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Figure 0 - Infrared LEDs are invisible to humans but visible to security cameras
Infrared LEDs are invisible to humans but visible to security cameras

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 many video cameras, making it useful as a covert lighting method in night vision systems. A common example of infrared light is the medium for communication between your remote control and television set. The LED on the end of your remote sends out pulses of infrared light which is received by the infrared detector on the TV and demodulated back into data. Of course, you cannot see the pulses because they are out of our visual range, but any video camera that is not equipped with an infrared filter can see this light easily.

There are many good quality security cameras available on the market that include a low lux video camera in a weather proof housing along with an array of infrared LEDs for night vision applications. Of course, you may want to just make your own simple infrared illuminator for projects that you need to add night vision to. This can be done in a few hours with a few dollars worth of infrared LEDs. Black and white security cameras and small board cameras are particularly sensitive to infrared light. These ultra low lux cameras can usually be purchased for about $100 or less, especially from online sellers. Add 10 or more infrared LEDs, and you now have a night vision system that is better than those that were selling for thousands of dollars in the 1980s.

This project represents the most basic LED illuminator possible, and is nothing more than a series string of LEDs running from a DC power source or battery pack. You can build this infrared illuminator from a single LED and coin battery, or add as many LEDs as your power pack can handle. With 10 LEDs, you can easily light up a room for a video camera, and with 100 LEDs, you could light up your entire yard to make is seem like midday to a security camera. Our Night Vision Viewer projects also use infrared LEDs as an invisible light source.



Figure 1 - Your TV remote control communicates over an infrared light beam
Figure 1 - Your TV remote control communicates over an infrared light beam

The most basic example of infrared illumination can be found at the end of your TV remote control. This 940 nanometer infrared LED is pulsed on and off at 40 Kilohertz to transmit the control codes to the infrared light receiver in the appliance. Take a look at the LED and press the button in the remote. You will see nothing, even though the light from the LED is probably as bright as the light from a white LED keychain flashlight. Now, if you view this LED light through a monitor connected to a video camera, it will look very bright on the screen. You might also be able to see the light through the viewfinder on a camcorder, but it will become a very dull purple glow due to the infrared filters being used to correct the color balance.

There are several varieties of infrared LEDs, ranging in size, field of view, output power, and effective light color. The most commonly used infrared LEDs output 940 nanometer infrared light which is far beyond the human visual range, and fairly detectable by any non filtered video camera. There are also infrared LEDs available for the 800 to 900 nanometer range, and these are even better for use in night vision applications, but there will be an ever so slightly detectable red glow as the human eye can faintly detect this band of light. If you have seen an outdoor night vision security camera after dark, then you are probably familiar with this dull red glow. The TV remotes shown in Figure 1 all have 940 nanometer LEDS, whereas my huge collection of night vision LEDs are designed to output 850 nanometer light.

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