Simple LED Lightsource
The right choice of LED and battery can be combined to make a very simple light source.
LED Blue or white work best but all visible colors will work. The LED should be one with long leads, at least 2 cm long.
Battery 3 volt disc type Lithium for example #2032
Broccoli rubber band (A short fat rubber band that fits tightly around the Lithium battery. Or the neck cut from a balloon.)
Optional a piece of paper about 2.5 cm x 5 cm and a binder clip shown here.
Wrap the rubber band around the battery.
Slide the legs of the LED between the battery and the rubber band.
Notice the LED has a long leg and a short leg. The long leg must go next to the positive terminal of the battery.
Optional Place the LED leads on each side of the battery, cover both sides with paper. Clip the assembly together with a binder clip.
To Do and Notice
Notice that the LED glows.
Normally LEDs are designed to run with 20 mA of current.
This is usually achieved by using a battery and a resistor. For example a 9 volt battery and a 470 Ohm resistor.
However, LEDs have a band gap, in Blue LEDs this band gap is about 2.5 volts.
In the simplest model of an LED, his band gap is subtracted from the voltage of the battery leaving only 0.5 volts to create a current.
In the more complex model of the LED the current is an exponential function of the voltage. And the combination of a 3 volt battery and a blue LED creates about the right current.
White LEDs usually operate by combining a blue LED with a yellow phosphor.
Red and Green LEDs have a band gap below 2 volts. This leads to currents that are slightly high. However in practice these seem to work just fine.
To turn off the LED run the leads outside of the paper.
This lightsource is perfect when you need a small easy to build source of light.
However using rechargeable batteries is better for the environment. You can also use two rechargeable AA or AAA batteries in a holder.
Since the holder will require some soldering go ahead and add a 220 ohm resistor in series if you use a red or green LED.
Making a holder for the light.
A magnet hot-melt glued to PVC can be used as a simple LED mount.
A simple holder can be made by taking a connector for 1/2 inch or 3/4 inch PVC schedule 40 tube and inserting a piece of tube into the holder.
A magnet can be hot-melt glued to the top of the tube.
The magnet is used to hold the binder clip of the simple LED.
Scientific Explorations with Paul Doherty
10 December 2014