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 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 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?
But What Can You Do With an IR Camera?
Maybe the question should rather be “what can’t you do with an IR camera?” If you get a chance to play with one of these things, you will probably be amazed. We are so used to see the world primarily by reflected light. However, for most objects around us, they emit light in the infrared region. It’s like being in a world where everything is a light bulb.
When you use an IR camera, you literally will see the world in a different light. How about some examples of things you can see.
This is an IR selfie. Two things you can notice here. First, my glasses are dark. That’s not just because they are colder than me, but also because IR light doesn’t go through glass. You are seeing a reflection of the surroundings in my glasses. Now look at my nose. Notice that it’s a little bit darker? You will find that many humans have noses that are colder than the rest of their face. This is probably because I breathe through my nose which cools it off some.
This is an image of the Sun with a couple of tree branches in the foreground. You can’t get an accurate measurement of the temperature of the Sun because this particular camera only measures up to 270 C. What if you measured the sky? You would get a temperature reading of -40 C.
This is a composite image showing both a visible light image and an IR image. Notice that the part of the sidewalk in the shade is much cooler than the part in the sunlight. If you looked closely, you would see that part of the shadow near the sunny part is also warm. This is because the shadow just moved over that part and it hasn’t cooled off yet.
Here are two power adapters for two laptop computers. One computer is asleep and the other is in use. Notice the difference? The one one the right is much warmer. Even the cable is warmer. In fact, these power adapters can get quite warm with use.
Here is both an IR image and a visible light image of the same metallic object. The object has been sitting in the same room for quite some time such that it is at room temperature (just like everything else). You can still see the metal object in the IR because of the surface is reflecting IR light from other sources.
Many attic doors don’t have insulation on them. This means that the cold attic air (this is in the winter) cools off that part of the wood. Notice also the planks that go across for support and the spots where the bolts go through the wood (metal is usually a better conductor of heat than wood). If you look carefully, you can also see the studs through the normal part of the ceiling.
I love this one. It’s a ceiling fan. When you turn these things on, the electric motor gets warm. We always think of fans as making things cooler, but they don’t do that directly. Fans work by doing two things. They circulate the air and the moving air also helps with evaporation. The evaporation cools things down.
How Do You Get Thermal Images?
Unfortunately, you need an IR camera to see this cool stuff. The above images were captured with the FLIR i7. This is a handheld camera that does a fine job. However, it has some drawbacks. First, the price is a bit high at around $2,000 (and this is one of the cheaper cameras). The second issue is the data. You can indeed capture IR images on the i7 which saves these to an SD card. There is also an excellent app from FLIR that allows you too adjust the image after capturing it. That seems nice, but the resolution of these IR images is quite low at just 120 x 120. Finally, the i7 is small, but not "fit-in-your-pocket" small. You can't just carry it with you all the time.
Ok, here is the real motivation for this post. I'm waiting for a new camera, the FLIR ONE. This thing looks super awesome. It's basically an attachment for the iPhone 5 or 5s that allows you to capture IR images. Oh? That's not good enough? Not only will this fit in your pocket, but it won't break your pocketbook. According to this post, the FLIR ONE is only $349. Yup.
You think I should give an official review of this device? I do too. However, I'm still waiting for my review unit. This post will still serve as a good introduction to IR images.
