slower conductive heat.

Discuss!

 

[OnlyownEnergizer250lumen]

Hmm, great thoughts to consider thank you Vinh!

I just remembered that copper incites a strong odor on the hands… I don't think my family will want to hold the light in bed and on the sofa or while eating food if it does this… so it would really need a permanent thick polish layer which would probably reduce heat transmissibility to the hands?

I think I will side with aluminum. However I am surprised that multi-emitter would generate more heat than an SBT90 considering how hot those get lol.

Now I'm also thinking the body should be as flat and smooth as possible as it will limit surface area and heat should travel more quickly and evenly.

 

[twistedraven]

The hotter the light gets the less efficient it is. Heat is simply the wasted power that isn't converted into light. I've never seen lights got hotter as quickly as ones with SBT90.2 while on turbo.

 

[OnlyownEnergizer250lumen]

The hotter the light gets the less efficient it is. Heat is simply the wasted power that isn't converted into light. I've never seen lights got hotter as quickly as ones with SBT90.2 while on turbo.

Thats an interesting principle to view it from.

So I should buy the smallest/smoothest aluminum light with SBT90.2 with the least amount of heatsink so that the heat goes straight to the body?

Sort of confused now with the differing LED opinions.

 

[twistedraven]

Yeah if you want a light that's going to start frying your hands as soon as possible, get a tiny copper light with an SBT90.2. The light will be forced to step down sooner than later though, because your hands won't be able to sink all that heat from the light.

For sustained heat, you want a light that straddles the line between too much heat before it steps down, and staying really warm. From my experience with the Manker MK37 on its ~1200 lumen mode, the light can run continuously for at least 20 minutes, and the host stays very warm. I'm sure there are other small to popcan sized lights that have a particular mode spacing that allow for just enough thermal dissipation so that it stays real warm but never steps down.

 

[OnlyownEnergizer250lumen]

For sustained heat, you want a light that straddles the line between too much heat before it steps down, and staying really warm. From my experience with the Manker MK37 on its ~1200 lumen mode, the light can run continuously for at least 20 minutes, and the host stays very warm. I'm sure there are other small to popcan sized lights that have a particular mode spacing that allow for just enough thermal dissipation so that it stays real warm but never steps down.

Please note that I don't intend on leaving the light on. Basically imagine someone laying under a blanket freezing cold and they want something to hold onto under a blanket. I don't want the light turning back on once I give it to them-thats a fire hazard!

Its just a temporary hand warmer to help a person warm up... same thing with winter EDC, turn it on facing at the ground for 20 seconds, light gets hot, turn off/unscrew tail/lockout and hold it inside the pocket as a hand warmer.

 

[Thetasigma]

A Zippo handwarmer, produces almost no light, but makes a toasty puck of heat for a good 8 hours when full.

Using a flashlight as a hand warmer is extremely inefficient and akin to mixing your cake mix by driving down a bumpy road instead of using a spoon or a mixer.

 

[OnlyownEnergizer250lumen]

A Zippo handwarmer, produces almost no light, but makes a toasty puck of heat for a good 8 hours when full.

Using a flashlight as a hand warmer is extremely inefficient and akin to mixing your cake mix by driving down a bumpy road instead of using a spoon or a mixer.

That was the most hilarious and accurate illustration I've heard in weeks bwahahahahha. Totally going to suggest that to my family next time we bake.

Problem with the Zippo hand warmer is that now you have two things to carry, and the hand warmer isn't needed frequently. I think I can get 8 hours of heat from an 18650 or 21700 in a flashlight as well. If high/turbo has a 1 hour run time and I'm turning it on for only 20-30 seconds max to keep a hand warm for 3-5 minutes, that should be 6-10 hours of heat. Of course not as consistent temperature as a hand warmer, but that's not the point. Just don't want to carry multiple items, and it's really just an excuse to buy a unique flashlight to say it has its purpose and that its the most appropriate build for the secondary role of warmth.

Additionally, I want to be able to safely fall asleep in bed and prevent fire hazards, so that's why I want a flashlight with lockout mode or unscrew the tail cap... but a true hand warmer is not safe to fall asleep with, because of potential burns or malfunctions.

 

[kerneldrop]

This just proves that one person's trash is another person's treasure

 

[Siriuslite]

The do sell battery powered hand warmers as well

https://www.leevalley.com/en-ca/shop/home/outdoor-recreation/76088-rechargeable-handwarmer?item=45K4219

 

[kerneldrop]

We use a Mr. Heater Buddy in the deer stands.
I remember as an older kid using the Zippo hand warmer in the stands.
When I was a younger kid we only had an open flame propane heater.
Fun times

I know neither are solutions you're looking for.

 

[OnlyownEnergizer250lumen]

To be more specific, I carry a flashlight every day no matter what. 95% of the time I am wearing formal suit pants with very little pocket space. I definitely won't buy a designated hand warmer, but if I can choose to carry a specific flashlight on a cold day, then its a good dual purpose item for me.

I know there are hand warmers that have built in junky flashlights as well, not looking for that.

I am searching for a legit VN light with some WOW-factor, just trying to find one that heats up fast and stays hot long, with an efficient build to transfer heat into the hands, whether inside under the blankets or outside in my suit pants in the winter. Please try to stay on topic by answering the 5 questions outlined in the OP. (I'm not mad! Thank you for all your lovely input so far!)

Currently it looks like a highly compact/smooth bodied (no fins) 21700 Aluminum light (copper is smelly unless you know a good permanent solution to prevent copper smells) with either SBT90.2 or multi-emitters with easy access lockout mode.

Skylumen XXI? Only problem is the extra copper internal heatsink that I would imagine would slow the rate of heat build up/transfer to body requiring additional turn-on time to warm the light body.

 

[kerneldrop]

Sounds like a perfect reason to wear a custom kydex holster to carry your light since your suit pants have smaller pockets.

Business in the front, tactical in the back

 

[OnlyownEnergizer250lumen]

Would unibody construction greatly impact the light's heat distribution across the body?

 

[KITROBASKIN]

This is an interesting design consideration, and a worthy objective, one opinion. It's ok for some people to 'not get it'. I experimented with a cheapo add-on automobile defroster connected to a golf cart sized battery to get some warmth when cleaning up in the morning. (The 800 watt setting sagged the battery quickly and did not give that much heat. The 400 watt setting was paltry. About $35 spent on that less than successful endeavor)

Aluminum transfers heat pretty quickly (though silver and gold are faster) but it seems some mass is in order to prolong the heat output to the hand(s). Unless the metal mass where the LED attaches is really large, it should not take long to start heating the surface of the torch. Then it might be an issue of how much weight you are willing to carry on your person. If you anticipate short term uses, then a single 18650 should suffice. However if you are talking about prolonged warming capability numerous times, then a larger battery/more batteries would be in order.

I would definitely go with a serious copper pill/heatsink in a short body that hands can surround. Years ago I purchased 2 direct drive P60 dropins from Vinh. They might have been dedomed XML2 that got hot really fast. In fact I used them to test different high current batteries; measuring the time it took to get the surface at the head a certain temperature. Had to wait a long time to get the inner part of the flashlight down to base temp again, noting ambient change. The brass pill was not ideal though. I was careful not to run more than a few minutes even in the bitter cold of winter night.

Now a question is what kind of beam cast do you want; floody or more general purpose? An SBT90.2 with a reflector sure sounds fun, but maybe multi emitters will be more useful to you. If you choose direct drive, be sure to not leave it on for too long. Multiple emitters are in concept more efficient and less heat producing, but if you can keep the electrical path super quick with an aggressive power source...

Seems like any of those options would start heating hands with initial activation, shining light on bare hands.

 

[kerneldrop]

Now I do have a TK17vn that heats up quickly on wide-open full-throttle.
It has the Triple W2.1 with custom throw optics.
It's pricey, but that thing is a torch that quickly turns into a hot potato.
And like @KITROBASKIN alluded to, it's really small (18350 light) and the whole thing heats up.
I really really like that light. It's a pocket powerhouse.

 

[OnlyownEnergizer250lumen]

I've always heavily shied away from 18350 cells aside from the GoliathVN which I only let my guard down because of the throw to size ratio and it was W1 so less concern about battery drainage since it was putting out low lumens.

So as far as short bodies go, it would have to be something at least the length of 18650. I'll definitely keep length dimensions in mind though regarding larger cell lights.