I go into more depth of how infrared radiation behaves in my course “The Infrared Photography Masterclass”. But I wanted to present some behaviors in this article as a review.

As with the visible spectrum, radiation in the near infrared portion of the spectrum interacts with various elements and objects such as plants, sky, water, inanimate objects and people. But the unique behavior of infrared radiation with various objects is what makes infrared photography very interesting.

Infrared radiation interacts with healthy plants in an often stunning manner, making for some really interesting images depending on how we process our images. When radiation in the visible spectrum strikes the leaves of a healthy plant, the plant absorbs the blue and red wavelengths but reflects green. This is why many plants appear green to human vision.

However, the radiation of the near infrared spectrum penetrates deeper into healthy plant leaves with a stronger reflection than other objects, such as a tree trunk. This is because plants tend to reflect infrared radiation very strongly, while tree trucks absorb infrared radiation which makes them appear darker. The result is high contrast when plants are illuminated in strong sunlight. Plants have very low tones when in shade, given that much less radiation is reflected while in shade.

Deciduous trees, such as Oak and Maple, tend to produce a bright effect and are usually quite photogenic in near infrared radiation. Plants with large leaves tend to reflect more infrared radiation because they contain more chlorophyll and are thicker.

The leaves of coniferous trees are poor reflectors of near infrared radiation because their leaves tend to be dense and thick. Coniferous trees tend to be dark and shadowy in infrared images.

The earth's lower atmosphere, the troposphere, contains moisture which causes the blue wavelength of the visible spectrum to scatter differently than the green and red of the visible spectrum. This is why we see a blue sky. With infrared photography, a filter above 700 nanometers blocks the green and blue colors of the sky, leaving essentially no radiation striking the camera's sensor in the area of the sky. The dark area of the sky of infrared images does not mean we are "seeing space", although that is often how it appears. There is simply not enough photon energy activating the camera sensor's photosites in the area of the sky within the frame.

Clouds in the sky are accentuated in infrared photography because they are highly reflective of infrared radiation. Because clouds do not normally scatter the colors of the sun, they appear white in human vision. The exception is, of course, during sunset when atmospheric colors affect the clouds. When shooting for infrared, the high reflectance of clouds is often striking, especially against a sky that appears dark or even black. Because the reflectance of the clouds is reduced, clouds heavily laden with moisture appear dark in infrared images, just as they would in color photography.

Due to the high reflectance of clouds in infrared radiation, they tend to appear brighter than in the visible spectrum. This gives them the appearance of more body and dominance in an infrared image. When shooting for infrared with clouds that will have a strong appearance, I like to compose to capture the contrast of the clouds against sky as this image illustrates.

As pretty as this scene may appear after it was processed, this is the image that was output from the camera. This is an example of infrared captures that we often come home with.

When a filter is used that allows some red of the visible spectrum to bleed into the image, such as the 665 nanometer filter used for this image, the scene will be affected by a pink tint until we process the image. It's important to note that there are two factors at play causing this particular tint. First, the 665 nanometer filter is allowing some visible red into the capture. Second, the camera's white balance couldn't be adjusted to the color temperature of this scene.

The appearance of water in infrared radiation is quite interesting. Water tends to appear very dark or even black depending on the angle of the sun. The primary reason for this is that water doesn't reflect radiation in the near infrared spectrum well. Water tends to absorb radiation of the near infrared spectrum. I composed this scene expecting the water and sky to be dark or even black in infrared radiation. I visualized that the trees would contrast white against dark water and sky in the final image. I composed to visually unite the sky and water, although that is not at all what my eyes saw in the actual color scene. What my human vision saw was water with a greenish tint, surrounded by green trees, all of which were under a blue sky canopy. The elements of the scene, such as the sky, trees and water, each had their own color characteristics. Photography in infrared allows us to see our world differently. And that can be very interesting indeed.

Depending on the filter used to cut off the visible spectrum, there is much less energy striking the camera sensor's photosites in the area of the water body. This tends to produce dark tones resulting in very dark or black pixels when water is in the composition.

The very dark or black appearance of water in infrared photography can produce very creative images, given that viewers expect water to have a color, typically with a hue of blue. The blackish appearance of a water body in an infrared shot is perfect for creating high contrast, such as boats, rocks, beach or plant life on or near the water edge, which tend to be high toned.

When shooting for infrared in an atmospheric haze situation, infrared radiation tends to be less scattered by the water vapor in the air. This results in images that seem to penetrate the haze, or that don't reveal the haze as much as a color image would. This image shows how infrared radiation is less affected by the haze. On the day I took this shot, the right half of the trees in the frame of this image were completely hidden from my human vision by the thick haze. While we may not find ourselves taking photographs in heavy haze, it's interesting to see an example of how infrared radiation interplays with elements and objects in hazy situations.

Without an additional light source, such as a flash, the photographic camera captures the radiation from the environment, and records that radiation as it interacts with the various objects in the frame. This is true with color photography as well as infrared photography. The difference, of course, is which portion of the spectrum is being allowed to reach the camera's sensor.

When various objects are present in the frame, such as this image, that has sky, water, land, plant life and metal, the combination of objects often creates very interesting compositions. It is often interesting to play a man-made object off of a nature scene. But with infrared photography you have the added advantage of elements and objects interacting with infrared radiation differently than in the color spectrum. The possibilities for interesting compositions is exciting.

When we compose a photograph in the color spectrum we consider both color and light intensity. And, of course, light will behave differently with different objects in the camera's field of view.

But when shooting for infrared, we need to think more about how the various objects in the frame reflect and absorb radiation, rather than how color interacts with objects. This is why it's important to resist the tendency to think in color when shooting for infrared. In infrared photography, we are interested in radiation intensity, not color. As we discussed in session "What Infrared Photography Really Is" in my course “The Infrared Photography Masterclass”, the camera "maps" radiation intensity to human perceivable tones that, when combined, form an image. Any colors that make it into our infrared images is due to the filter we use or the white balance issue, or a combination of the two. Your primary focus in infrared photography should be how the camera will map tones, not color.

The behavior of near infrared radiation with inanimate objects, such as stone and metal, produces some very interesting effects. Whether the visible or near infrared spectrums, radiation interacts with objects by either reflection or absorption, and usually a combination. Some materials reflect more than others, while some absorb more than others. Stone and concrete, for example, tend to absorb near infrared, resulting in low tones.

The creative possibilities of infrared photography are endless. But, for best results we need to think in terms of radiation intensity, or tones. We must not think in color when shooting for infrared. Shedding the tendency to think in color is a key factor for success with infrared photography. We must also visualize what the scene will look like in infrared radiation because our cameras can't do that for us. This takes practice and experimentation.

Please refer to my course “The Infrared Photography Masterclass” if you would like to learn more about infrared photography.