clear led's are the only ones that change color because they don't have to go through a filter of colored plastic. The colored plastic ones change color in the diode but change back when they go through the colored plastic.
Actually, no. LEDs are pretty monochromatic (except “white” LEDs which use a phosphor to convert blue to white), and the colored plastic acts as a filter, which doesn’t change the wavelengths emitted, it just attenuates some of them. So it would just look less bright. Try it: run too much current through an LED, but not enough to burn it, and you’ll see it changing color (I heard green ones work well).
Safety Note: Wrap your glass dewar with cloth medical tape so when (not if) it implodes you will only be showered with liquid nitrogen not glass shards. Cheers, Mark ******************************
+tesla500 Well, yes and no. Probably not spontaneously, but if you bang into it with the supply dewar when filling, or when you loss hold of your test piece and drop it through the bottom, or if you knock it over. I have had a few dewars inexplicably implode while filling and my guess is some type of flaw was present possibly just a scratch. We also either plastic coated or caged glass vacuum vessels larger than about half a liter. Cheers, Mark *******************************
Are you talking about having a closed loop LN2 cooling system? No point, water has a higher specific heat capacity and batteries don't work at those temperatures because chemistry basically stops happening.
I did this same experiment a few years ago. When we dipped the LED into the liquid nitrogen, we increased the current through the LED, I can't remember the exact amperage figure but when it got to a few amps it suddenly transitioned to much brighter. My co-worker who arranged this experiment had read that after this transition the LED light becomes coherent (ie: laser light). We were using regular colour LEDs, not the white ones with the phosphor coating.
When my father was a boy "1955ish". A man came to their small country school and did a science show for the kids. He cut a strip of rubber from an inner tube froze it in liquid nitrogen and drove it into a board with a hammer. The hammer head was made from Mercury. He had a small hammer head mold that the hammer handle fit into, he then poured the mercury and dunked the whole thing into the nitrogen. So yeah. Can you pound a rubber nail into a board with a Mercury hammer? I've heard this story many times since I was a boy. I hope to see it some day.
In Liquid Nitrogen, you could overvolt the LEDs. I remember connecting those 3V 1970's leds to 9V, and for a while they would work in cool water. But in nitrogen, they should work a lot longer, and a lot brighter.
Wouldn't the change in the brightness of the LED diode be controlled by the how the light is reflecting through the AQ Ni. ? and the flask it's self is very reflective?
sometimes you can 'repair' broken rows by gently applying force along the row with a tine screwdriver. I had a 100W LED that had some bad rows and it did the trick
Cool video..I work with N2 everyday and yes you can get about 7 months out of that tank as long as you don't set it on concrete..also instead of the metal thermos you may have better luck with a styrofoam ice chest that's what most of the ranchers use when they poor there n2 out of the tanks to work with embryos and what not...it will hold the nitrogen longer than the thermos..again very cool
Hi, it's possible that you did not see a change in color in the LEDs because most of the color is guaranteed by the plastic body of the LED. Try dipping some clear body LEDs. Also, do this ONLY in a very well ventilated room - a small volume of liquid nitrogen can displace vast quantities of air and you get oxygen displacement, which is nasty.
Led's are basically a short circuit, by cooling them down you mess up the circuit that goes with them, (by affecting its resistance) the circuit normally prevents the Led from drawing in infinite amount of current, probably why the 100W led started drawing a high voltage level.
You might mention this somewhere in the video, but the LED brightness might be fooling you. I understand that supercooling can lower resistance, but when you put the led in the base of the flask, you're half-building a flashlight.
The LEDs get brighter due to the lower resistance allowing more power to be pushed through. It's not that they change color, necessarily, it's more that they emit more of the original color/light being produced and brings the light out of balance with the specs of the LED (hence the white light turns blue, according to your explanation of blue LED covered by a yellow phosphor coating making white). I don't think red, green, or blue would change color, just get brighter. Good experiment though! I enjoyed watching.
jeezus ... that high frame-rate is really trippy o.o Also I think the reason the more modern ones get brighter is because of thermal efficiency equaling to less resistance.
i would love to see High-temperature superconductivity experiments ^^ Maybe too expensive and/or hard to get or noise performance experiments with CCD and CMOS sensors
As a matter of interest, what was your thinking behind this video? -did I miss any tricked videos where this colour changing effect was supposedly demonstrated for the non-white LEDs? I mean the colour of emitted light in those cases is tied to the very nature of the doping element involved and temperature, as far as I'm aware, doesn't change the absolute level of excitation which needs to be overcome for them to emit a photon of a particular colour, hence only the brightness is affected by temperature. QED. It's only when you bring a secundary effect into the mix, i.e. the phosphorous translating blue light into white light, a second, temperature dependant (things need to vibratre at a certain amplitude to excite the main, light emitting, material) phenomenon manifests itself. Not wanting to critisize as such, but this result was to be expected. It's cool and all, but: why?
Here's a video where they put an orange LED in liquid nitrogen causing it to turn green: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-4w1HifFayNU.html
Mmmyeah, and the 1st 5 comments on that video are from people saying they can't reproduce the effect. I don't know whether they're using a bi-colour led (which glows orange when both substrates are driven) and the cold shifts the output such the green can overpower the red, or somesuch, but the phyisics behind this is the electrons in the dopant can be in a finite number of states and the fact of exciting them to the higher ones and having them drop back down emits a photon of a certain wavelenght. This takes a finite amount of extra energy and is thus, in theory, independant of temperature other than it will happen more at lower temperature as there's less "noise" due to temperature.and overal conductivity is increased. I might be missing something, but unless there's a video explaining the phenomenon instead of merely showing it, I'm going to err on the side of the colour change being a trick.
I think the problem was that you didn't use clear LEDs. There are clear LEDs which have different colours but a clear type of glass around. The ones I found in a quick search were called "waterclear" or "transparent". Buy a few of them on ebay and I am sure they will work.
It does work, you just need the right type of semiconductor, and it also works with lasers! Watch this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5PquJdIK_z8.html.
LEDs are made from semiconductor .the semiconductor has negative temperature coefficient.So as temperature decreases the resistance increases(opposite to conductors).. and as resistance increases the voltage drop across it increases and thus it has gone brighter..
+GreenAppelPie an infrared LED might be cool to watch, because it might raise higher up into the red spectrum. However, an ultraviolet LED would be fairly boring, as we cannot see ultraviolet with our eyes (neither can *most* cameras) and the wavelength of the UV would just go farther into the UV spectrum. Near UV would be interesting though.
+Brandon Fowlkes I didn't assume anything would be directly visible, I'd just be interested in any current or voltage changes for the different wavelengths.
i have not read all the comments...but in case any one is wondering why the leds got bright and volts went up when they were in the nitrogen...as conductors cool down..their resistance decreases.
Actually, I believe the low temperature increases the semiconductor's energy gap. In other words you need more voltage - with a constant current - that is more energy, to overcome the potential barrier and let electrons combine with electron holes, and therefore to stimulate the emission of photons.
+sc0tte1 The container doesn't have a "cap" per say, it's more like a piece of Styrofoam that sits on top to provide more thermal insulation. This allows the expanding gas to escape, otherwise there would be pressure inside of the container that would need to be vented every time you opened it anyways, which defeats the purpose of even sealing it. The reason that liquid nitrogen does this, is that at room temperature, nitrogen is a gas. Nitrogen has to be cooled down in order to become a liquid. When the liquid nitrogen warms up, it boils just as water would.
+verdatum I got mine used from ebay. I researched many common dewars found on ebay and this one seemed the best of what was available at the time, it has a very long holding time. There are many new dewars that seem reasonably priced from China, but I'm not sure how good those are. There are a lot of Union Carbide/Linde dewars available used relatively cheaply, but there's very little info on them. I was able to dig up a site that said they only have a 30-40 day holding time, so those are out of the question unless you use LN2 quite quickly. If you're searching, try other terms like "Nitrogen Tank" or "Semen Tank", these are often used for transporting semen for artificial insemination of farm animals. Other than that, probably go for something not too old as the vacuum will leak out (in? which way does vacuum leak?) over time and the holding time will get worse.
tesla500 Thanks for the detailed response! Yeah, the, uh, specimen, tanks seem to be one of the more common things to come up on ebay. I've mostly just been looking for one that is a reasonable volume, doesn't look too weatherbeaten, isn't ridiculously priced, and I've got the discretionary income lying around. Those just haven't synced up for me yet; but it's been an on and off search.
From LED datasheets, heat tends to decrease the brightness of yellow LEDs the most. If the junction temperature is very high, its lumens can decrease to 10%. You would need light measurements to find out if the luminous efficacy increases with liquid N2.
When the LED gets brighter is it actually getting more efficient or is the current increasing? (i.e. did you use a current-limited PSU or a series resistor)
+Dr Tune I presume its because its getting colder,lowering the resistance, meaning it can operate more efficiently and give out a brighter light. That would seem logical.
+Dr Tune After Your absolutely right, we can't come to provable findings until we know if the PS increased the voltage or if the Voltage drop across the LED dropped. Please repeat this experiment.
That's not a terrible price... I'll have to look into a dour jar. I have a few experiments I'd like to try out. LN can be used to make some amazing ice cream. :)
how much does LN cost per liter and where does one find it? being able to replace just the glass on an lcd/oled panel is a money maker but the newer panels and esp curved panels are a bitch. great thing is they embrittle with around the min temp of dry ice. ive tried dry ice but it wasnt ideal and i dont want to spend the 10k companies in china want for a ln circulating cold machine. hoping 300 bucks can get me a filled 3l tank of ln
Nitrogen in sealed containers high speed camera action. More semiconductor behavior at low temperatures(overclocking as others have said), superconductivity, any other weird interesting physics affects that can be achieved at those temperatures.
You should try SMD LEDs in my experience they work quite good for showing it. Somethings else to mention, at low temperature u get an increase of the band Gap so the wave length gets lower. But if u try out a green one in it gets orange, that would be the wrong way around. The explanation it a bit complicated but if u are interested i can try to explain it. Just try some SMD LEDs if u have different types, lasers could be also interesting, but don't put something in N2 u don't mind destroying. Have fun, u properly will have
Chill some steel bearing races and drop them to see if they shatter, or use some cast iron, which should be very brittle in lH2. Aluminium rod should also just snap like a straw, depending on the alloy used.
How about dropping in some disposable lighters? Of course, in a safe environment. There are also a number of foods that can be quick frozen and are completely safe to eat immediately afterwards. I'll leave the selection to you. New subscriber here. :-)
Correct-ish, the conductivity increases as the temperature drops as there is less resistance. It didn't change color though because the LEDs weren't actually orange/red just the plastic casing around them were.
Ah and how about seeing if you can turbocharge a peltier element. See how much power you can generate by, for example, having a power resistor heating up one side and having the heat sink on the other side dipped into the nitrogen.
What about an induction. I could imagen the PF getting really bad (which should indicate there are fewer losses) on a unloaded motor nearing fully reactive operation. (if the bearings don't start to bind up)
