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In infrared photography, the film or in this case the image sensor used is sensitive to infrared light. The part of the color spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for photography range from about 700 nm to about 900 nm. An “infrared filter” is used; this lets infrared (IR) light pass through to the camera, but blocks all or most of the visible light spectrum (the filter thus looks black or deep red).
When these filters are used together with infrared-sensitive sensors, very interesting “in-camera effects” can be obtained; black-and-white images with a dreamlike or sometimes lurid appearance known as the “Wood Effect,” an effect mainly caused by foliage (such as tree leaves and grass) strongly reflecting in the same way visible light is reflected from snow. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not glow under infrared.
The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds stand out strongly.