Infrared Photography Applications

The world of invisible light

The infrared photography applications are numerous and varied...

Long-distance Photography

Infrared photography can improve visibility through certain kinds of haze. This property is particularly important for long-distance photography on the ground where the detail of distant objects is often obscured by haze, and for high altitude photography from the air.

Actually, infrared photography does not always result in a very marked increase in the range of vision, but it generally increases the contrast of the distant subjects and thus the amount of detail that can be seen. This produces the effect of greater penetration.

Photography In the Dark

Since infrared light is invisible, photography in total darkness can be readily carried out if infrared film is used and the light source is covered with a light-absorbing but infrared-transmitting filter.

This property allows infrared photography application for many special purposes and during night time in situations where a bright flash would be disturbing (or betray the photographer) such as:

press photography outdoors in the blackout during war;
detection of intruders and criminals in the dark;
dark adaptation studies of the eye;
photography of wildlife in darkness;
and photography of industrial operations that are carried out in the dark, as in the photographic industry.

Portraiture

Infrared protraits, outdoors or indoors, appear unusual because infrared light causes skin to have a chalky appearance, red lips to appear very pale, and eyes to appear as dark spots. Doctors, however, use infrared photographs for diagnostic purposes.

Survey and Reconnaissance

Infrared photography has been used in forest survey to distinguish between stands of coniferous and deciduous trees. It is also possible to detect the presence of disease in plants and pollution in rivers and other bodies of water.

An important application of infrared aerial photography in war is its use for determining depth of water and detecting underwater obstacles off potential landing places on enemy coastlines. It has been claimed that by comparing infrared and conventional photographs of average coastal waters, depths to 20 feet can be determined to an accuracy of 10 percent.

Infrared photographs have been used for the construction of charts, the study of sandbars and silting of navigable channels, the control of erosion and pollution, the charting of currents, and the study of marine life.

Infrared photography application has also been found in seaweed surveys.

Document Inspection

Infrared photography, particularly infrared fluorescence photography, has found several applications in criminological investigations, and it is a standard tool in many laboratories for:

the study of faded, burned, worn, dirty or altered documents;
the differentiation between pigments, dyes and inks which may appear indistinguishable to the eye;
examination and identification of cloth, fibres and hair;
detection of secret writing, and a variety of other special applications.

Infrared photography has taken a place with chemical, ultraviolet and X-ray study in determining the authenticity of works of art.

Scientific and Industrial

Among the special infrared photography applications, mention can be made of:

plant pathology, in the study of plant diseases where there is change in pigment or cellular material;
paleobotany, particularly in coal petrology;
in the textile field for detection of irregularities to the fibers, particularly where the material is dyed a dark tone and visual examination is difficult;
in photomicrography of deeply pigmented tissues and thick sections, to show enhanced details of internal structure; and in the study of furnaces while they are operating;
in astronomy and spectrography.