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Lighting LEDs

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Before using an LED as a light detector, observe the light produced by LEDs.

Materials

    One Red and one near infrared LED
    1.5 volt battery (AA or AAA)
    Battery holder with wire leads (or 2 6-cm long copper wires)

What to Do...

Start with the red LED.

Connect one 1.5 volt battery to the LED. Battery’s positive end connects to the LED’s longest wire. Battery’s negative end connects to the LED’s shortest wire.

NOTE: LEDs may be damaged or destroyed by using more than one battery in series or by connecting them in reverse with the positive charge going to the longest wire of the LED. It is customary to use a red wire to connect to the positive end of a battery and a black wire to the negative end. When properly connected, light will be emitted from the LED’. Notice what part of the LED is brightest. See top photo on right.

Now the IR LED. Repeat the procedure above.

Do you see anything emitted? Does the LED get warm when hooked up? Did the Red LED? How can we see if it works?

Interestingly, a digital camera can detect IR. Use a digital camera with an LCD screen to detect IR. Turn the camera on, point it toward the top of the IR LED after the battery is connected. What do you see?

If you have a TV remote control handy, try pointing it toward the camera, press a button on the remote control. TV remotes work by sending out pulses of IR to an IR LED on the TV which converts the light pulses to electrical pulses. See bottom photo on right.

Next: Measure Angle of Sensitivity

Diagram of how to light an LED bulb
This picture was taken before we destroyed several LEDs (and warmed some fingertips). Use only one 1.5 volt battery!
Digital photograph of a near infrared LED lit by a battery.
Digital photograph of a near infrared LED lit by a battery.