What are Infrared Rays and What are infrared rays used for?

We cannot see infrared rays, but we can feel them as heat.
It is the infrared rays in sunlight that help to make us feel warm when we stand in the sunshine.

Anything that is warm also gives out infrared rays. 

Some animals, such as rattlesnakes, can detect infrared rays given off by other living things.
This helps them to catch their prey.

Some burglar alarms work by detecting the infrared heat given off by burglars when they have broken into a building. These alarms have to be carefully adjusted so that they aren't set off by the infrared heat from smaller animals, such as cats!

Photographs can be taken in complete darkness by using infrared sensor, which is sensitive to infrared heat rays. This type of sensor takes a "heat picture" instead of a light picture. The photograph is then printed in visible colors so that we can see what is in the picture.

Infrared rays are used in medicine.

Special infrared photographs of the body, called thermograms, can show up diseased parts because they radiate more heat than healthy parts.

Infrared rays are also used to treat muscle pain.

A heat picture of the land taken from the air shows different patches of color. These colors are not the land's real colors. Instead, they represent different amounts of infrared heat radiating from the ground. The picture can also reveal diseased crops. 

Dead or dying plants emit fewer infrared rays than living plants, and this shows up as a particular color in the photograph.