Lighting Transformers Explained

Transformers are among the simplest, but most useful, pieces of electrical equipment in the world. They were invented in the 1800s and, even though electronics have become remarkably more sophisticated since then, transformers remain largely the same as they have for most of the 20th century. The simplicity of these devices belies the fact that they are capable of actually transforming voltage or current, opening up the possibility of limitless applications.


What are Lighting Transformers?

Lighting transformers are, just as the name implies, transformers that are specifically utilized to work with lighting. They are typically referred to as dimmer switches. By using the ability of a transformer to alter the voltage going through a circuit, a light can be made brighter or dimmer.

According to Networks of Power: Electrification in Western Society, 1880-1930, by Thomas Park Hughes, the Ganz factory, located in Budapest, Hungary, started manufacturing equipment for electric lighting in homes around the year 1878. There were numerous different designs of dimmer switches introduced in the following years, but most of them suffered from flaws related to them being very primitive and early incarnations of these devices.

The initial lighting transformers were primarily designed to make it possible to transform voltage down to levels that were appropriate for household lighting. As the technology developed, however, lighting transformers became more sophisticated and able to scale voltage back or turn it up to make lights dimmer or brighter.


What are the Various Parts Inside?

Transformers are amazingly simple devices. In the simplest sense, a transformer is really made up of two coils of wire. This wire is insulated and, in the vast majority of cases, the two coils are wrapped around a core that is made out of iron, according to How Stuff Works.

There are various types of dimmer switches on the market, but lighting transformers are specific types and not all dimmer switches are actually lighting transformers. Some of them are what are called chopper dimmers, which operate on a principle based on the cyclical nature of AC power rather than on varying voltage.

A lighting transformer is typically an autotransformer, which is a transformer that contains only one winding. Along one side of that winding, called the secondary side, there are a series of taps. In the most basic auto transformer design, the output can be affixed to any one of these taps, which alters the number of windings on the transformer, thus altering the voltage.

In a lighting transformer, there is a variation on the typical autotransformer design. The secondary connection is made via a brush. Because the brush can be rotated over the primary winding however the user wants, the voltage can be varied so that it suits any lighting level that the user prefers. These are essentially infinitely variable devices.


Lighting Transformer Applications

Lighting transformers are used in a variety of different applications, not just for brightening and dimming lights. Essentially, because they do allow the voltage across a line to be varied, they can used for any number of applications where voltage does have to be changed a bit to accommodate various devices.

For example, lighting transformers are sometimes used on small electric motors to provide a way to speed up or slow down the motor, as needed. Lighting transformers are quite often used in households, however, to do exactly what the name implies and provide variable lighting from the same light fixtures.

In practical usage, dimmer switches are sometimes utilized to provide a more pleasant level of light or, if the homeowner prefers, to lower the power of the light when they are away so that there is still light when they get home but so that the lighting doesn't consume a great deal of energy.

It is important to be aware that not all dimmer switches are designed to handle electric motors. According to Epanorama, some dimmer switches can be damaged by attaching these types of loads to them, so it's important to be cautious.


What do the various variables define?

Since most lighting transformers are used in household applications, the variables that apply to lighting transformers are typically very simple. There will be a primary voltage rating, a secondary voltage rating and maximum and minimum power ratings. There may also be a minimum frequency rating and a maximum frequency rating.

These variables need to be adhered to in order to ensure proper function. Failing to do so may not only destroy the transformer, it may also result in fire or other damage to the house in which the transformer is installed. At the very least, it could destroy the electrical equipment to which the transformer is attached, as well, so being safe and sticking within these numbers is sensible.

Primary Voltage Rating

The primary voltage rating is the voltage that can be applied to the primary side of the transformer under normal operating conditions. This needs to be maintained within the stated limits for safety purposes.

Secondary Voltage Rating

The secondary voltage rating is the voltage that will be obtainable from the secondary coil under normal operating conditions with the primary voltage rating applied to the primary coil.


Power Rating

This describes the maximum amount of power that can be applied to the transformer without causing a malfunction or without putting the transformer in danger of malfunctioning. If this number is exceeded, the transformer may overheat or other damage may occur, such as the degrading of the insulation in the windings. Ideally, the entire system to which the transformer is attached should have a lower wattage than the maximum power rating of the transformer itself.


Types of lighting transformers


Electronic transformers are designed for low-voltage applications. These do have some advantages over other types of transformers. They typically operate at lower temperatures and are more compact. These transformers are limited to 300 W of power. This gives them far less power handling capacity than magnetic transformers. Some of these types of transformers incorporate semiconductors into their designs, and many of them alter the load on the leading or trailing edge of the AC power cycle of the power supply to which the lighting is attached.


Isolation transformers separate one circuit from another. They are typically used in applications where sensitive equipment needs to be isolated from a potentially dangerous amount of voltage or current traveling across a primary power source. These types of transformers may be used in lighting applications where there is a very high voltage line involved and where the low-voltage circuit needs to be adequately separated for safety purposes.


Magnetic transformers rely upon the relationship between magnetism and electricity to transform voltage and current. By inducing a magnetic field in the secondary coil, an electrical current is induced in the coil. The number of windings determine the amount of voltage in the secondary coil. On a variable transformer, the brush is used in place of a permanent secondary coil. This creates a transformer where infinite variation in the voltage going across the lighting load is possible. These types of transformers have been in use for a very long time and, over that time, they have become very advanced and efficient.

Dimming Methods

Several different dimming methods are employed in lighting transformers. It's important to remember that not all of these dimming methods actually have to do with the function of a transformer. Some of them have to do with shutting the light off on the leading edge or the trailing edge of the AC power cycle. In such cases, the voltage – or current – is not being transformed in any way, as is the function of a transformer. In those cases, the load of the light is merely being reduced, resulting in a lesser amount of lighting being provided for the room.


Inductive dimming is not commonly used in household applications. Inductive dimmers are installed on the secondary side of a transformer.

Leading Edge

Leading edge dimmers are also referred to as resistive dimmers. These sets of dimmers shorten the AC cycle at the leading edge of the input. This is where the term ''leading edge'' comes from. These are very common dimmers and are used in many households. These are rated by wattage, with 1000 Watts being the highest commonly available variation of these particular dimmers.

Trailing Edge

Trailing edge dimmers are the opposite of leading edge dimmers in that they shorten the AC cycle at the end of the input wave. These are much more complicated than leading edge dimmers and are not nearly as common in household usage. These sets of transformers are quite a bit more expensive than leading edge transformers, but they do have their advantages. They are generally quieter, cooler and more efficient in operation, which makes them desirable, in many ways.

Minimum Load Requirement

Lighting transformers typically need a minimum wattage that they require before they will function properly. As an example of this, if you had a lighting transformer with a minimum load of 60 W and you only had a single 40 W bulb attached to it, the transformer switch would not function as intended.


Dimensions simply refer to the physical size of the transformer. In lighting transformers, this is very important as they need to be installed, quite often, in households. The dimensions dictate whether the transformer will be appropriate for a particular location, though they do not dictate whether or not it would be appropriate for a specific usage.


The depth of the transformer refers to that dimension of the device that dictates how far it needs to be sunk into a wall or how high off the surface it will project. Generally, transformers that can handle larger voltages will have a larger size to them, as well. This will generally be specified on the schematics, making it easier for electrical engineers to decide upon which parts they need.


Again, this merely refers to the diameter of transformer in the physical sense of the term. The transformer obviously has to be of a diameter appropriate for the application.

Maximum Operating Frequency

The maximum operating frequency of a transformer directly affects the core of the device. If the frequency of the transformer is operating at exceeds the maximum rated frequency, excessive current can be induced in the device, causing a great deal of heat to build up and, quite possibly, utterly destroying the transformer itself.

Maximum Temperature

The maximum operating temperature of the transformer describes the highest temperature at which the device can operate without sustaining damage. There is generally a bit of a cushion built into this, but not a great deal. If the maximum operating temperature is exceeded, the device may be completely destroyed and fire may result. Very large transformers have different types of cooling systems attached to them to prevent the maximum possible temperature from being reached, much less exceeded.

Minimum Operating Frequency

Just as is the case with load, many transformers have a minimum operating frequency at which they must function. If they do not operate at least at this frequency, they will not operate properly at all. Most lighting transformers are designed to work within the realistic boundaries of household electrical supplies, so there is no real reason to worry about whether or not the minimum operating frequency will be achieved. In other applications, it may be a concern.

Minimum Temperature

Just as is the case with all other electrical components, transformers have a minimum temperature at which they can be expected to operate properly. If this minimum temperature is not maintained, the device may not operate in a predictable fashion or it may not operate at all. Excessively low temperatures may actually cause damage to the device. In situations where cold temperatures are issues, transformers are typically installed in areas where the climate can be controlled and where they can be prevented from coming to harm due to excessively low temperatures.