An old webcam you are not fond of

2 Pieces of polariser, or a totally black exposed negative

Some odd tools

First take the case apart, how to do this will depend on your webcam.

You should find inside a circuit board with a camera assembly on top. There should be a piece that holds the lens, this may screw in and out.

If you unscrew the lens you should reveal the sensor chip, this is the part that converts the image projected on it into electrical signals. Keep this safe and clean.

You are now looking for the IR filter this is a small piece of glass with a reddish or greenish tinge. If you are lucky it will just come off but in this case it is in front of the lens. We had to push the lens out using a soft pencil protecting the lens with some soft polythene.

The filter (top left), lens (top right), and aperture (bottom).

Now you want to put the camera back together in the reverse order you took it apart, without the filter.

You now want a visible light filter instead. you can use a very heavily exposed piece of negative (the parts of a film you exposed when loading the film), or two pieces of polariser aligned so they are opaque to visible light.

Attach the filter to the front of your camera, with some tape, or make some sort of holder for them if you have the technology.

Here we have Ben pointing a remote control at his head.

As you can see in the IR the room is very dark, but the remote control acts just like a torch

In the visible range, turning on this very low powered lamp has virtually no effect on the brightness of the room, compared to the light in the ceiling.  The table lamp uses a conventional light bulb, but the ceiling light uses a compact fluorescent, or energy-saving, bulb.

In the infra red the compact fluorescent is very dim, it doesn't even light up the room. It isn't wasting energy producing light you can't see.

The conventional light bulb on the other hand is probably brighter in the infra red than the visible, so it is is great for our purposes but not very efficient.

A candle is also not very bright in the visible.

But very bright in the infra red, another not very efficient light source.

Plastics that have been coloured with certain pigments become very transparent allowing you to see into this shaver for example.

Similarly cola is relatively transparent at these wavelengths so you can see right through it. If you look at a light through a glass of cola it looks a very deep red, which tells you it's becoming more transparent at the red end of the spectrum, so we shouldn't be surprised that it transmits infra-red light.

Seeing as a laptop screen depends on polarisers to work, which IR ignores, and it is lit by a fluorescent tube it is unsurprising you can't see a picture.

Veins being blue are much more obvious in the IR, it has even been suggested that nurses should use IR cameras to help them find veins to take blood.

If we look outside, most things look similar, but vegetation is much brighter than normal.  Plants can't use IR for photosynthesis so they may as well reflect it to avoid overheating.

Looking at this variegated bush you can see that the presence of green chlorophyll has no effect on the colour of the leaves in the IR.

A perfectly normal 5 pound note.

In the IR you can see that the queen is not all there. It has been printed with two different inks which look identical in visible light, but one of which is transparent to IR as another measure to make them harder to forge.

In a webcam the IR is stopped by the filter, and then there are coloured filters in front of each pixel so the camera can determine colour.

If we put a visible light filter on the camera only the IR can get through which goes through all the coloured filters.

Most webcams use photodiodes as sensors, these have an area in the centre with no fee electrons to carry current.

If light hits the photodiode it knocks an electron off an atom, which can now move carrying electric current