SHOWALL FUN PRANKS HIGH VOLTAGE LAZARUS-64 PHOTOGRAPHY SPY GADGETS VIDEO GAME
Figure 4 - A typical LED datasheet showing the important parameters
Figure 4 - A typical LED datasheet showing the important parameters

When hunting for new LEDs from any manufacturer, you will need to refer to the datasheet in order to choose the appropriate LED for the job. The most important specifications will be: peak wavelength in nanometers (nm), field of view in degrees, output power in millicandela (mcd), and forward voltage and current. There are many other specifications that you may also need to know such as peak pulsed current limitations, package size, and lead type. Also note that the brightness of an infrared LED is usually not rated in millicandela as that is a rating for visible light. Infrared LED brightness is specified as optical power output in milliwatts per steradian (mW/sr). The LEDs I am using in this project are very common TV remote types, and have the following ratings; 950 nm wavelength, 1.2 V forward voltage, 100 mA forward current, 250 mW/sr output power.



Figure 5 - Some infrared LEDs include a band pass filter in their casings
Figure 5 - Some infrared LEDs include a band pass filter in their casings

To the human eye, the 950 nanometer infrared LEDs shown in Figure 5 look completely black, even when held up to a bright light source, but when viewed by a video camera, appear perfectly clear, even when not powered. The reason the camera can see right through the LEDs is because the plastic is made up of materials that only pass infrared light, creating a band pass filter that blocks most of the light that is not within the specified wavelength. So, if this LED was outputting light between 800 and 1000 nanometers, the band pass filter may help cut all unwanted light except for the output close to 950 nanometers as specified in the datasheet. Other LEDs are perfectly clear, or have slightly blue tinted plastic bodies.

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