Whether from the sun, fire, electric lights or light-emitting diodes (LEDs), people have never known a world without infrared radiation (IR). It toasts your bread, changes the channel on the TV and bakes the paint on a new car. On the downside, you cannot see IR, and it travels only in straight lines.
The word "infrared" means "below the red," so infrared light has frequencies lower than the red light you can see. This is similar to low sound vibrations you feel rather than hear. Since you cannot see infrared light, most of an incandescent bulb's light is wasted, as is a candle's. You might grab a pan on the stove, not realising it's hot until you burn yourself. Although life might be easier if you could see IR, your eyes are not equipped for it.
Line of Sight
Being a form of light, infrared moves in straight lines. If you've ever used a remote control in a room with furniture, pets and people, you know if anything gets between you and your television, the remote won't work. Scientists call this line-of-sight transmission, meaning you need to see the target to send infrared light to it. If it's around a corner, behind a big dog or beyond the horizon, you are out of luck.
From grade-school science class, you may recall that you can send heat by conduction, convection and radiation. Of these three, radiation is the fastest, moving at the speed of light. In addition to sheer speed, Infrared radiation simplifies heating by removing the need for direct contact between a hot object and the one you want to heat. You can control radiant heat easily by turning the power up or down.
The ease of making and controlling IR is one of its key advantages. You can make IR with fire or a light bulb. Your body produces IR as you sit and read this. The global communications network that powers the Internet depends largely on infrared light made by inexpensive electronic devices.