Infrared

Infrared (also called IR) is in the middle of the electromagnetic spectrum:

The wavelength of infrared goes from 1 millimeter to far red light at 750 nanometers (750 billionths of a meter).

Invisible

Infrared is invisible (under special conditions our eyes can see a little into infrared but not well).

light spectrum

So why do hot things glow? Because they are also sending out light:

hot glowing bar

(Note: flames can also have special colors due to chemistry, for example blue and violet flames are due to carbon and hydrogen.)

Heat

We all think that infrared is for heat, but all electromagnetic radiation can heat. For example microwave ovens can cook, laser cutters can cut through steel using light, and so on.

But infrared does cook nicely:

oven chicken

Typically about 2000 Watts of power is used:

Viewing Heat

Special cameras can "see" infrared radiation, and also measure temperatures.

infrared image


We can see the image because the different wavelengths of infrared are changed into visible light by the electronics inside the camera. We call them "false color" images.

Security

infrared security
(the beams are really
invisible)

Security systems use infrared detectors to sense when people enter a room.

And invisible infrared beams get interrupted when someone walks through them, which creates an alarm. (They are low power beams, so people don't get cooked!)

And infrared security cameras can "see" in the dark.

Fiber Optics

Infrared, and light, can be sent along fiber optic cables, carrying information coded into the wavelength.

If the signal weakens it can be boosted using special equipment.

fiber optic
Fiber optic cables

The light stays inside because of a special property of refraction: when the refractive index is lower on the outside, and the angle is not too steep, the light beam has total internal reflection on the inside:

fiber optic bounce
Light bounces off the walls inside the cable

Fiber optics are better than electrical wires which get "noise" (undesirable signals that distort or interfere with the original) from power lines, TV/Radio stations, etc.

Also, many different signals can be sent on the same optic fiber cable (using different wave lengths for example.)

Remote Controls

Many remote controls use infrared at 940 nanometers to send signals to TVs and other devices. The digital signal is sent by little flashes of infrared.

ir remote controls

The signal behaves like light so cannot go through solid things, but can be reflected off some surfaces.

Try seeing if your remote can control the TV by reflecting off a mirror, glass or wall!