|Corky, Matt, and Jared, with the experimental apparatus.|
First, a little bit of background. If you read the previous post by Alex, you'd know that visible light waves are the same kind of waves as radio waves, microwaves, and x-rays; they just wave at different frequencies. Light that has a frequency just below what we can see is called "infrared", which apparently derives from the latin infra--below red (thanks wikipedia!).
So we know that if we get an object hot enough, it will glow visibly. However, warm objects (say, humans, cars, tanks) while not emitting enough visible light to glow, will emit easily detectable infrared light. This makes infrared imaging a handy technology for finding warm things in the dark. And, since many opaque things in the visible are transparent in the infrared (or vice versa), you can dream up a lot of fun to be had if you could only see in the infrared.
Well, it turns out that the CCDs in many common webcams are sensitive to the infrared (IR). However, since an infrared signal would make for a weird looking visible light picture, it is simply filtered out. Well, we (mostly Matt) got our hands on such a webcam, for a whopping 3 dollars, and removed the filter. Then we turned the tables, and inserted a visible light filter. For this we used the darkest part of a developed film roll, and while not getting rid of all the visible, it did a pretty good job with the lights down low. You can get a junk roll from your local Rite Aid photo center for free, just ask for Sue. She is very helpful.
So we took some pictures of whatever we could find that was a strong IR source. It turns out that our particular camera wasn't sensitive to detect the signal of a warm human (or a cold one for that matter).
We had to get something just a little hotter. So we lit a stick on fire, and then blew it out. Here's what it looks like in the now very pedestrian visible spectrum, with the lights out:
It's just barely glowing. Now, let's look at it in what I'll call "enhanced" visible with the lights on, meaning that it's sensitive to both IR and visible at the same time.
The infared obviously dominates the output. It looks like an IR sparkler. Now, let's shut the lights off, and see only IR:
It's bright enough to "light up" my hand, which it certainly couldn't do in the visible. Okay, so we had to light this thing on fire, and it was already glowing. Well, my response to that is...this spoon:
Normal spoon. But actually we heated it up a bit on the stove. Here it is in enhanced visible:
And now, lights off, infrared only:
Apparently we only heated up the tip significantly.
Now, we have a super high tech flashlight that has three modes. It can produce green LED light, white LED light, or incandescent white light. Corky pointed each one at me. White LED light, visible:
Creepy, eh? It's the shaved head.
Now, white LED light in the IR:
Nuthin' doin'. Similarly for green LED light. This is included only for its creepiness. First, in the visible:
Corky calls this "the most palatable [pronounced incorrectly] picture of Jared we could find." In the IR, nada:
But for incandescent white, in visible:
I am aglow! Matt is clearly shocked. This happens because light generated by LED's occurs because of electrons hopping around semi-definite energy states of a material, making semi-definite frequencies of light. However, incandescent light is due to the filament being glowing hot, emitting radiation over a wide range of frequencies, and we know that it's got a strong contribution in the IR.
So much for hot things. You have a bunch of IR dedicated sources around your house that maybe you didn't know about. One such source is many TV remote controls. Here we are, in the visible, with the lights low, pointing remotes at our faces.
This is actually a promo pic for our 80's new wave band. Here's what this looks like, with buttons depressed, in the IR:
A personal favorite.
These remotes weren't the brightest source we could find. It turns out that the Wii sensor bar (which actually transmits, rather than receives data) is a freakin' beacon (say that out loud). Here it is, on top of our TV, which Corky is apparently flying towards.
Unassuming little guy in the visible. But with the Wii on and in IR mode:
There's a person in there too, IR bathing. But I promised you translucent Snuggies. (Yes, we own a Snuggie, and highly recommend them.) Here's Matt hiding behind one, whilst I angrily supervise:
Now, let's look behind the curtain with IR:
Look, I told you it was a Snuggie, the sleeve is visible!
Now, if we had more resolution, we could even pick out a person in a dark room, and look at the temperature variations of objects. However, with approximately an hour of fiddling and 3 dollars, I think we did pretty good. We're not hard to entertain, but this definitely did the trick.