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Figure 0 - This project will explore several ways to convert visible light into infrared light
This project will explore several ways to convert visible light into infrared light

Although infrared LEDs are the most common source of invisible light for a night vision device, they are certainly not the only option available, nor are they always the best. Depending on your camera type and setup, you may need a hand held source of infrared light that can be rapidly moved around the scene, or possibly an infrared light source that differs in wavelength from the standard 800 nanometer to 950 nanometer wavelength of the standard infrared LEDs.

Infrared light falls just below red on the light spectrum, making up the wavelengths from about 750 nanometers to about 1500 nanometers. This light cannot be seen by human eyes, but it can easily be seen by most video cameras, making it useful as a covert lighting method in night vision systems. Some video cameras can even see part of the ultraviolet light spectrum from 200 nanometers to 400 nanometers. That will be covered here as well. The goal will be to pass white light through various materials that will attempt to block out all of the visible light and only pass the light that is invisible to the human eyes, yet visible to most security cameras and spy cameras.



Figure 1 - Infrared pass filters can be made from many different materials
Figure 1 - Infrared pass filters can be made from many different materials

A filter that blocks out all light except for the small portion of the spectrum that falls between 800 nanometers and 1000 nanometers is called an infrared pass filter. This effect is exactly the same effect seen by placing a colored lens over your eyes to see the world in a different color tone. If you place a green piece of translucent plastic over your eyes, the world will look green because only the light from the 490 nanometer to 560 nanometer wavelength will reach your eyes. An infrared filter will do the exact thing, but since you cannot see infrared light, the filter material will seem completely dark to your eyes. When you place an object made of translucent infrared material in front of a video camera, it will look completely clear, as if the camera has some special ability to see through a solid object.

This infrared pass filter effect can be exploited to create a very powerful infrared illuminator by passing white light through the filter to extract and send out only the infrared light that the video camera can see. The benefit to this approach over using infrared LEDs is that a very small and powerful illuminator can be made, as well as a very large and extremely bright illuminator. The objects shown in Figure 1 all exhibit some infrared passing abilities, which will be explored using a small black and white security camera and some white light from an incandescent flashlight bulb.

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