What you Need
What to do
First of all, this experiment has a high probablility of damaging your webcam beyond repair, so please use an old webcam and don't complain to us if it breaks.
The sensor in a webcam is sensitive to both visible and infra red (IR) radiation so the manufacturer adds a filter to stop the IR, otherwise it would produce unexpected results when it took photos. So we want to remove this filter and replace it with one that stops visible light but allows IR through.
What may happen
As we have seen in another kitchen science, a remote control looks different in the infra-red. This adapted camera is much more sensitive and so you get a fascinating view of the world...
First we had a look at some light sources:
Objects in the Near Infra Red
Then we had a look at some objects...
As is possibly obvious, we at the Naked Scientists found this absolutely fascinating, and I would strongly recommend you opening up a old webcam if you have one you are not attached to!!
Why does it happen?
Your webcam has a sensor behind the lens which is sensitive to most colours of light and IR (and also ultra violet). It has a filter on the front which stops the IR, and then a series of filters on the sensor chip itself to only allow one colour through to each sensor on the chip so they can detect different colours.
When we just let IR into the camera by putting our filter on the front it will pass through all the coloured filters to slightly varying degrees, as these filters are not designed to stop it.
Why is my webcam sensitive to IR anyway?
Webcams detect light by having lots of small sensors on a piece of silicon. Each of these sensors is a small diode - a one way valve for electricity, and the electronics is trying to push electricity the wrong way through this diode.
This normally doesn't work because a diode is designed so that there are no free electrons to carry an electric current when you try and push electricity the wrong way. But if a photon of light with enough energy hits the middle of the diode it will knock an electron off a silicon atom which can now move and carry electric current. The electronics then measures this current and so how much light has hit the sensor.
Any colour of light above the mid infra red (so near IR, visible, UV etc) will have enough energy to do this, so your camera is sensitive to infra red light. More expensive CCD chips found in real digital cameras work slightly differently but on the same principle, so they are also sensitive to IR.
I've lots of experience with infra-red cameras. Most black and white "security" cameras don't have any IR-blocking filter, so you don't need to take them apart. Just add a visible-blocking filter (black exposed negative film etc) as described.
I'm a science teacher, this is a fantastic thing for me in the classroom. Works great! thanks guys. One word of warning if any other teachers plan to use it in class. I pointed it at my wife and her bra showed up straight through her otherwise opaque top. Might get yourself into some trouble and cause some significant embarrassment if you go pointing it at girls. Suggest if using it in class you keep it away from the girls.
Monochrome Infra-red film for 35mm cameras is available while stocks last ...
Old webcam stripped down and ready, now i only have to find the drivers for it!
I have no idea what the software is doing. What does the result look like? Does it work when the room is dark and you illuminate something with a remote control, or is it just an aesthetic thing? daveshorts, Tue, 29th Jan 2008
I have a 'night vision' on my webcam, but all that is is a row of leds beneath the camera that illuminate the subject, so there is no actual light detection outside the visible spectrum. I cannot say if this is anything like what your webcam is doing. another_someone, Tue, 29th Jan 2008
I also bought a cheap 'night vision' webcam. All it is, is a webcam with some high intesity LEDs that kick in when it gets dark.
At long last, I have my infra red camera working...and working well.