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LED downlights in halogen Banner Photo courtesy of Pexels by Milly Eaton

Why You Shouldn’t Install LED Downlights in Halogen Fittings

You’ve finally seen the light.

Like millions of other like-minded electricity consumers, you have come to the conclusion that the best way to conserve energy, save on electricity bills and maintenance costs is to adopt LED technology.

Your newly purchased bulbs signal that big plans are afoot and you can’t wait to install LED downlights in your existing halogen fittings.

Don’t. You could be about to make a mistake that will take time and money to undo.

To understand why fitting LED bulbs in halogen fittings is not recommended, you need to know how halogen and LED applications work.

How LED Downlights Work

LED downlights produce light when electrons move on a semi conductor, a process known as electroluminescence.

Unlike the halogen lamp which has a filament, LEDs have a cathode and anode enclosed in a plastic envelope through which voltage is applied.

The electrons are pumped up to a high energy.

In their effort to go back to their original state, they produce packets of energy called photons which present different colours depending on the temperature level at the time of combustion.

Even after they age, (usually 25,000 hours of use) LEDs will still maintain 70% of the initial brightness.

Electroluminescence is landfill-friendly since no hazardous materials are used in LEDs, it utilises low wattage and results in a longer lifespan than incandescence.

How Halogen Downlights Work

Halogen downlights emit light through incandescence.

Halogens have a tungsten filament in a high pressure gas-filled bulb. Its contents are then enclosed in fused quartz aluminosilicate which is stronger than the glass in standard incandescent bulbs.

The halogen cycle begins when an electrical current flows through the filament and heats it up to white hot to produce light.

The halogen redeposits the particles burning off the tungsten onto the filament which are then reused in the next cycle.

Incandescence results in a high lumen output and a much higher colour rendering index with the disadvantage of infrared heat.

Why Your Halogen Fittings Just Won’t Do the Job

LED Bulbs Must Be Used in Open Fixtures

You probably have a heat guard and enclosed fixtures for your halogen downlights. This is because they give off too much heat when emitting light.

Though LED bulbs produce a small amount of heat, they’re very sensitive to high temperatures, so you’ll find them installed in open fixtures.

This allows for heat dissipation which in turn will lower the risk of fires, luminous flux and colour shift.

LED Downlights Need a Heat Sink

The heat from halogen downlights goes outward, warming up the room while that of LEDs is discharged from behind the light source and into the fitting.

This heat goes into the heat sink (an aluminium surface attached to the LED) and is transferred into the air.

A heat sink requires 30cm2 per Watt consumed so a 10W bulb would need a heat sink that’s 300cm2.

Can your halogen fitting accommodate a heat sink with these dimensions? You’ll certainly have to replace all your fittings to go LED.

LED Bulbs Require a Dimmer Switch

Dimming enables you to select the perfect amount of brightness you need and also reduces the electric load on your fixture.

LEDs, unlike halogen lamps, don’t rely on voltage to dim lights, they use two methods: analogue and pulse width modulation (PWM).

Analogue dimming controls current to either brighten or dim your downlights.

In PWM, the cycle goes on and off in milliseconds, which is invisible to the human eye. If you dim your downlights to 30%, the cycle will be off for 70% of the time and on for 30%.

You can purchase dimmable LEDs even if you have a non-dimmable circuit but non-dimmable LED downlights can’t be used on a dimmable circuit without spoiling it.

Halogen dimmers are designed to dim circuit loads of 100W to 500W. Since LEDs have a lower wattage, your halogen dimmer won’t have the sensitivity to dim at low wattages.

You are bound to experience flickering and in some cases your bulbs may not even turn on if you attempt to use your standard incandescent dimmer switch.

Types of dimmers

  • A single pole dimmer is used when the on and off switch also works as the dimmer. It’s perfect for small rooms with few light sources.
  • A plug in dimmer dims table and floor lamp bulbs.
  • A multi-location dimmer dims the downlights from any room in your building.
  • A Three Way/Four Way dimmer is used when there is one only one dimmer but two or more on and off switches in your building.Three way dimmers are found in corridors and stairwells while four way dimmers can be located in large rooms with multiple doors.

LED Downlights Need a New Transformer


To maintain maximum efficiency, LEDs must have a constant DC current.

The power fluctuations of an AC power supply shortens the life cycle of LEDs, causing buzzing sounds, erratic dimming and flickering.

The high voltage from your halogen transformer will not only lead to a lower light output, your LEDs will be destroyed. The excess power will blow into your LED downlights especially if you have recurrent voltage spikes.

If your transformer connects to the circuit through pins, replace your halogen transformer with an LED driver to regulate the voltage.

It’s not a must to replace your transformer if it uses pegs unless you want the ultimate confidence in your LED system.

What Type of LED Transformer Should I Use?

  • Constant current transformer: It has a fixed current output and specifies power in milliamps (mA) and amps (A). It varies the voltage throughout the circuit but keeps the current constant. Ideal for high powered LEDs, this driver ensures that voltage fluctuations don’t lead to burn out and thermal runaway. Use a constant current transformers for illumination because it will give you better control of the light quality and brightness of your downlights.
  • Constant voltage transformer: It has a fixed voltage output of either 12V or 24V. This transformer is used in LEDs that have an inbuilt resistor to regulate current but need a stable voltage to function. They are more expensive and less efficient than constant current transformers. Use a constant voltage transformer when you don’t know your LED load or when your downlights are connected in a parallel circuit.

How Do I Pick the Right Transformer?

Select a driver with a higher current requirement than your LEDs: Your LED downlights must run at a lower current rating than your driver for a longer life span.

Determine the installation site then pick a transformer with a high IP Rating: Where do you intend to install your LED driver? If it will come into contact with stray wires, dust particles or water droplets, it should have an IP rating that is above 66.

Match the volts on your LEDs to that of your driver: This will enable you to buy a driver with the right voltage requirement

Choose a transformer with a power factor between 0.9 and 1: The more load a driver places on your electrical network, the more efficient it is.

Select a driver with dimming ability: You’ll have more control of the brightness and save on electricity.

If you use LED downlights in incompatible fixtures, it may void any warranties they have. Avoid sabotaging your LED upgrade. Contact an electrician to assess your halogen fittings and install new LEDs.