SHOWALL FUN PRANKS HIGH VOLTAGE LAZARUS-64 PHOTOGRAPHY SPY GADGETS VIDEO GAME
Figure 2 - Infrared LEDs offer various lens types as well as wavelength and output power
Figure 2 - Infrared LEDs offer various lens types as well as wavelength and output power

At the top of the LED, the thickness and shape of the plastic casing forms the optical properties of the output lens. A wide angle lens allows the light to cover a larger area over a given distance, whereas a narrow angle lens allows a brighter beam to reach a further point. For TV remote controls, a medium angle is a good tradeoff between distance and viewing angle, but for night vision, a wider angle is usually better. In this project, I am using typical 940 nanometer TV remote type LEDs with a narrow field of view. You can see in the images that the resulting beam is sharp and focused much like a small flashlight.

If you are planning to use your night vision system indoors in a small area such as a room, then try to match the field of view to both the camera and the LEDs so that you can illuminate the entire scene. For a portable or head mounted night vision system, a narrower beam may work better as this will give you more light as you look around the darkness. The three LEDs shown in Figure 2 have different colored bodies, but all of them are basically the same as far as specifications. The black body on the LED shown in the right of Figure 2 is actually completely transparent when viewed with a video camera as the plastic has been manufactured to pass only infrared light, light that we cannot see. Field of view, power output, voltage, and wavelength are all specifications stated on the datasheet, so consider these when sourcing new infrared or visible light LEDs for any project.



Figure 3 - To make an LED emit light, it must be connected with proper polarity
Figure 3 - To make an LED emit light, it must be connected with proper polarity

A new LED that has not had its leads trimmed will have one lead longer than the other, and this lead will be the positive lead. If you are salvaging your parts from an old circuit board, than lead identification will be impossible, but the good news is that there are two other ways to identify the polarity of the LED. If you look at the underside of the LED, one side of the round base will have a flat side near one of the leads to indicate that it is the negative lead. Also, the negative lead will be connected to the larger cup shaped carrier inside the lead as shown in Figure 3, although you may not be able to see through all of the various plastic colors.

You can make a very easy LED tester that will check the polarity and functioning of all visible color LEDs by simply keeping a 3 volt coin battery (such as a CR2450) on hand to drop across the leads. If you connect an LED backwards, it will not give off any light. If you connect it properly, it will visibly light up as long as the wavelength falls in our human range. The 3 volt lithium coin battery has such low internal resistance, that it cannot damage an LED, even one rated for less than 3 volts, so it makes the perfect tester for all visible LEDs. To test an infrared LED, you will need to view the output from a security camera on a video monitor.

Back Home Last Next
You are Viewing... Page 2 of 10
Lucid Science Electronics from the Fringe AtomicZombie Hack-a-day SparkFun