Do LED Bulbs Need a Transformer?

All mains powered LED bulbs require a transformer. Depending on the bulb type, the transformer/driver may be built in to the bulb casing or may be located externally. The purpose of the transformer is to reduce mains voltage (240V) to the desired level relative to the bulb being powered (e.g. 12V or 24V). 

Switching to LED - which bulbs require a transformer?

Most people who choose to switch to LED will do so for domestic use. In most common cases, the housing of the individual LED light bulb will contain the relevant driver suitable to power that bulb. This means that the bulb is ready for use and will not require any further consideration over drivers/transformers. Bulbs that contain an LED driver and may therefore be used without the addition of an external transformer include:

• Bayonet bulb caps (e.g. B22)
• Screw type bulbs caps (e.g. E26, E27)
• Twist and lock style caps (e.g. GU10, GU24)

The reason for describing the transformer as a ’driver’ in relation to domestic LED bulbs is that although the term ‘LED transformer’ has become a popular umbrella term for all drivers and transformers, the term ‘transformer’ should be reserved for larger LED lighting projects requiring a more powerful external supply (see below for further details).

What is the difference between an LED ‘driver’ and an LED ‘transformer’?

When installed between mains power and an LED bulb in an electrical circuit, LED drivers and LED transformers perform the same function (i.e. each serves to reduce the power supply that is fed into the bulb). However, there is a distinct difference between the two electrical components. Mains power voltage in UK homes is around 240V. Given that LED bulbs designed for domestic use require a significantly reduced power supply in order to function correctly over an expected lifetime, a driver/transformer must be installed in the circuit to protect the bulb. The main difference between LED drivers and LED transformers is the power output: 

LED Drivers

Typically, LED drivers are limited to an upper level power output of 100W - 200W. This means that LED drivers are the power supply of choice for small LED lighting setups in the home, as individual LEDs may only require 2V - 4V DC. When LEDs are connected in a series - or ‘array’ - a much higher voltage is required. In this case, an LED transformer may be installed (e.g. to power a light strip). 

LED Transformers

LED transformers are capable of controlling a greater flow of electrical power. Transformers therefore provide the ‘heavy-lifting’ power supply solution for larger scale LED lighting projects such as strip lighting (also known as ‘LED tape’). See below for further considerations over the use of an LED transformer with an LED light strip. 

How far away should I house the LED transformer?

As part of the considerations around purchasing a lighting strip or LED tape, the question over the maximum distance at which the power supply should be housed from the light strip must be addressed. This is because an LED transformer that is connected to the circuit at too great a distance from the LED strip could result in a dip in power supply reaching the strip. Depending on the properties of the electrical cabling connected to the lighting strip (and therefore depending on the electrical load the cable is able to carry), the answers are as follows:

Can multiple LED strip lights be powered by a single transformer?

Yes. Multiple LED strip lights may be powered through a single LED transformer as long as care is taken to ensure that the total wattage demanded by the strips does not exceed the electrical load limits of the transformer. Where the load exceeds the capabilities of the transformer, the output will be affected (likely resulting in dimming or flickering lights). 

Do all LED downlights need a separate driver?

Bulbs intended for use in wet zones (such as downlights in a bathroom) must be IP rated for such use. This means that each sealed bulb will contain a driver, with no external transformer required. The electrical fitting must be considered when installing LED downlights in other areas of the home such as kitchen ceilings - if the fitting is designed to house an MR16 bulb (a double pin bulb), for example, a separate driver must be installed with the bulb. Advice regarding drivers for MR16 bulbs is available from the manufacturer’s product information and from quality vendors of the product at the point of purchase. 

Can I Install an LED Transformer?

Always seek expert advice from a qualified electrician before attempting large scale lighting projects that require the planning and safe execution of an external power supply fed through an LED transformer.