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LEDs Explained: A Guide to Light-Emitting Diodes

SMD LED
SMD LED
SMD LED REAR
SMD LED Rear markings
Through hole LED
Through hole LED
LED colours
LED Colours

Introduction

Welcome to our guide on LEDs! Whether you are a curious beginner or an experienced user, understanding LEDs (Light Emitting Diodes) over incandescent bulbs can be incredibly beneficial to modellers. Below, we will look into what LEDs are, how they work, and the advantages of using them.

LEDs come in a range of shapes, sizes, and colours, offering modellers and designers flexibility in creating lighting solutions for model railways and other hobbies. Most LEDs can be dimmed, controlled digitally, and even integrated into smart lighting systems for enhanced functionality and efficiency.

Most importantly, LEDs can be used with good results in model railways. Whether it is street lighting, building lighting or loco and coach lighting, LEDs can be used to create many lighting effects which will add to and improve the viewing experience.

Considerations before using LEDs in your model railway

There are several considerations to be mindful of when installing LEDs in model railways to ensure optimal performance and realism. Here is a guide covering key aspects:

Voltage and Current Requirements: LEDs typically operate at low voltages, commonly around 2-5 volts for standard LEDs, and there are others rated at 12v. Ensure that your power source (battery or transformer) matches the voltage requirements of your LEDs. If not, you may need to incorporate resistors or voltage regulators to avoid damaging the LEDs.

Standard LEDs are sensitive to excessive current. To prevent overloading and burning out your LEDs, you will be required to incorporate a current limiting resistor into the circuit. Calculate the appropriate resistor values based on the LEDs forward voltage and desired current using Ohms Law (V = IR), more of which later

Scale and Size Considerations: Choose LEDs that match the scale of your model railway. Larger scale layouts may require larger LEDs to maintain realism, while smaller scales like N or Z may benefit from tiny surface-mount LEDs for more accurate representation.

Space Constraints: Consider the available space within your model railway for LED placement. Opt for compact LEDs or surface-mount LEDs (SMD) where space is restricted, ensuring they fit seamlessly into your scenery without obstructing movement or visibility.

Wiring and Connection: Use an appropriate wire gauge for connecting LEDs to your power source and control circuits. Thicker wires with lower gauge numbers are preferable for longer runs or higher current applications to minimize voltage drop and ensure reliable performance.

Polarity: LEDs are polarity sensitive, meaning they must be connected with the correct orientation (anode to positive, cathode to negative). You must pay particular attention to polarity when wiring your LEDs to prevent reverse connection, which may damage them.

Lighting Effects and Control: Implement methods for adjusting the brightness of your LEDs to simulate different lighting conditions or create dynamic effects. This can be achieved through using a PWM (Pulse Width Modulation) dimming circuit or variable resistors.

Flicker and Effects: It is possible to mimic realistic lighting effects such as flickering lamps, fading signals, or flashing beacons using specialized LED, LED controllers or microcontrollers like Arduino. These can add depth and authenticity to your model railway scenes.

Environmental Considerations: LEDs produce less heat compared to traditional bulbs, but excessive heat build-up can still affect performance and longevity. Ensure adequate ventilation and heat dissipation in enclosed spaces to prevent overheating of LEDs and associated components.

Moisture Resistance: If your model railway is exposed to humidity or moisture, choose LEDs rated for outdoor or damp environments. Ensure you seal wiring connections and exposed components with waterproofing materials such as heat shrink tubing or insulation tape to prevent corrosion and electrical problems.

Testing and Troubleshooting: Before final installation, thoroughly test each LED and its circuitry to ensure that it functions correctly. Check for correct wiring, polarity, and brightness consistency across multiple LEDs.

Troubleshooting Tools: You should equip yourself with a few troubleshooting tools such as a multimeter which will help diagnose connectivity issues, faulty components, or short circuits. Be prepared to troubleshoot and repair LED circuits as needed during and after installation.

By considering these factors and taking appropriate precautions, you can effectively incorporate LEDs into your model railway layout, enhancing realism and visual appeal while ensuring reliable performance.

What are LEDs?

An LED, which stands for Light Emitting Diode, is a tiny device that gives off light when you pass electricity through it. It is like a little bulb, but much smaller and very much more efficient. LEDs are used in all sorts of things and are becoming more popular in lighting effects for railway modellers. They come in a wide range of different colours, such as red, blue, green, yellow and white, and they use less energy and last longer than traditional incandescent light bulbs.

Here are some key characteristics and features of LEDs:

Efficiency: As we have already mentioned, LEDs are highly energy efficient compared to incandescent bulbs. They convert a higher percentage of electrical energy into light, resulting in less heat, lower energy consumption and lower operating costs.

Longevity: LEDs have a much longer lifespan compared to conventional light sources. They can last tens of thousands of hours or more, reducing the frequency of replacements and maintenance.

Instantaneous Operation: LEDs light up instantly when powered on, unlike some other types of lighting that may require a warm-up time.

Compact Size: LEDs are available in various sizes and form factors, including small surface-mounted devices (SMDs) and larger high-power packages. Their compact size and low profile make them suitable for a wide range of model lighting applications including building and rolling stock lighting.

Colour Options: LEDs are available in a wide range of colours, including red, green, blue, yellow and white. They can also be manufactured to emit specific wavelengths of light which further enlarges the ranges available.

Dimming and Control: Most LEDs can be easily dimmed and controlled using electronic dimmers and controllers. This allows for dynamic lighting effects and energy savings by adjusting the brightness according to the desired level.

Environmental Benefits: LEDs contain no mercury or other hazardous materials, making them environmentally friendly. Additionally, their energy efficiency helps reduce greenhouse gas emissions associated with electricity generation.

Due to their numerous advantages, LEDs have become increasingly popular for various lighting applications, including residential, commercial, industrial, and outdoor lighting, as well as in automotive, signage, and display lighting. They are also now more popular in a wide range of hobbies, including model railways, than older type bulbs.

What makes LEDs different colours?

LEDs produce different colours of light through a process called electroluminescence, which involves the emission of photons (light) when electrons recombine with electron holes within the semiconductor material of the LED. The specific colour of light emitted by an LED depends on the materials used in the semiconductor, particularly the band gap energy of the materials.

Here is how LEDs produce different colours:

Material Composition: The colour of light emitted by an LED is determined by the semiconductor material used in the LED construction. Different semiconductor materials have different band gap energies, which correspond to different wavelengths of light. For example:

Gallium nitride (GaN) is commonly used for blue and white LEDs.

Aluminium gallium indium phosphide (AlGaInP) is used for red, orange, and yellow LEDs.

Indium gallium nitride (InGaN) is used for green and blue LEDs.

Doping: Doping is the process of intentionally introducing impurities into a semiconductor to alter its electrical properties. By selectively doping different regions of the semiconductor material, manufacturers can control the band gap energy and thus the colour of light emitted by the LED. For example, adding a small amount of indium to gallium nitride can shift the emission from blue to green.

Phosphor Conversion: In white LEDs, blue or ultraviolet (UV) light is typically emitted from the LED chip itself. This blue or UV light then excites a phosphor coating on the LED, which converts some of the blue or UV light into longer-wavelength light, such as yellow or red, resulting in a broad spectrum of visible light that appears white to the human eye.

Colour Mixing: In some cases, multiple LEDs of different colours are combined to produce a desired colour output. For example, red, green, and blue (RGB) LEDs can be combined in varying intensities to produce a wide range of colours through additive colour mixing. This technique is commonly used where in models lights need to change colours depending on direction.

By controlling the materials, doping levels, and phosphor coatings used in LED manufacturing, it is possible to produce LEDs that emit a wide range of colours, from ultraviolet and blue to green, yellow, orange, red, and even white.

Colours of LEDs

LEDs are available in a wide range of colours, including:

Red: This is one of the most common colours for LEDs. Red LEDs are often used in panels, model car lights and model traffic signals.

Green: Green LEDs are also quite common and are used in display panels, colour light signals, and sometimes in outdoor lighting applications.

Blue: Blue LEDs are used in a variety of applications, including panel displays, as lights on emergency vehicles and welding simulators.

Yellow/Amber: These LEDs are commonly used in model traffic signals, panel indicators, model car turn signals and emergency warning lights.

White: White LEDs are popular for general lighting purposes. They are used in everything from headlights on cars and locomotives, building interior lighting and welding type simulations.

Orange: Orange LEDs are used in model vehicle indicators and emergency vehicle warning lights.

Purple/Ultraviolet (UV): These LEDs can be used in special applications where an unusual type of illumination effect is required such as moving water and some building illumination.

Pink: Pink LEDs are used in decorative lighting and some artistic applications.

RGB (Red, Green, Blue): These LEDs can emit a wide range of colours by combining the light from red, green, and blue sources. They are used in panel displays and other applications where dynamic colour control is desired.

These are just a few examples, and there are many more variations and shades available depending on the specific needs of the application.

What is the difference between common cathode and common anode LEDs

The key difference between common cathode and common anode LEDs lies in how their internal connections are made. Here is a breakdown of each:

Common Cathode LED (Negative): In a common cathode LED, all the negative (-) terminals of the individual LEDs are connected together.

To light up an individual LED within a common cathode LED, you connect its positive (+) terminal to power while the common negative (-) terminal is connected to ground.

Common Anode LED: In a common anode LED, all the positive (+) terminals of the individual LEDs are connected together.

To light up an individual LED within a common anode LED, you connect its negative (-) terminal to ground while the common positive (+) terminal is connected to power.

In summary, the main difference between common cathode and common anode LEDs lies in the polarity of the electrical connections: in common cathode LEDs, the cathodes are connected together, while in common anode LEDs, the anodes are connected together. The choice between common cathode and common anode configurations depends on the specific requirements of the application and the desired method of controlling the LEDs.

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 it has 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 from behind a solid panel and the light shows to the front. 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 one. The resistor is soldered into the positive leg and is fully insulated for safety. 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 than 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 and they come in and generally have a low voltage requirement. These LEDs will 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: 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.

SMD LEDs

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.

Unlike through-hole LEDs which are sold by their size, SMD LEDs are given numbers to designate their different sizes, usually a four digit number. The first two digits represent the package size of the SMD LED. This size is usually expressed in millimetres and refers to the length and width of the LED package. For example:

0805: 8.0mm x 5.0mm
1206: 12.0mm x 6.0mm
3528: 3.5mm x 2.8mm
5050: 5.0mm x 5.0mm

Types of SMD LEDs: 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 eyesight and a steady hand.

Strip LEDs: These innovative light strips consist of high-powered SMD LEDs of different sizes 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 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 LEDs: COB or Circuit on board LEDs are very similar to SMD LEDs but they contain 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 of multiple LEDs connected in series, on or in, a 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.

Wiring LEDs which DO NOT require a resistor: The LEDs we list with the 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 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.

What wire should be used when wiring LEDs: When wiring single through-hole LEDs, the wire size primarily depends on the current flowing through the circuit and the distance between the LED and the power source.

Determine the maximum current rating of all the LEDs in the circuit. This information is typically provided on the LED listing page on the website. For standard through-hole LEDs, typical currents range from around 5mA to 30mA per LED.

Consider the voltage drop along the length of the wire, especially if the distance between the LED and the power source is significant. Use a wire gauge that minimizes voltage drop to ensure proper operation of the LED.

Once you have that information, select a wire from our listings that will carry the maximum power requirement for your lighting circuit. Generally, a 7/0.2 wire will suffice as it has a maximum current rating of 1.4amps. If the current is higher than 1.4amps increase the size of the wire to a 16/0.2 wire.

When joining wires to LEDs ensure adequate insulation by either using insulation tape or preferably heat shrink tube of the correct size.

If electrical safety precautions are taken your wiring should be safe and stay reliable for many years.

Do all LEDs require resistors?

Not all LEDs require a resistor, but many do. It depends on the LEDs specifications and the electrical characteristics of the circuit in which it is being used.

LEDs are voltage-driven devices, meaning they require a specific voltage (typically referred to as the forward voltage) to operate. They also have a maximum current rating beyond which they can be damaged. If the voltage applied to an LED exceeds its forward voltage without any current limiting mechanism (such as a resistor), excessive current can flow through the LED, potentially causing it to fail.

Whether or not you need a resistor depends on the specifics of your circuit:

Low Voltage Applications: In some low-voltage applications, such as battery-powered devices with a voltage close to the LEDs forward voltage, a resistor may not be necessary if the voltage source can already limit the current within the LEDs safe operating range.

High Voltage Applications: In circuits where the supply voltage is significantly higher than the LEDs forward voltage, a resistor is typically required to limit the current and protect the LED.

Constant Current Sources: In some cases, instead of using a resistor, LEDs are driven by constant current sources or LED driver circuits that automatically adjusts the current to maintain a consistent brightness level.

However, in most common applications where the LED is powered by a voltage source, it is advisable to use a resistor to limit the current. This ensures the LED operates within its safe limits and prolongs its lifespan.

In which lead should the resistor be fitted

A resistor should be connected in series with the LED, regardless of whether it is connected to the positive or negative lead. However, in most cases, it is common practice to connect the resistor to the positive lead (anode) of the LED. This is because it helps ensure that the LED does not conduct current until a sufficient voltage is applied across it, which is the typical operating condition for LEDs.

Here is a simple explanation:

Resistor in Series: Placing the resistor in series with the LED helps limit the current flowing through the LED. This is crucial because LEDs are sensitive to excessive current and can be damaged if the current exceeds their rated value.

Positive or Negative Lead: While it is technically feasible to connect the resistor to either the positive or negative lead of the LED, connecting it to the positive lead is more common. This is because the positive lead (anode) is typically the side where current enters the LED. By placing the resistor on this side, you ensure that current is limited before it reaches the LED.

Current Limiting: The resistors role is to limit the current flowing through the LED to a safe level. This prevents the LED from burning out due to excessive current. The value of the resistor is chosen based on the LEDs forward voltage and the desired operating current.

Remember to calculate the resistor value based on the specific LED forward voltage and the desired operating current to ensure proper functionality and longevity of both the LED and the circuit.

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.

While you do not necessarily have to use a special power supply designed specifically for LEDs, using one can offer several benefits, as mentioned earlier. However, it is possible to power LEDs with a variety of power sources, depending on the specific application and requirements. Here are some options:

Standard DC Power Supply: LEDs can be powered by a standard DC power supply, such as a battery or a DC power adapter. However, it is essential to ensure that the voltage and current output of the power supply are suitable for the LED requirements, and a current-limiting resistor may be necessary to prevent over current.

AC/DC Adapter: Many LED lighting products come with AC/DC adapters that convert mains AC voltage to the appropriate DC voltage required by the LEDs. These adapters often provide regulated output voltage and current suitable for powering LEDs safely.

LED Driver: As mentioned earlier, LED drivers are specialized power supplies designed specifically for powering LEDs. They offer features like constant current regulation, voltage regulation, and protection mechanisms, making them ideal for driving LEDs efficiently and reliably.

Solar Power: LEDs can be powered by solar panels and batteries in off-grid or outdoor lighting applications. Solar charge controllers are often used to regulate the charging of batteries and supply power to the LEDs.

Dimmers and Controllers: In applications requiring dimming or colour control of LEDs, specialized dimmers and controllers are used in conjunction with power supplies to achieve the desired lighting effects.

Ultimately, the choice of power supply depends on factors such as the specific requirements of the LED lighting system, the desired level of control and efficiency, and the available power source. While specialized LED drivers offer advantages in terms of efficiency, regulation, and control, it is possible to power LEDs with a variety of power sources depending on the application.

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 are no exception. Each LED listing shows the specification of the item on the page. This shows things like the 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
Wavelength: 625. - This is 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.

Further information on LEDs and their uses in railway modelling

Click the button below for even more help and advice on LEDs. The next page is a continuation of this page and explains more about white LEDs and more on safety.