LEDs How they work and how they can be used Beginners Guide | Railwayscenics
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About the LEDs that we sell

SMD LED Rear markings
2 smd leD REAR
Through hole LED
Through hole LED
LED colours
LED Colours


I hope here to describe and explain a little about the LEDs that are sold on our website. There are many types, sizes and colours of LEDs and it can be confusing so hopefully this will not confuse further. LED technology is continually advancing so the products need to do so also.

What are LEDs?

A light-emitting diode (LED) is a special kind of diode that glows when electricity passes through it. LEDs can be bought in a range of colours. They can also be bought in forms that will switch between two colours, three colours or emit infra-red light.

LEDs are quite different to light bulbs. Light bulbs are designed to work on a voltage, and can work on almost any sensible DC voltage if you have the correct value resistor fitted. LEDs are polarity sensitive and will only work when correctly wired. The cathode is normally indicated by a flat side on the casing and the anode is normally indicated by a slightly longer leg. On SMD LEDs there are painted marks to designate the cathode and anode. Wiring with the wrong polarity will not harm the LED, as long as the maximum voltage has not been exceeded. LEDs also give off no heat when lit and use minimal power. Used properly LEDs have life expectancies in the tens of thousands of hours. They will far outlast an miniature incandescent bulb and usually the life of the modeller. This makes them far more efficient than older style incandescent light bulbs.

Colours of LEDs

LEDs come in many colours. The colours are created by changing the semi conducting element inside the actual LED. The two main types of LEDs presently used for lighting systems are aluminium gallium indium phosphide alloys for red, orange and yellow LEDs, and indium gallium nitride alloys for green, blue and white LEDs. Slight changes in the composition of these alloys changes the colour of the emitted light.

We currently sell a range of LEDs which are available in blue, green, orange, red, yellow, cool white, warm white and natural white. To confuse things even further each of the colours are also available in different outer packages. These outer packages can be diffused (coloured), milky white (white) or water clear (clear). The colour of the outer body of the LED does not affect the brightness of the LED output. There are also LEDs with different brightness. The brightness is usually measured using a luminosity intensity rating which on our site is the figure after Lum. int. The higher the figure the brighter the LED.

The LEDs that we sell

Before we dispatch any LEDs, we test them to ensure that they operate and that the colour is what has been ordered. The only way to return a faulty LED is when its been working and in operation for a while and it fails.

We sell two main types of LEDs. These are SMD LEDs which generally, are soldered to circuit boards, and are much smaller than other types, and through hole LEDs which are what most people associate with LEDs. These are generally called through hole LEDs as they are mounted through holes. Each of these types is available in a range of different voltages, colours and styles. Within these types they can again be split into those that DO require a resistor, and those that DO NOT. All of our LED listings will tell you whether a resistor is required, and what value resistor will give the best light. If you already have resistors, please make sure that they are the recommended value or higher.

Within the above types, we also have versions of some LEDs that come pre wired and fitted with a resistor if the LED requires. The resistor is soldered to the positive leg and is fully insulated for safety, and then wires are attached which are between 150 and 200mm long. The wires are colour coded and generally the red wire is the positive and the black wire the negative. In some cases the wires are colour coded to the light output of the LED where the LED has more that one colour.

Types and sizes of through hole LEDs

Sizes of through hole LEDs

Through hole LEDs are available in a range of sizes. Our website currently lists 1.8mm, 2mm, 2.4mm, 3mm and 5mm LEDs. These LEDS are also available in the following types.

Standard LEDs

These LEDs are available in a range of colours and have a constant light output regardless of the type of outer package they come in and are generally have a low voltage requirement. These LEDs do require an inline resistor for correct operation.

Flashing LEDs

Flashing LEDs are used as attention seeking indicators without requiring external electronics. They look the same as standard LEDs but they contain a built in circuit that causes the LED to regularly flash with a typical period of one second. In diffused lens LEDs, this circuit is visible as a small black dot. Most flashing LEDs emit light of one colour, but more sophisticated devices can flash between multiple colours and even fade through a colour sequence using RGB colour mixing.

Flickering LEDs

These LEDs look the same as standard LEDs but instead of having a circuit that regularly flashes the light, they use a different circuit to produce a candle type flickering effect which can be used to simulate a flickering fire, ash pits or even gas type lamps It is also possible to use a flickering white LED with a flashing white LED to produce a welding effect.

Bi Colour LEDs

Bi colour LEDs incorporate two different LED emitters in one case. They consist of two dies connected to the same two leads. Current flowing in one direction emits one colour, and current in the opposite direction emits the other colour. All you have to do to get the two different colours is to reverse the voltage through the same wiring.

Tri colour LEDs

The name is a bit misleading as the LEDs usually still only contain two colours but use a common anode or cathode. This gives the LED three wire connections instead of the usual two. In most cases a tri colour LED contains two individual LEDs with a common cathode/anode connection on the centre leg. Each of the internal LEDs can be lit individually by connecting either anode/cathode (outside pins) offering either of the two colours. A third colour (a mixture of the two individual colours) can be obtained by connecting both anodes/cathodes to a positive supply.


RGB LEDs come with red, green, and blue emitters all in the same housing, in general using a four-wire connection with one common lead (anode or cathode). These LEDs can have either common positive or common negative leads. Some only have three leads and the third colour is obtained by joining two of the other colours. There are also RGB colour changing LEDs that have just two connections and automatically cycle through the range of colours.


Surface Mount Device LEDs are very small and also come in different packages, sizes and types like the through hole LEDs described above. As they are so small, they have lots of uses within modelling hobbies for things like model vehicle lighting where space is limited. They are also available in a full range of colours, types and sizes just like the through hole versions.

Types of SMD LEDs

Unlike through hole LEDs which are sold by their size, SMD LEDs have a number allocated which describes the size. We sell 0603, 0805, 1206, and 3528 types. There are others, but we shall not complicate things too much and will only deal with the ones that we sell. These different types are also available in the same range of colours and types as the through hole LEDs. Our product descriptions give all the information we think is required to enable you to select the right product for the job. Being so small means that it is very difficult to solder small wires to this type of LEDs. You need good eye sight and a steady hand.

Strip LEDs

These innovative light strips consist of high-powered SMD LEDs of different size and colours mounted on a super-thin flexible circuit board with an adhesive coating on the rear. These strips have many uses from lighting models or to whole layouts. They generally do not need any resistors fitting as they are included on the circuit board, and they can be bought to work on 3v, 5v, 12v, 24v and 220v. The strips may also work with a dimmer unit. Strips can usually be cut into shorter lengths as long as they include a complete circuit, usually in threes. We sell some strips that can be separated into individual LEDs. These strips are normally 8mm wide but we do have some 5 and 4mm versions available.


COB or Circuit on board LEDs are very similar to SMD LEDs but they contain a larger clusters of smaller LEDs giving off more light using less power. COB chips typically have more than 9 diodes all connected to a single circuit with only two connections. This simple circuit design is the reason for the panel like appearance of COB LED lights. SMD lights appear like a collection of smaller lights. They are available with a solid or flexible backing. These COB LEDs are available in different colours and different shapes for different applications.

Filament LEDs

LED filament bulbs are sold as replacements for normal filament bulbs, but it is possible to use the filaments in models. The LED filament is made up from multiple LEDs connected in series, on or in, flexible or rigid transparent substrate. Depending on the original voltage of the bulb you may need to fit resistors inline so the filaments operate correctly. Just handle them carefully, as they are fragile and easily broken.

Wiring and using LEDs

Unlike light bulbs LEDs will only work when connected properly and will burn out if the maximum voltage is exceeded. If our product listing says you need a resistor, that is the minimum size required for a particular voltage. It is possible to decrease the brightness of an LED by increasing the resistor value up to a point where the resistor value will be so high it reduces the voltage so much the LED will not light. To keep things simple, we recommend using one resistor per LED, but it is possible to use one resistor for several LEDs.

Power supplies for use with LEDs

It is possible to use many things to power LEDS. From batteries up to desktop PSUs. I generally use a plug-in power supply of 1 or 2 amps to power mine on a layout or display. Being plug-in devices, they are safe to use as long as you do not overload a socket or extension lead.

How many LEDs can I wire together?

We spend a long time writing our product descriptions so they contain all the information that is required for you to choose the correct product for your specific application. The LED pages is no exception. Each LED listing shows the specification of the item on the page. This shows things like voltage required to light the LED, brightness, power usage and the viewing angle.
IFmax: 30mA. - This is the current required to light the LED
VFtyp: 11.5. - Shows typical voltage required
VFmax: 14V. - Maximum voltage that should be applied to the LED.
Lum. int (mcd)@ IF; (9v): 20. - Brightness of the LED
View angle: 40deg. - Best angle to view the LED light from
Wave-length: 625. - This is basically the colour

From that specification above we can see that the IFmax is 30mA or 0.030 amps, so if you had a 1amp supply you could use 33 of the same specification LEDs. Without going over the maximum rating of the power supply.

Wiring LEDs which DO NOT require a resistor

The LEDs we list with a voltage mentioned already contain a built-in resistor. These LEDs are generally rated up to a maximum of 14 volts, and this should not be exceeded or damage may result. They will work down to a voltage as low as 9 volts. If you have a supply that will exceed the voltage then it is possible to add in a series resister just to lower the voltage.

Wiring LEDs that DO require a resistor

Resistors are relatively inexpensive and basically restrict the current passing through the LED, as the LED has no current limit itself. If you put an LED on a battery with no resistor it would be extremely bright for a fraction of a second before it blows.

Each LED should have its correct resistor wired to either terminal, but it is preferred to use the positive connection. Only one resistor per LED is required. All of our LEDs that require resistors have various resistor values listed and the voltages for that resistor. As long as you use a resistor with a value higher than that listed for your voltage, the LED will be fine. It is possible to slightly increase or decrease the brightness of an LED by changing it's resistor.

It is not necessary to supply a separate feed to each resistor and LED, but they are best wired in parallel, rather than in series.

How can LEDs be used in Railway Modelling?

I see no reason why LEDs of some sort cannot be used to light buildings and rolling stock interiors and exteriors. They can be used in street and platform lighting. They can be used in locomotives as head and tail lights. They can be used in small vehicle as front and rear lighting. The special effect ones can be used to simulate flickering fires in steam locomotives or even house fireplaces, bonfires and barbeques. The bright white ones can be used to simulate a welding effect without the need for circuits to create the flashing or flickering effect. The diffused ones can be used in control panels to show points settings, or whether a circuit is switched on. The strips can be used to illuminate whole layouts rather that spot lights or fluorescent tubes. I am sure there are more uses such as powering fibre optics to get really small beads of light, but that I will leave to your imagination.

Resistor calculator.

Some of our stocked LEDs require an inline series resistor to reduce the current flowing though the diode. We do list some of the minimum value resistors that can be used at some of the more common voltages used in railway modelling on the product listings, but there may be instances where you are using a different supply voltage. We have therefore added a page to the website where you can add in the required information and the resistor value will be automatically calculated for you. Saves lots of maths. The required values are all given on the LED product page, so all you need is the input voltage.

See the calculator at our LED CALCULATOR PAGE.


Hopefully after reading the above you know a little more about LEDs. They are better to use than the old style incandescent light bulbs in many cases as they use less power, give off no heat and will last for years. They are not that expensive to buy, and prices are becoming lower. The wiring for an LED is no more complicated than for a light bulb, so there is no real reason not to use them.

Good luck and try to use LEDs where you can. If nothing else you may help save the planets energy consumption just a tiny bit.

To see all of our LEDs please visit our LED CATEGORY PAGE.