How can I make something glow in the infrared -- no flame or AC power?
October 3, 2014 7:59 AM   Subscribe

For a science demonstration at my son's school, I have modified a webcam so it can detect infrared light. I would like to be able to heat up an object (I don't mind what) so that it can be seen on the infrared camera. So far, I have found that I can see a match (even after it has gone out), an IR remote control, and a gas flame. But these are all a bit tricky in the school environment. Ideally, I would have a battery powered device that would heat up a piece of metal enough that it will glow (in the IR) without anyone being able to burn themselves or set light to anything. I don't mind making the device, modifying something, or just buying something.
posted by beniamino to Science & Nature (21 answers total)
Incandescent light bulbs can burn pretty hot (The Easy-Bake Oven ran on one) - have you tried a standard desk lamp that was left on for an hour, then turned off? If it has to be battery-powered, something like the Itty Bitty Book Light might work.
posted by Mchelly at 8:02 AM on October 3, 2014

I'd suggest a couple of those handwarmers that have the little metal clicker in a supersaturated solution of sodium acetate. Widely available, and get nice and warm without anything dangerous going on.
posted by pipeski at 8:03 AM on October 3, 2014 [9 favorites]

You could run some current from a battery through some resistors or even some types of wire depending on how sensitive your camera is to IR.
posted by advicepig at 8:04 AM on October 3, 2014

How about chemical powered? Something like this would work: pocket warmers
posted by Cat Pie Hurts at 8:05 AM on October 3, 2014 [1 favorite]

Just connecting the two terminals of a battery with a length of steel wire might do the trick.
posted by Makwa at 8:05 AM on October 3, 2014

What is the problem with the TV remote?

How about Infrared Illuminators?
posted by kiltedtaco at 8:05 AM on October 3, 2014 [4 favorites]

Bring a thermos of hot water, and a small pair of tongs. Dip the metal in the thermos to warm it up.
posted by fontophilic at 8:06 AM on October 3, 2014 [2 favorites]

For testing the fire team's ability to find hot spots after the (simulated) fire was out, we used beanbags full of rice. Zap it in the microwave and it will show up on infrared for a long time. Nalgene bottles of water work too, but not as well.

Don't microwave the dry rice too long, or your fire might not be as simulated as you wanted, or in the correct location.
posted by ctmf at 8:14 AM on October 3, 2014 [6 favorites]

Use a heating pad like this, safe and effective.
posted by Confess, Fletch at 8:18 AM on October 3, 2014

Note that a webcam is going to have much lower sensitivity to far-IR heat (like a hot rice bag or a heating pad) than the very cool FLIR imager ctmf's fire team is using.

I use a modified webcam that can see near-IR (850nm, in my case) for head-tracking in simulations. Honestly an IR LED (like in a TV remote) hooked up to a battery pack through a resistor will be your best, brightest source. Light bulbs also work, as does the sun, but an IR source that doesn't produce visible light will be a more effective source.

If you want to look at far IR and you have a few hundred bucks, FLIR makes a low-resolution far-IR camera in an iPhone 5 backpack. It's nowhere near as capable as that yellow gizmo in ctmf's picture, but it's a legit thermal camera.
posted by Alterscape at 8:21 AM on October 3, 2014 [3 favorites]

I doubt a modified webcam will see far enough into the infrared to pick up anything is cool enough to be safe. CCD sensitivity drops out around 1200nm. Between around 720-1200 is where you get those cool pictures of trees with white leaves, but thermal imaging is 7000-15000 - far longer wavelengths. With a CCD, you're not going to be able to see thermal radiation from anything much below about 1000 degrees. (A match is about 1200). I think an infrared remote control is probably the best bet - invisible to the naked eye, and bright on the camera.
posted by Nothing at 8:27 AM on October 3, 2014 [1 favorite]

You could get chemical hand warmers at an outdoor supply store.

You could also just plug two 9v batteries into each other.
posted by colin_l at 8:40 AM on October 3, 2014

Seconding the IR flashlight. Use it in a dark room and show the kids how night vision works. Trying to track heat with your webcam will be an ineffective demo.
posted by JoeZydeco at 9:22 AM on October 3, 2014

Paperclip on a 9V battery is dead simple, just don't leave it attached for too long.
posted by odinsdream at 9:28 AM on October 3, 2014

Some cautions. Two 9V batteries plugged into each other can explode. For short periods of time, it's OK. Similarly, shorting the terminals with a heavy-duty wire is also an excellent way to cause an explosion if you leave it there. The amount of energy in a 9V battery is tens of thousands of Joules, equivalent to several bullets worth. That said, a hair-thin filament wire across the terminals should briefly glow red hot before disintegrating and is one of my very favorite demonstrations, surely enough black-body radiation to show up on on your imager. It's safe because the wire can't carry much energy and will fail without generating enough heat to endanger the battery or anyone who happens to touch the wire. You can also make the connection to Edison attempting to make a filament glow long enough for a practical electric light bulb.
posted by wnissen at 9:36 AM on October 3, 2014 [1 favorite]

If just see if any sources like the lights in the building would be enough to work.
posted by AlexiaSky at 9:44 AM on October 3, 2014

I wrote up a bunch about how yeah, near IR basically behaves like visible light, but then I reread your question, and the heated metal should in theory work. Metal (or really most stuff) starts to glow in the visible spectrum around 977˚F. It's emitting a very wide spectrum of radiation, and the peak is WAY off in deep infrared; only the tail is really visible light. But if you heat something to a bit less than that, you can probably get it where no real visible light is coming out, but you can detect a bit with your modified camera.

The absolutely easiest way to get a result is to completely ignore the number 977˚F, and put a light bulb on a variable voltage power supply. Fiddle with the voltage until you can't see the light with your eyes, but can with the camera. This may be an very narrow range of voltage. This technically is heating up a piece of metal where people can't burn themselves, though I admit it's maybe not the most exciting demo.

Those bulbs with the really long filaments that give a very warm light that you see in hip restaurants would probably be good for this.
posted by aubilenon at 11:19 AM on October 3, 2014 [1 favorite]

Could you get a dolls house, rig a bulb inside and then take an IR pic of it, then figure a way to add insulation and take another pic to show the reduced emissions due to hear loss? That way you can show of the IR, show off comparative heat states and talk about how the camera is useful for every efficiency work.
posted by biffa at 1:46 PM on October 3, 2014

You know what puts off a great deal of IR? IR light sticks.
posted by plinth at 5:12 PM on October 3, 2014 [1 favorite]

A cheap battery-powered soldering-iron is ~$12
posted by anonymisc at 5:26 PM on October 3, 2014 [1 favorite]

Thanks everyone. aubilenon's suggestion of bulb + variable voltage is probably just what I need. I want the demo to show how IR vision lets you detect heat, just like some snakes can detect warm blooded prey using their heat pits. That's why the IR remote isn't ideal (since it isn't hot). I'll have a go with the bulb and if it doesn't work, fall back on the IR remote.
posted by beniamino at 12:40 AM on October 4, 2014

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