Smoke, which is made up in part by soot and water vapor, scatters visible light and obscures the view.
Infrared light passes through the fine particles in smoke, providing a clear view.
Our eyes are unable to detect all forms of light.
Human eyes have evolved to detect the rainbow of colors that make up visible light. Some objects, like stars and light bulbs, emit their own light. Other matter, like plants and animals, can be detected because they reflect visible light from other sources.
Visible light is only one form of light. There are other types of electromagnetic radiation that human eyes cannot see. Objects that do not give off their own visible light (and are therefore invisible to our eyes in the dark) can glow in other wavelengths, like infrared or ultraviolet. The entire range of light, from radio waves to gamma rays, is known as the electromagnetic spectrum.
Here, a firefighter stands in a room filled with smoke, which obscures what can be seen in visible light. However, when we switch to an infrared light view, it is possible to see through the smoke. Human eyes can’t see infrared light without the assistance of tools, like a specialized camera, but we can feel it as heat. And since wavelengths of infrared light are longer than those of visible light, they pass through the smoke, which is why they provide a clear view of the setting.
Also known as: Electromagnetic radiation
Type: Infrared and visible light
Size: We can describe light waves in terms of wavelength, or distance from one wave peak to the next. Visible light waves are shorter than infrared light waves.
Did you know: All forms of light travel at the same speed (the speed of light) through a vacuum, but they carry different amounts of energy. Radio waves are the lowest energy. Gamma rays are the highest.
Find out more with these additional resources from NASA’s Universe of Learning
Visible light image: NASA, IPAC, Pasadena Fire Department
Infrared light image: NASA, IPAC, Pasadena Fire Department
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This product is based upon work supported by NASA under award numbers NNX16AC65A and NNX15AB26G and contracts NAS5-26555 and NAS5-03127. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.
Slider Interactive: A comparison of two images of the same scene showing a firefighter standing in a smoke-filled room. One image shows visible light; the other shows infrared light. Below the caption is a horizontal slider bar with two labeled stops and a solid white circle. Dragging the white circle right and left along the slider bar causes the image, labels, and caption to change. The change gradually occurs as the image, along with its associated caption and labels, fades out and the other fades in. A toggle button at the upper right of the photo turns the image labels off and on. The labels are in the form of text with arrows pointing to specific features in the images.
Color photograph of a fully-equipped firefighter standing on the left, looking into a smoke-filled room. The firefighter is partially obscured by the smoke and no details are visible in the room.
Smoke, which is made up in part by soot and water vapor, scatters visible light and obscures the view.
Image of infrared light from the same scene, shown as a range of color and brightness from almost black (dark) to brown, red, orange, yellow, and white (bright). The firefighter, who is clearly visible on the left, glows orange, yellow, and white against a somewhat darker orange background. The oxygen cylinder on the firefighter’s back is dark brown to black. The rest of the room, which was obscured by smoke in the visible light image, now shows some detail, including hints of furniture, walls, doorways, and lights. A person, who glows bright yellow to white, is lying on the floor. Fine details are not visible, but it is clear how the person is positioned and that they are wearing clothes and shoes.
There are three text labels in this stop. The dark-colored equipment on the firefighter’s back is labeled “Cold oxygen tank.” A face mask, which is bright yellow-white, is labeled “Breathing apparatus.” The bright person lying on the floor is labeled “Actor in training exercise.”
