Our eyes only allow us to see red through violet "visible
light" (electromagnetic waves with a wavelength between
0.75 to 0.4 microns). We rely upon external light to
bounce off objects (into our eyes). But all the stuff
around us continuously emits electromagnetic energy,
albeit infrared (further than red) light. The warmer an
object is, the more energy it emits. Also, the peak
emission shifts closer to visible wavelengths. Hot
objects can even emit a little visible light, such as a
"red hot" stove.
Stuff around us, including us, emits electromagnetic energy mostly in the 14 to 8 micron range. Our skin is able to detect this thermal energy if it is strong enough - i.e. from a fire, a barbecue, or from our Sun. While we can feel infrared, we can not see infrared. However, an animal such as a pit viper (a rattlesnake is a pit viper) has two pits which are sensitive to infrared or thermal energy. A rattlesnake is able to form low resolution infrared pictures (heat images) of an animal such as a mouse.
Aside from feeling heat on our eyelids, our eyes can not directly detect infrared or thermal wavelengths. However, we can make electronic sensors that can detect these wavelengths. A thermal camera is a camera that is designed to detect this infrared 'light' and convert it to an image we are capable of viewing.
The movie above shows scenes using a visible camera and a thermal camera. First the visible light camera is used to look at a stove top that has been turned on (the movie is sped up so that 40 seconds corresponds to about 4 minutes). As the stove coil heats to about 250 C the coil eventually starts emitting a little bit of red light. While the camera (and our eyes) can detect the red light, we can not see the infrared light.
The same scene is shown with a thermal imaging camera. This camera shows differences in heat. Hotter areas are darker. The second the stove is turned on, the camera immediately shows the heat of the coil, relative to everything else. So much heat is detected by the camera (after about 10 seconds) that it begins to overload the sensor on the thermal camera.
Next side by side is the thermal image of a coffee maker (water is being heated and forced through coffee underneath the black plastic exterior). The visible camera shows no changes, but the thermal camera shows that some areas (especially the top of the coffee maker) are getting warm. At the beginning you can see my arm (which shows up as darker, or slightly warmer than the coffee maker and wall). The pan with hot water, lit up in the thermal camera, is in the background.
Finally, the coffee is poured into a ceramic coffee cup. The hot coffee is clearly visible, and eventually heats the coffee cup.
Again, the visible camera is similar to our eye while the infrared camera is similar to our skin. The infrared camera is sensitive only to the longer wavelengths or what our skin detects as "heat" (the thermal camera is able to detect wavelengths ~ 20 times longer than the visible light camera - electromagnetic waves with a wavelength between 14 and 8 microns).
Side note: The white bar on the left side of the thermal image is the battery indicator. Also, only the top part of the thermal sensor shows hot areas as dark. The bottom area actually shows hot areas as lighter. The thermal imaging sensor relies upon a ferro-electric crystal called Tri-Glycine Sulfate. Since the manufacture of the thermal camera sometime between 1989 - 1999, the sensor crystal now consists of ~ 2 ferro-electric domains (instead of one), one of opposite sign than the other. The images are mostly put in the ferro-electric domain (upper area) that displays hotter areas as darker.
Stuff around us, including us, emits electromagnetic energy mostly in the 14 to 8 micron range. Our skin is able to detect this thermal energy if it is strong enough - i.e. from a fire, a barbecue, or from our Sun. While we can feel infrared, we can not see infrared. However, an animal such as a pit viper (a rattlesnake is a pit viper) has two pits which are sensitive to infrared or thermal energy. A rattlesnake is able to form low resolution infrared pictures (heat images) of an animal such as a mouse.
Aside from feeling heat on our eyelids, our eyes can not directly detect infrared or thermal wavelengths. However, we can make electronic sensors that can detect these wavelengths. A thermal camera is a camera that is designed to detect this infrared 'light' and convert it to an image we are capable of viewing.
The movie above shows scenes using a visible camera and a thermal camera. First the visible light camera is used to look at a stove top that has been turned on (the movie is sped up so that 40 seconds corresponds to about 4 minutes). As the stove coil heats to about 250 C the coil eventually starts emitting a little bit of red light. While the camera (and our eyes) can detect the red light, we can not see the infrared light.
The same scene is shown with a thermal imaging camera. This camera shows differences in heat. Hotter areas are darker. The second the stove is turned on, the camera immediately shows the heat of the coil, relative to everything else. So much heat is detected by the camera (after about 10 seconds) that it begins to overload the sensor on the thermal camera.
Next side by side is the thermal image of a coffee maker (water is being heated and forced through coffee underneath the black plastic exterior). The visible camera shows no changes, but the thermal camera shows that some areas (especially the top of the coffee maker) are getting warm. At the beginning you can see my arm (which shows up as darker, or slightly warmer than the coffee maker and wall). The pan with hot water, lit up in the thermal camera, is in the background.
Finally, the coffee is poured into a ceramic coffee cup. The hot coffee is clearly visible, and eventually heats the coffee cup.
Again, the visible camera is similar to our eye while the infrared camera is similar to our skin. The infrared camera is sensitive only to the longer wavelengths or what our skin detects as "heat" (the thermal camera is able to detect wavelengths ~ 20 times longer than the visible light camera - electromagnetic waves with a wavelength between 14 and 8 microns).
Side note: The white bar on the left side of the thermal image is the battery indicator. Also, only the top part of the thermal sensor shows hot areas as dark. The bottom area actually shows hot areas as lighter. The thermal imaging sensor relies upon a ferro-electric crystal called Tri-Glycine Sulfate. Since the manufacture of the thermal camera sometime between 1989 - 1999, the sensor crystal now consists of ~ 2 ferro-electric domains (instead of one), one of opposite sign than the other. The images are mostly put in the ferro-electric domain (upper area) that displays hotter areas as darker.