There are only two ways you can see something in the world. The first is to have an object that emits light. The light from this object then enters your eye and your brain interprets it. Examples of this type of object are lights and your computer monitor. For all of these types of objects, it doesn’t matter if the room is light or absolutely dark you will still be able to see the light emitting object.
The other (and more common) type of object does not emit light. Instead, to see these objects you need a nearby light source. The light from these sources reflects off the object and then the light enters your eye. Without the light source, there is no light to enter your eye and you can’t see it. Simple right?
Actually, it turns out that all objects are light emitters. It just happens that the light emitted from most objects is not visible to the human eye. Let’s take a look at an example. Here is an ordinary stove top eye. When you first turn it on, it looks just like it did when it was off even though it can get quite hot (don’t touch it!). After the eye gets very hot, it glows with a dark red color.
When objects get hotter, they do two things. First, they emit more light (higher intensity) and second the produce light with a shorter wavelength. Red is the longest wavelength in the visible spectrum (and blue-violet is the shortest visible wavelength). This implies that the much cooler stove eye should be emitting light with a wavelength longer than red light. We call this light infrared.
Here is where the infrared camera comes in handy. The IR camera (sometimes called a thermal imaging camera) can detect this light that your eye can’t see. On top of that, it can look at this light and work backwards to calculate the corresponding temperature of the object. Here are the same stove top eye with an IR camera.
These are called “false color” thermal images. Since our human eyes can’t see IR light, how does the infrared camera display what it sees? It takes each temperature calculation and turns it into a different color. In this particular color palette, brighter and whiter colors represent higher temperatures with the dark blue the colder areas.
There is one important thing to understand. The infrared camera doesn’t always display the actual temperature of the object. Just like visible light, you could have an object that reflects IR light. How is the IR camera to know if this light was emitted from the object or reflected?
This article comes from wired edit released