A Light emitting diode (LED) is an electrical component that emits light when a current is passed through it.LEDs will only pass current in one direction (that is what a diode does) so you need to make sure you wire them up properly or they wont work.LEDs are perfect for mighting models. In the days before LEDs filming models were lit with regular bulbs and/or neon bulbs.These generated significant heat and required high voltage pwoer supplies. The filiming model of the Millenium Falcon had real fans installed under the grills on the top of the hull to keep the model cool when the engine lights were lit. The filming model of the Enterprise D made for Star Trek The Next Generation had neon lighting for the nacelles and apparently could give you a nasty shock due to the high voltage required to power the neon lights.

LEDs offer many benefits for lighting;

They are very bright

They have a low voltage requirement

They draw very little current

They last a long time

They dont generate heat

They are small and come in many different colors


There are two kinds of LED.Through the hole LEDS have 2 wires that are used to solder the LED to a circuit board with holes predrilled. SMD (Surface mount diodes) LEDS are much smaller and are designed to be mounted directly to the surface of a circuit board.You can buy SMD leds that have wires soldered on to them already so you dont need to attach them directly to a circuit board.You can also buy SMD LEDs that are soldered to a backing strip creating a long strip of LEDs.


LEDs have some characteristics that you need to understand so you choose the correct LED for your project.These are the main things you need to look at;

Forward voltage

Forward current

Luminescence

Viewing angle


The forward voltage is a measure of how much the voltage drops across the LED.We need to know this number because if we provide less than the forward voltage the LED will not light.if we are connecting LEDs in series we also need to know the total foward voltage of all of the LEDs because that number must be less than the voltage we are providing to the LEDs.

The forward current rating is the maximum current that the LED can handle.IF you provide too much current across the LED it will burn out instantly.If we know the forward voltage, the voltage of the power and the current rating of the LED we can calculate the resistor we need to use to protect the LED.

Forward voltages are different for different colored LEDS.Forward current is based on the size of the LED, not the color of the LED.

Luminescence is a measure of the bright the LED is at its rated current.It is measured in millicandela (mcd). The highe the mcd the brighter the led is.You can also vary the brightness of an LED by lowering the current across the LED.

Viewing angle.LEDS have a lens above the semiconductor that focuses the light.This is encased in the plastic covering.Some LEDs have a very narrow viewing angle to concentrate the light into a narrower beam.These LEDs are used for flahslights or spotlights. Other LEDS produce more diffuse light.There are generally called "diffused" LEDs in the description and they are in many cases what we want to use to light a large area inside a model.


Unless you have a very simple set up with a 3v battery and a couple of LEDs you will need to add resistors to your LEDs to limit the current that goes across the resistor. if we look at a 3mm LED is has a current rating of 20 ma. So we must make sure that the current coming from the power supply (which will be several hundred ma) is reduced to a maximum of 20ma before it reaches the LED.


You can buy prewired LEDS that have everything already done for you.You just have to select them based on the volatge you are planning to use.I will briefly discuss how to figure out which resistor you need if you want to buy bulk LEDs and resistors.

SMD LEDS were designed to be soldered directly onto printed circuit boards.They are very very small and bright.Thye are perfect for lighting models where you have very limited space. You can buy them in bulk with no wires , but be warned soldering wires onto SMD LEDs is quite challenging. The best opiton is to buy prewired SMD LEDS.

SMD LEDs some in a variety of sizes, but be warned it is VERY confusing with 2 different kinds of number classifications.Again the ones that are prewired are preferable and many vendors classify them according to size ranging from 0.6 mm to 5mm. Most of the prewired SMD LEDs have resistors already attached-You just have to select the ones with the correct voltage rating for your project.

SMD LEDS are also used to make LED strips.LED strips are a bunch of SMD LEDS wired in parallel on to a backing board.

I would briefly like to talk about some special LEDs before we move on to how to wire them.

The way of the LEDs we are talking about are either off or on.If you provide power to them they turn on and when you turn the power off they turn off. For some models this is fine.But what happens if you want to add blinking or flashing or flickering lights such as navigation or strobes on a USS Enterprise build or pulsing engines? There are 2 ways to achieve these special effects.You can either use circutry to control the power supplied to the LEDs or you can use prewired LEDs that have the circutry already installed either on the LED itself or in one of the wires of the LED.

You can buy prewired LEDs that blink off and on.You can buy prewired LEDs that will flicker to mimic a flame and you can buy breathing/fading LEDs that pulse.These are all very useful in making a more dynamic lighting for your model and they dont require and special circuitry or microcontrollers.



These are basically 3LEDs in one casing .They have 4 wires.One for each of the red,green and blue cathodes and a common anode.You can vary the brightness of each individual color to make any color you want.RGB LEDs usually require a microcontroller to control them.

Wiring LEDs in series is very simple.You connect the anode of the first led to the positive from the power supply.You then connect the cathode from the first LED to the anode of the second LED and so on.... LEDS in series are great for very tight spaces where you dont have much room for wires.You need to add the current resisting resitor to the circuit.It doesnt matter if you put the resistor on the anode side or cathode side of the circuit.

In series ciruits each LED gets the same current so they will all be the same brightness.The voltage is divided between the LEDS. The practical upshot of this is that the power supply voltage MUST be larger than the sum of the forward voltages of the LEDs.This is a significant problem in many cases because generally we use fairly low voltage pwoer supplies for models.Even if you use a 12V DC pwoer supply you cannot use more than 6 red LEDS in the series circuit because when we add the forward voltage of the 6 leds we get 12V.