Thermal radiationAny object that is hot gives off light known as Thermal Radiation .

The hotter an object is, the more light it emits. As the temperature of the object increase, it

emits most of its light at higher and higher energies.

The Electromagnetic Spectrum

10100

100010000

1000001000000

Wavelength

(nm)

infrared

visible

UV

Black body

A black body is an object that absorbs all light that falls on it. Because no light is reflected or transmitted, the object appears black when it is cold.

A black body emits radiation at a given temperature and wavelength exactly as well as it absorbs the same radiation.

Black body radiation spectrum

Wave length (nm)

Solar radiation – Visible

6000 K

6,000 K 300 K

Radiation from the Earth’s surface –Infrared

Note : To convert to nm multiply by 1000

An image of a human hand taken in the infrared displayed in false color where white and yellow correspond to hot regions, blue and green to cool regions.

IR images

IR Images

Some materials are transparent to infrared light, while opaque to visible light (note the plastic bag). Other materials are transparent to visible light, while opaque or reflective to the infrared (note the man's glasses)

Boy holding cold ball

Boy holding hot ball

The temperature difference between a ball that is cold and one that has been heated. But also note the various warm areas on the boy's face.

IR images

Shown above is an Infrared Map of the Earth. Red areas represent regions of high heat retention in the atmosphere.

IR images

The image shows a cat in the infrared. The orange areas are the warmest and the white-blue areas are the coldest.

IR images