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15-year-old girl invents flashlight powered by the heat of your hand (extremetech.com)
386 points by evo_9 1484 days ago | hide | past | web | 121 comments | favorite



Wow, her dad is my coworker and I heard this casually mentioned at work the other day that his daughter was working with Peltiers and I should consult with her because I am also working with Peltiers for characterization of phase change materials.

Also note, calling the device a Peltier is a misnomer, her flashlight is a thermoelectric device utilizing the Seebeck Effect, similar but opposite to the Peltier Effect. Peltier has just become the connotation for thermoelectric devices.

The Seebeck effect only works with a temperature gradient, the flashlight will begin to heat up when held and the Peltier will produce less power. The next step is to add a heat sink and fan to maintain a temperature gradient for operation longer than 20mins.


When I was in high school I looked into making a micro-power plant using the Seebeck effect for the Intel Science Talent Search. I thought about using liquid sodium as a heat sink, which is what some heliostats use. Solar power towers use the captured energy to power turbines, but this isn't very efficient, so I thought I would add thermoelectric generators to capture some of the energy that is lost as heat.

I ended up not doing this because the Seebeck effect isn't really a useful power-plant (in the broad sense of the word) when you have a small temperature gradient because it is really inefficient, although it is useful for thermometers and other low power items, and for some exotic things like Radioisotope Thermoelectric Generators, which is what powers Voyager and other long distance spacecraft. It becomes worth using when you have a large, consistent energy source, which is usually geothermal energy. But the small temperature difference between the human body and the flashlight and the low efficiency of thermocouples means that this project won't seriously compete with battery powered flashlights. However, it is a cool idea and could have some niche uses.


Yup, Seebeck is incredibly inefficient, as for RTG's in space I think they would rather use a Rankine cycle but that would be prohibitively too heavy to launch.

Good on your for using peltiers back in HS. In HS I made a sweet exoskeleton using peltiers for active cooling while outside in the summer heat.


>Seebeck is incredibly inefficient

Yep, I was going to try to use that (peltier) in conjunction with a small array of solar panels to cool my car because summer afternoons can get incredibly hot - outside temperature reaches 45C, so I'm reasonably sure the car's interior would reach 55-60 easy. Alas! running some back of the envelope calculations (before jumping into the whole thing) I quickly discovered that I'm better off trying to find an efficient and tiny compressor, and large secondary battery to charge off the solar panels.

This problem still remains unsolved and no, remote start is not an option. I'm trying to craft something that is completely independent of the gas in the tank and preferably self sufficient.


> Yep, I was going to try to use that (peltier) in conjunction with a small array of solar panels to cool my car because summer afternoons can get incredibly hot

A simple reflective car cover would do far more than all of that tech.

Smetimes it is really easy to over-engineer solutions to problems. I am reminded (and I am guilty) of this frequently.


This $15 thing will help with those first 15 C. Fancier ones exist.

http://www.sportsimportsltd.com/sopoaucofan.html


I got that as a gift, and I have to unfortunately state that it's a negative. It does not help. Actually it helps even worse than cracking the windows down a little.

I do realize that the problem needs to be approached two fold - expelling hot air outside to reach ambient + cooling air that's being taken in some manner.


In full sun a car can easily have 1+kw of heat gain. Combating that with AC takes a lot of energy especially when you consider how long a car may be sitting out in the sun. But, cutting down on heat gain either by parking in the shade or having reflective shades can get you to close to air temperature fairly easily. However, combining would make things a lot easer.

So, if your willing to go all out and spend a few thousand on modding your car. Automatic shades for every window, a fair sized solar array on the roof and an independent AC system designed for continuous operation.


Spacecraft use RTGs for reliability—they have no moving parts. Moving parts kill space missions.


Interestingly there have actually been a few nuclear reactors in space. Used primarily for radar satellites iirc that need power that RTGs and solar panels cannot provide.


Wow, an encouraging comment on HN? Not assuming they're a moron?!?! You give me hope for this place.

Speaking of phase-change materials, why not fill the flashlight with them? It still wouldn't be steady-state of course, but I envision the fan eating up all the power. Heat pipes might help, but they still leave the problem of heat rejection. Evaporative cooling pad?


Thanks, No doubt the fan would eat most of the power, thats just another engineering challenge to overcome. There doesnt seem like a better way without making the flashlight huge, then again the scale of power I am used to is an several orders of magnitude greater than what she uses, I probably have a scale bias. Im sure she could design an innovative passive and small heatsink.

Idea: using PCM you could make a flashlight that you recharge in the oven.


True, or by leaving it in the sun.

Combining ideas may make sense here. A flashlight with PCM and a black handle that you can leave in the sun, and optionally wrap in a soaked cloth. Perhaps PV makes more sense, but I haven't run the math.

Of course, you'd also want a thermos to carry it in. ;)


Paraffin would be a good choice, although just putting a slug of copper into it and storing it in the freezer would probably work just as well. Of course you have to be able to find your freezer in the dark ...


Paraffin would be excellent. In fact, wax + copper was such an excellent combination to pull away thermal energy, this was the same mechanism used on the NASA Lunar Rover :

http://en.wikipedia.org/wiki/Lunar_Roving_Vehicle#Wheels_and...

Basically, the heat was stored in the wax, which melted. Then, radiators would pull the heat from the wax out into space when the Rover was resting, which would solidify the wax again ready for the next run.


Careful now. The space-rover-cooling regime is substantially different from the handheld-Seebeck-flashlight regime. What makes sense in one place doesn't necessarily make sense in the other.

Think of sink/source temperature, cost/mass/performance/reliability tradeoffs, air vs. vacuum, power requirements, etc.


Wouk the wax be in a copper tube, or would you have a copper tube/rod in the center of a pool of wax?

What about a series of smaller copper tubes that then stick out the bottom of the handle to transfer heat from inside to outer air?


That's how coffee joulies work! http://en.wikipedia.org/wiki/Coffee_Joulies


Except that, you know, they don’t actually work. Even the creators admitted to as much.

http://boingboing.net/2011/10/26/coffee-joulies-review-the-e...


T.T But the idea was so neat!


Heck, ice would be pretty good, and would maintain a large ∆T until it melted. Copper's a great conductor, but the specific heat is pretty poor: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/sphtt.html

I guess it also depends on the relative importance of mass vs. volume optimization.


Does paraffin melt at body temperature? Not even core body temperature, hand temperature at a time when the air temperature is substantially lower.

Maybe there's some way to lower the melting point of paraffin?


I also don't quite think incorporating a fan into the design would increase it's efficiency. A quick google trip for PC Fan power usage gives me 1-2 watts for a 80mm fan. Small 5mm LEDs at 20mA and 3V should, calculated via rule of thumb, be at roughly 60 something mW. It just doesn't quite add up.

Evaporative cooling could work, but if you are planning on even including 20ml of cooling liquid, you could just as well put a CR2032 battery in there, which'll power the thing just fine.


Shocked that the top comment is not just another one criticizing or trying to diminish something about the article/story.


Is it accurate to say the device would perform better in cold environments than warm environments, then?


I believe that would be an accurate statement, yes, and it also would seem that the performance of the device would increase non-linearly.


A fan might be counterproductive, drowning too much current.


Greetings fellow Victorian.


Victoria HN meetup? :D


A heat sink yes, but a fan? The electrical output is already very low.


Invented is a strong word when these already exist.

http://www.youtube.com/watch?v=pFqrx2-ENgE


You don't have to be the first one to invent something, to invent it.

It doesn't suddenly become imitation if you came up with it on your own.


Of course, but with nowadays available information and possibilities to search, it is quite easy to find that it is already done. I mean, I don't think she invented it being sitting in some cave, without contact to outside world. She would at least need to have done some simple research, with the materials and etc... So some organic results would pop up.


Interesting. More info here:

http://thermalforce.de/de/product/module/index.php

http://thermalforce.de/de/download/m101.pdf

ThermalForce says price is available upon request -- so it may be available for sale as a custom order. There are some other interesting products at that first link as well.


She is more eloquent and capable of public speaking that a lot of adults.

More women should see example like these, it is a great example of woman in engineering kicking ass.


Very clever!

I'll state for the purposes of prior art that, if you can get enough power to add a little fan or other air-moving mechanism to the circuit to pull air through the tube/heatsink, it will operate in still air for as long as a human can keep it warm.

This opens the mind to a realm of interesting body-powered devices, especially in environments where heat sinking is easy, like for divers, motorcycle riders, and sailors. Want a wetsuit or jacket that lights up or operates sensors on its own? Easy peasy.


Unless you are planning on keeping warm in those environments, which would make strapping heat sinks all over your body a bad idea.


My favourite part of the article was: "The flashlight maintained a sufficient level of light for over 20 minutes, definitely enough time to find the candles in the dark when the power goes out."

Why not just put the candles where the flashlight was in the first place? (or just put a reliable battery powered flashlight there.)

It sounds like it's saying "this flashlight should last long enough for you to find your better flashlight".


Looks like she's just using the Peltier effect to power some LEDs. I doubt the flashlights would work well, if at all, at room temperature but would be useful in a cold climate.


Well the article does say that it works ok at 41 degrees and kinda sorta at 50 degrees. As with most things, its level of impressiveness varies with your understanding of the physics involved.

The interesting question for a science fair would be to see what she had learned of the science. Did she evaluate the efficiency of the Peltier device? (typically single digit percentages) Did she compute the amount of work you could do with different energy differentials? Coming up with the total joules available, versus the joules harvested? Did she look at the efficiency of the LED to convert energy into light. What is its lumens per joule rating, and given the choices did she look at single color light (say red) versus broad spectrum light via a 'white' LED (which is a UV led exciting phosphors to get different colors). Did she go over the various enhancement strategies (drop an ice cube in a hollow tube inside the light?).

And most importantly, given what she has learned about how one can convert a temperature differential into work, what other problems might she solve with that principle?

It is unfortunate that ExtremeTech goes for the link baitey angle "ooh a flashlight that works off body heat" and less on the "Hey if we teach kids real science, they can do stuff!" (which in my opinion is a better angle on the story).


Yes, that's essentially the functionality of the flashlight, which makes it no less remarkable an accomplishment for someone her age.

I don't care about the use case or whether it works well. I care that it exists.


I'm not sure how it works but would having a small recess of water inside the flashlight help maintain the temperature difference? So that when you have used the flashlight enough that its temperature has risen to that of your hand, you can fill it up with water or ice and it'll cool down a little.


> " I doubt the flashlights would work well, if at all, at room temperature"

I found it a bit disappointing that they mentioned one use case as finding candles when the power is out, shortly after mentioning that it works only marginally at 50 degrees F. It takes quite a while for a normally-heated house to drop to that temperature.

It's a neat invention, no doubt, but the practical use cases for this particular version are going to be outdoors.


If the exhaust from a candle (think small, like a tea light) can be made to travel upward through the tube, and the exterior of the flashlight given sufficient heatsinking, it's possible that this arrangement can yield more visible light than the candle can produce.

I'd have to work through numbers to guess, and do the experiment to be sure...


Here's the productized version of that idea: http://www.thepowerpot.com/

The consensus of the camping community seems to be that it's not worth it. Batteries + camping stove is easier/cheaper.


Did you read the comments under the article? I usually do not buy sexism in tech, but this got me.


> Did you read the comments under the article?

It usually isn't a good idea.

> I usually do not buy sexism in tech

So I guess you don't "buy" it because you don't usually see it, if only on account of not being on the receiving end of it?


You have no idea who I am, so please keep your guessing to yourself.


> You have no idea who I am

Well you're the one who just had to note you don't buy sexism in tech.


Who are you?


I came here to see if anyone else noticed the sexists comments under the article, what a shame.

However it's not difficult to find sexists pricks in tech.


>However it's not difficult to find sexists pricks in tech.

Or online, or in public.


You're probably just the only two who read the comments...


I think the comments were removed, but one of them said that she should build a body-powered vibrator and she would be millionaire.


They must have been removed. The 8 comments that are there are quite benign


The fact that gender is mentioned in the headline and discussed there and here points to a different standard for males and females I think. If it was just a passing reference, no problem, but the fact ITS A GIRL is somehow amazing. That's sad.


I totally agree. I think the fact that her gender was brought up so much demeans her accomplishment and insults her a bit. Sadly, we as a culture are still figuring this all out.


Not to complain, but how much light does it really produce ? Cause this would be very neat ... but I still need to be able to light the room :)


From her project description[1]:

My objective in my project was to create a flashlight that runs solely on the heat of the human hand. Using four Peltier tiles and the temperature difference between the palm of the hand and ambient air, I designed a flashlight that provides bright light without batteries or moving parts. My design is ergonomic, thermodynamically efficient, and only needs a five degree temperature difference to work and produce up to 5.4 mW at 5 foot candles of brightness.

5 foot candles is about 54 lux. 30 to 50 lux is minimal illuminance for reading.

[1] http://www.googlesciencefair.com/en/projects/ahJzfnNjaWVuY2V...


Thanks


I guess this is a consequence of the development of the LED. LEDs being so efficient allows for very low power sources and a thermocouple seems to be enough to light them. Pretty cool!


First I have to say that this is very cool indeed!

Practically speaking, however, I'm not sure that it would have any advantages over the flashlights that you crank for a while. Though perhaps those crank flashlights use a rechargeable battery that degrades over time, and this new flashlight would have a longer shelf-life? Though I should think a good capacitor instead of a battery would solve that potential problem with the crank flashlights.


Junk like this:

http://dx.com/c/flashlights-lasers-999/led-flashlights-901/a...

will make quite a lot of light using a single NIMH AA that has been out of a charger for weeks (pushing ~ 1 volt...). It doesn't get you to 0 batteries, but it does a nice job of making light when you happen to realize you need it (without thinking about it in the interim).


I've never had one of those crank flashlights work after more than a few hours of use. I bought several for my kids, and they didn't even make it through a weekend camping trip. I also tried keeping one in my car, and found that the second or third time I tried to use it, it would light up dimly for a few seconds after several minutes of cranking. Some component, either the capacitor or the generator, has a very high failure rate.


Those crank-powered flashlights make a lot of noise and induce cramps in the hand used to crank it.


It seems to work well for me. My son loves his. Granted I don't use it as a necessity.


It's a great idea and a great science project, I just don't see how practical it would be due to how little light it would produce. Even if I kept it in the back of my car to aid in a possible road repair (perfect situation for a no battery device) I don't know how effective it would be. Perhaps that's just the skeptic in me?


Maybe we could just be happy for the kid and imagine what she could be making at 25?


I think a lot of people react to the sensationalism of the headlines on stories like this. It's absolutely wonderful that a 15 year old girl is interested in experimenting with little bits of tech like this, and I'm sure she's way ahead of the curve, but the news outlets like to portray this as "15 year old kid invents a new solution to a difficult problem," which is just way overstating it in the annoying style of people who are overly impressed by their own grandchildren's science projects.

Just from the headline, I said to myself, "sounds like some kid discovered peltier junctions and LEDs and the media decided to act like she's invented something," which was exactly right. Good for her, she's learning and experimenting, and that's a great thing, but let's not get carried away with our portrayal of how amazing it is.

Think back a month or so to the girl who "invented" a new way of charging cellphones in 30 seconds using capacitors. The sensationalism of that story was so over the top, I had non-technical people sharing the story with me on Facebook with breathless comments about what a genius this kid was and looking forward to this fantastic tech being available in all of our cell phones. Was it anything like that? No. It was a kid experimenting with well-understood technology and learning how things work, and there was no discovery or invention of anything non-obvious to any actual engineer. I don't want to detract from her industriousness or enthusiasm for learning, but when half the world is convinced she's done something notable enough to get her on the talk show circuit, something is wrong with the reporting.


So we can probably all: (A) see through the sensationalism and be happy for the youngin' or (B) react to the sensationalism or (C) both.

I'm cool with A or C. B seems lame.


Totally, but if you saw a headline "16 year old invents new communications medium" and it turns out it was a PHP guestbook, and major news outlets were making a huge deal about it, it kinda makes sense that there would be some backlash, even though a kid learning to code is, IEHO, pretty fucking cool.


Why focus only on the negative, or on a situation for which it would obviously be a terrible choice? It's never going to be as powerful as a battery powered flashlight; that's not really the point.

It might, however, be awfully useful in a stiatuion where there is no ambient light available at all, or where equipment needs to be light and very simply constructed. Perhaps something like in an emergency kit in case of a mine or cave collapse. Or in a situation with very adverse operating conditions, like a desert. Moving parts (as for a hand crank torch) would be a liability in an environment with omnipresent particulate contamination.


And this is why people get cranky at articles like this, people are not adult enough to take them as what they are, puff pieces to build the esteem of children.

Could a 15 year old child invent safety equipment for the trillion $ mining corps. Of course not.

People with 4 year degrees in engineering have as much commitment and inventiveness as children and money to boot. Plus a fully developed brain.

As is always the case child age x invents new way to do blah, invents object blah they of course haven't.

As a tired cliche does it have a place on HN. Is this site aimed in part at children is the question?


I don't know about mining, but I do know that some pretty damn simple things make a hell of a difference. Hospital safety has been improved quite impressively (or disturbingly, depending on your perspective) by using a checklist prior to surgery. Questions identifying the surgical site feature on the list, and writing on the site too. Staff are asked if anyone has any concerns. It's amazing what a group of highly trained individuals can screw up without child-like safety systems being in place. http://www.npsa.nhs.uk/corporate/news/surgical-safety-checkl...


This stuff is really interesting but is a million miles away from child-like.

We've know for years washing your hands in hospitals saves lives.

And we've know for years people are not doing it. Even just putting up signs helps an amazing amount, but even this isn't done.

Cause it's a really hard problem.

How does one improve the issue? Some hospitals are trying cameras, ranking deaths in hospitals, rfid tags tracking people making sure they wash.

I'm willing to bet even though the checklist above is pretty close to proven most hospitals don't use it.

[edit] http://online.wsj.com/article/SB1000087239639044462010457800...


Good point - its the problem that's simple and while the solution appears simple too, getting someone to cut into the correct side isn't easy.


You'd better hope ambient temperature is less than 50 degrees.


What is the hypothesis? As a science fair project, while this is novel as far as most "I made a volcano using baking soda and vinegar" projects are, I'm missing the scientific method in what I've read so far.


Hypothesis: The Seebeck effect, combined with the heat from a human hand, can generate sufficient power for an LED flashlight at room temperature.

The hypothesis was approached from both the theoretical and experimental side.


This flashlight wouldn't be great for lighting up shadows created by strong ambient light, but in complete darkness, even a little light makes a huge difference.

I'm thinking backup light source for camping, spelunking, power outages at home... just enough light to find a path when there is no other light.


Put this in phones to charge them when you aren't using it?


Won't work very long, it operates using the temperature differential between your hand and the interior of the flashlight. Which, based on the quoted "still worked at 50 degrees F", means you'd have to stick your phone in the fridge when you're not using it. And then take it out so it can charge just a little bit before the temperature equalizes.


Alternative, could you use this to capture waste heat from the phone internals?


Blean (n.)

Scientific measure of luminosity : 1 glimmer = 100,000 bleans. Usherettes' torches are designed to produce between 2.5 and 4 bleans, enabling them to assist you in falling downstairs, treading on people or putting your hand into a Neapolitan tub when reaching for change.

~ Douglas Adams and John Lloyd


Can this technology work in an airconditioned room? I was thinking if this technology can provide enough electricity to even just lighting up a single room. It can use the heat outside, and the cool air (form air condition) inside the room.

All in all, very good invention! And also inspiring. I hope more teens will be involve in inventing things. I hope she wins. Also, (totally unrelated) I think she's cute. :)


It should be provable that thermodynamics guarantees that it will be more power-efficient to generate the light directly with electricity instead of using electricity to cool the room, then exploiting a thermal gradient with even a lossless Peltier element.


True, and it is. However, if you are going to be using that energy to cool the room anyway, why not try to reclaim that 'spent' energy?


If you wish to have

1) a cool room at temperature T

2) enough light, L, to see by

3) a happy human at temperature H

Assuming that T,H, and L are fixed, you're going to use more energy with a less-efficient process. So, you'll 'spend' more energy to get there.

If you're trying to run the process at fixed energy, you're going to wind up accepting a slightly higher T. If that's the case, you'd be able to use even less energy by powering the LED directly and moving the setpoint for T up to that same temperature.


I think what you are forgetting is that in doing so, you would be heating the room up again.

So to keep the temperature where you want it, you'd need to cool the room even more.


Ahh, you are right.


TFA:

due to the temperature reliance of Peltier tiles, the flashlights worked better in colder temperatures (tested at 41 degrees Fahrenheit). The flashlight still worked in warmer temperatures (50 degrees, for instance), but the colder the surrounding temperature, the more the hand’s body heat can help the Peltier generate electricity.


It would 'work' but it would be grossly inefficient. Your room is cooled by a heat pump(air conditioner) a Peltier is just a different heat pump, a very inefficient one at that. You would end up spending much more money cooling the room than it would cost to just power lights normally.


Sorry, what you're talking about is a perpetual motion machine, which the laws of thermodynamics forbid. The AC will just have to work harder to get the extra heat added by the thermoelectric device back out, no free energy here.


Thanks. Never had a knowledge about thermodynamics. I just googled perpetual motion and the laws of thermodynamics. And yes, I agree that my comment above doesn't follow those laws. It's good to learn these new things. :-)


No problem, keep on learning! :-)


I can't help thinking of a full body suit to harvest the entire heat output of the human body. Maybe you could use assisted sweat evaporation to provide for the cold tile?

It could be like a Fremen suit so they can pump the water coolant around and potentially and power electronics.


I'm pretty sure the result of that would be that you would overheat as the suit would prevent you from dissipating heat quickly enough.


I think the risk is that you'd have the opposite problem: hypothermia.


I'm a little shaky on the thermodynamics of peltiers, but it seems (and I swear I read something years ago to back this up) that if it extracts power from the equalization of a heat differential, it must also slow down the conduction of heat. Two arguments for why this should be the case:

1. If it were not the case, then assuming ideal peltiers, you should be able to simply stack one peltier after another and get more energy than just one from the same temperature differential. And that's clearly crazy talk. If peltiers do not impede heat conduction, they must have some other limitation that prevents this from being the case.

2. Peltiers are reversible; a thermoelectric generator also acts as a thermoelectric cooler if you put current through it. So when you heat one side of the peltier and cool the other, generating a current, then that current should cause it to simultaneously act as a TEC (analogously to how counter-EMF causes an electromagnetic generator to resist as you turn it, essentially by turning it into a motor trying to turn in the opposite direction). That is, the very current you are generating will cause the peltier to transfer heat from the cold side to the hot side, with the end result that it would act as an insulator.

Edit: However, if I'm right about this, then assuming you can have efficient and flexible peltiers, it should work quite well for winter clothing.


I realized, thinking about this more, that my reasoning must be backwards on point number 2. If it worked as I said, then putting a current through a peltier would actually cause positive feedback resulting in a perpetual heat pump, which is clearly impossible.

So the current running through a peltier acting as a generator should actually transfer heat from the cold side to the hot side, making it act as a better conductor of heat. I don't know how to reconcile this with argument 1, but as far as my knowledge of thermodynamics is concerned, 2 has to trump 1.

So I figure I must be wrong, and peltier generators must conduct heat quite well. In which case I guess it would be good for summer wear - but then, in the summer, the differential between the human body and the surrounding air isn't all that great.


Yeah I was thinking of the approach used in the invention described in the OP, with a pre-chilled slug used to set up a temporary gradient. In that case you could lose too much body heat to warming up the cold mass.

But even without pre-chilling (i.e. in the steady-state case), while you may be right that a TE device necessarily slows down the conduction of heat across a gradient, I don't think it follows that any such 'suit' would result in overheating rather than hypothermia.

Consider 2 people in a 70-degree (F) room. One wearing light clothing, and the other sitting in a tub of water. The water in the tub will equilibrate at somewhere warmer than 70 degrees, and the person will become hypothermic, since the capacity of their 'suit' to conduct heat to the environment is greater than the ability of their body to generate heat to compensate. You could have a TE device that extracted power from the gradient between the warm water and the room without saving the person from hypothermia.

That is to say, I think we're both wrong :): a well-designed suit could keep the amount of heat transferred within the range of the needs and capabilities of the human body.

(Fun trivia: according to Murray Hamlet, a US Army cold weather injury researcher, the leading cause of 'morgue wakeups' in the US is drug users who pass out in the bath, become severely hypothermic, and are wrongly declared dead).


As someone with poor circulaton to the extremities I fear I would be walking around in the dark holding the flash light with cold hands.

Its a really nice idea though. Its stories like this that make me wish i paid a bit more attention in science when i was younger.


If your extremities' temperature is cooler than the ambient temperature, maybe all you need is a version with the heat-collection plates flipped?


If your extremities' temperature is cooler than the ambient temperature, how did you do that? Heat pumps in your arms? ;)

It would be trivial to put some circuitry in there to rectify the voltage so it works in either direction. No separate version required.

(changing ambient temperature is the obvious answer to my joke, btw)


Although others that have responded to this thread have far more experience, I believe Peltiers are optimized to work in one direction. That is to say there is a hot and cold side, so I'm not sure it is as simple as adding an inverter. Not that you'd likely be using your hands as a heat sync anyway.

Yes, I realize this was meant as a joke, but I'm still curious if current can be reversed by just changing the gradient. Does it still work but maybe it is less efficient? Is there no difference at all?


Ah, good point. I hadn't considered that. It looks like you are correct! You might sandwich two Seebeck-Peltier devices and switch between them, though.

https://en.wikipedia.org/wiki/Thermoelectric_effect


She should be using blue LEDs. I swear those things can send light through a wall.


I bought a pack of 400 little round black stickers only for the purpose of covering blue leds... For most of the devices I have with blue leds it takes 2-3 stickers on top of each others to dim them enough for me to still see them but not feel blinded when the light in the room is dimmed..


They certainly are bright, but the light is a terrible colour for us humans. An Optician friend explained to me that the shorter wavelength of blue light causes it to focus in front of the retina, which is why blue LEDs appear out of focus when you look at them.


Way to go. Good to see a girl that age interested in science and engineering.


Reminded me of the Seiko Thermic, a wristwatch powered on the same principle.


For anyone interested, here's the list of all the finalists this year - most of them much more impressive.

http://www.businessinsider.com/2013-google-science-fair-fina...


There is an old Chinese saying: I wish she was my daughter.


Just out of curiosity, what's the Chinese expression? Is it a 成語?


Sounds similar to the fiber optic cable material found @ Roswell, NM. 1947...


Except the flashlight actually exists.


She should call it the Fleshlight


Google 'fleshlight' and I'm sure you'll agree it would be a pretty bad choice of name.


whoosh


It says that in the comments below the article.


So if she is using the power of the human body to power a flashlight when she is 15, does that mean she'll design the technical foundation of the Matrix when she is 30? (which had the purpose to harvest the human energy)

Sorry, could not resist. Great to see our youth being creative.




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