What you actually save by getting rid of halogen downlights

Do the sum in watts, not dollars

A typical halogen downlight draws about 55W. The LED that replaces it draws about 10W and puts out as much usable light.

Twenty of them is the difference between 1,100W and 200W, so you are saving 900W whenever the lights are on. Run them four hours a night and that is 3.6kWh a day, or a bit over 1,300kWh a year, from one afternoon's work.

Multiply that by whatever you are paying per kilowatt hour on your current bill and you have your own number, which is more use than anybody else's. Count the downlights in your house first. Most people are surprised, and the ones with the most to gain are the most surprised.

They last long enough that you stop thinking about them

An LED lamp outlasts anything that came before it by a wide margin. Rated life is usually quoted between 25,000 and 50,000 hours, so at eight hours a day in a workplace that is somewhere between eight and seventeen years. Take the lower end in a hot ceiling in the tropics, because heat is what shortens them.

In a commercial building that is the larger saving and it never shows up on the power bill. It is the ladder, the labour and the after-hours access that stop being an annual line item.

The heat, which is the real argument

A halogen downlight runs hot enough to scorch what it touches. Surface temperatures well above 200°C are routinely measured on them, and the fitting is hot too. An LED runs far cooler, cool enough that the argument below stops applying. You can feel the difference standing under one.

All that heat sits in your ceiling space, next to insulation, next to cabling, next to whatever the last renovation left up there. Insulation pushed hard against a fitting is the classic version, which is why the wiring rules set clearances around them, and anything that touches a lamp can scorch. A burnt cable is a short circuit and a fire. It is the part of the argument people are most often surprised by.

There is a second cost to all that heat. Every one of those lamps is a small heater in the ceiling, and in this climate the cooling then works harder and longer to remove the heat your lighting has just added. Getting rid of halogen lowers the cooling load as well as the lighting load.

Two things people do not expect

• Nothing nasty in them. Fluorescent tubes and compact fluorescent lamps contain mercury, which is why they are not supposed to go in a household bin. Halogen does not and neither does LED, but an LED lamp is still electronics, so it belongs at a collection point, not in the rubbish.
• They are gentler on what they light. Fading is caused by ultraviolet and by visible light rather than by the heat of the lamp, and LEDs put out very little ultraviolet, so they are kinder to artwork and fabric than the lamps they replace. In some houses that is the deciding factor on its own.

Is it worth it?

There is an outlay to replace a houseful of halogens. But the payback period is short, and it shortens with every increase in the price of electricity and every improvement in the lamps.

The honest answer for most houses in the Douglas Shire is that the power saving pays for it eventually and the heat is why you should not wait for eventually.