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The Easy Guide to Light-emitting diode:



An LED (light emitting diode) is an absolute treat for any modeller. It satisfies some very important requirements:

  1.  Uses very little power. A typical white LED runs on a current of just 0.02 Amps (20mA) and consumes just 0.066 Watts (66mW) so it will last for 200 hours on a 6V 4Ah battery!

  2. Runs cold, unlike a traditional grain of wheat type bulb, an LED generates almost no heat, so you can safely mount it in plastic / balsa etc.

  3. Easy to wire up

  4. Cheap to buy, when bought from us a white LED which is one of the more expensive types is only 20p when you buy at least 10.

  5. Lasts almost indefinitely. The life expectancy of an LED is around 100,000 hours (over 11 years) so you can safely glue it in & never have to worry about getting it out again.


So what more could you want? There are just a few simple wiring considerations that need to be taken into account – there had to be some sort of catch!

An LED is polarity sensitive & so will only work one way round. It also requires a fairly specific voltage – too low & it won’t light, too high & you’ve killed it! Just to make it a little bit more awkward the different colours of LED require different voltages. If this is beginning to sound complicated, don’t worry, just read on.


LEDs come in all manner of shapes and sizes, but essentially the only difference electrically is down to the colour – to create the different shapes, the manufacturers simply encase the LED itself into different shapes of plastic. There are also 2 different brightness classifications for LEDs, generally referred to as “standard brightness” and ultra-bright” the standard types generally have coloured housings, whereas the ultra-bright ones generally have water clear housings – this gives the maximum possible light output. These LEDs will give a fairly well defined beam of light, but this can easily be altered – if the surface of the LED is rubbed with a fine abrasive paper it will give it a diffusing effect, making it good for interior lighting. The domed end of the LED can be carefully cut or filed off to give a wider beam dispersion – with just a little experimentation you can get a whole range of different effects.


The best way to use an LED is on a voltage that is higher than it needs & add a resistor in series to drop the voltage to the desired level.

LED soldering guide

The following example uses a 6V battery, but you can easily use any other voltage of battery or power supply, just swap the 6.0 in the following equation, for the voltage you are using to work out the resistor that you would need.


50 x (6.0 – LED Voltage) = Resistor required


This table shows the LED voltages for the different colours:














Standard brightness














So for a white LED, this equation becomes…..


50 x (6.0 – 3.3) = 50 x 2.7 = 135 Ohms


In some cases like this, you may get a resistor value that is not commonly available, in these cases simply increase the value to the nearest one that is available. For instance here you would use a 150 Ohm resistor.

If you want to use several LEDs, then you can just use multiples of the circuit just shown, or if the voltage is high enough you can do the following: (PTO)

LED soldering diagram

To work out the resistor here, our equation becomes:


50 x (Battery voltage – 1st LED Voltage – 2nd LED Voltage) = Resistor Value


So if we now assume that we have 2 red LEDs connected to a 6V battery & add these numbers to the equation we get:


50 x (6.0 – 2.0 – 2.0) = 50 x 2.0 = 100 Ohms


Using this method you can add more LEDs to the chain as required, the only limitation being that the battery voltage must be greater than the combination of LED voltages otherwise they will not light.

If you find that the brightness is too high, then simply replace the resistor with one of higher value, this will take some experimentation to get the desired brightness level, but another beauty of the LED over the grain of wheat bulb, is that it keeps its colour as it is dimmed down. Whereas a grain of wheat bulb when dimmed would go from white, to yellow to orange etc a white LED  will simply stay exactly the same white colour, just not as bright.

In order to simulate the yellowish-white that you would get from a tungsten bulb, there are LEDs with a yellowish white colour.

The connections to the LED are best made by soldering wires to them. The LED legs can be cut down to make them easier to install – just remember which is which as the LED will not work if connected the wrong way round!

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