History of infrared photography
As with any technology, infrared photography has developed a lot since Sir Frederick William Herschel first discovered IR light in 1800. This section will help you brush up on your knowledge of infrared photography history.
Discovery of IR light
Sir Frederick William Herschel, a German-born British astronomer, discovered infrared light on 11th February 1800. While using a variety of colored filters to view sunlight, he observed that some colors passed more heat than others. Herschel hypothesized that the colors themselves may have actually produced different temperatures and set out to test his theory.
Directing sunlight through a glass prism to produce a spectrum, he measured the temperature of each color with a thermometer. From the violet to red parts of the color spectrum, the temperature increased. Herschel then decided to measure the temperature beyond the red-colored light, where there was no sunlight. This area had the highest temperature reading of all, despite being invisible to the naked eye. He named this radiation ‘calorific rays’, however nowadays we call it infrared.
The word infra is a Latin prefix meaning ‘below’ – the radiation is below red in terms of light frequency, which is explained in Chapter 2 – Basic Theory.