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 2 - Infrared LEDs offer various lens types as well as wavelength and output power