Downlight transformers: The good, the bad, and the very inefficient

Transformers

Not all halogen downlight transformers are created equal when using them with retrofit LED globes. Alfred Howell explains how the wrong transformers can be costing you money.

With the retrofitting of LED downlight bulbs to MR16 halogen fittings, households have seen great efficiency gains and cost savings.
However, if you change your bulbs to low-power LEDs but don’t check the transformers, you may be wasting energy. Many of the older downlight fittings use ferromagnetic (iron core) transformers. While simple, they are inefficient compared to modern electronic replacements. To determine the extent of losses in these transformers I performed some simple testing.

Testing and results
I tested a typical ferromagnetic transformer alongside an Osram Redback electronic transformer. Both transformers were tested, with and without a Brightgreen DR700 retrofit LED globe. A Power-Mate Lite energy meter was used to measure power draw.


Type No globe, or globe blown 10.5W globe fitted

Ferromagnetic 5.34W 18.23W

Electronic 0.38W 13.13W

Savings 4.96W 5.10W

Table 1. Energy consumption of electronic versus ferromagnetic transformers,
with and without a load (globe) fitted.

 

As can be seen in Table 1, the electronic transformer performs well with or without the globe. While it seems a bit pointless to test a transformer without a globe fitted, it’s actually a good indicator of the efficiency, or otherwise, of each transformer. Compare the electronic transformer’s 0.38 W draw without a globe with the ferromagnetic transformer’s draw of an extra five watts. Indeed, the ferromagnetic transformer uses an extra five watts more than the electronic transformer with or without the globe’s load.

While that doesn’t sound like much, it’s not uncommon to find 20 or more downlights in a home. With all 20 lights on, that would be an extra 100 watts burning a hole in your wallet—or 0.5 kWh if they’re on five hours a day.

Solutions and options
To reduce this energy use, the cheapest option is to swap the ferromagnetic transformers for electronic ones when you retrofit. They are low cost, usually under $15, and available from electrical wholesalers and lighting stores. Alternatively, you could upgrade the halogen fittings to dedicated LED downlight fittings with an incorporated driver.

An even better option is to remove the downlights altogether in places where suitable. Downlights compromise ceiling insulation as they must be uninsulated to prevent the fitting from overheating. Also, many downlights, even LED ones, have a fairly narrow beam angle and so tend to produce pools of light. To get high ambient lighting levels requires a greater total wattage from downlights or a light fitting with a wider dispersion, such as an oyster fitting.

It’s clear that changing the globe as part of an energy saving makeover is only part of the solution. For maximum efficiency and results, the whole lighting system, and how the system is used, needs to be evaluated. This includes behavioural changes such as turning lights off when not in use. With a bit of effort, you will be amazed at the savings that can be realised.

Alfred Howell has years of experience managing complex machines, which he reckons puts him in a terrific position to understand how we can work as part of this complex machine we call Earth.

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