Posted by jlwile on July 13, 2011
I am working on an elementary science series right now, and I am up the point where I am looking for images to use in the first book of the series. While looking for images that were constructed using infrared light, I came across this one and thought it was really cool (click for credit):
The image is what an infrared camera sees when it looks at a snake wrapped around a person’s arm.
Remember, human eyes are not sensitive to infrared light. However, you can make cameras that see only infrared light. Generally, these cameras show you the amount of infrared light they are seeing by using a color scheme. In the picture above, for example, blue colors mean the camera is receiving a small amount of infrared light, red colors indicate a medium amount of infrared light, and yellow colors indicate a lot of infrared light.
The person’s arm “lights up” in yellow, because he or she is warm-blooded and is therefore warmer than the surroundings. Because of this, energy must flow from the person to the surroundings, and it does so mostly in the form of infrared light. As a result, the person’s arm emits a lot of infrared light. The snake, however, is not much warmer than its surroundings, because it is not warm-blooded. So it doesn’t lose much energy to the surroundings. As a result, it doesn’t emit much infrared light.
Using an infrared-sensitive camera to make such images is called thermography, and it can be used for various purposes, including seeing people in the dark.
Now it turns out you don’t need a thermographic camera to “see” infrared light. A cheap digital camera (like a cell phone’s camera) is sensitive to infrared light and can even take pictures of it. To see this for yourself, get a television remote control and look at the end. You should see a bulb or a glassy area. That area emits infrared light signals, which send instructions to the television.
Aim a cheap digital camera at a television remote control and look at the remote’s bulb or glassy area using the camera’s screen. While you are looking at the camera’s screen, touch buttons on the remote. You will see the end of the remote light up, because it is sending out infrared light, and the camera “sees” the infrared light. If you look at the end of the remote just with your eyes, you won’t see anything. However, a cheap digital camera will “see” the infrared light coming from the remote.
Now you won’t see this effect with an expensive digital camera, but not because the camera’s light-detection system isn’t sensitive to infrared light. It most certainly is. However, expensive digital cameras have filters on the lens that absorb the infrared light before it hits the light-detection system. That way, the camera doesn’t take pictures of infrared light.
If you’ve ever wondered why your phone’s digital camera doesn’t take pictures that are as sharp as your good digital camera, this is one of the reasons. Even if both your phone’s camera and your good digital camera have the same number of megapixels, the pictures from your phone camera seem a bit less sharp than the pictures from your good digital camera, because your phone’s camera is recording infrared light. That adds “noise” to the photo, making it less sharp. A good digital camera filters out that noise, which produces sharper images.