Invisible infrared light illuminating the landscape
In digitalinfrared photography, the image sensor used is sensitive to infrared light (unlike a traditional camera where an IR blocking filter is placed in front of the sensor inside the camera). The part of the infrared light spectrum used is referred to as near-infrared to distinguish it from far-infrared, which is the domain of thermal imaging. Wavelengths used for near infrared photography range from about 590 nm (some merge of colout from the visible light spectrum) to about 900 nm (black and white only. A modified infrared DSLR camera is sensitive to infrared light.
When a modified DSLR infrared camera is used “in-camera effects” can be obtained; false-color or 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. There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs. The effect is named after the infrared photography pioneer Robert W. Wood, and not after the material wood, which does not strongly reflect infrared.
The other attributes of infrared photographs include very dark skies and penetration of atmospheric haze, caused by reduced Rayleigh scattering and Mie scattering, respectively, compared to visible light. The dark skies, in turn, result in less infrared light in shadows and dark reflections of those skies from water, and clouds will stand out strongly. These wavelengths also penetrate a few millimeters into skin and give a milky look to portraits, although eyes often look black.
Over the years I have used several “modified” DSLR cameras to capture infrared images including various Canon and Olympus cameras. Currently I use Sony cameras and have 3 “modified” cameras with different wavelength conversion.