Heating & energy
It can cost up to twice as much to heat an open-plan room that has downlights as one with a single-bulb ceiling light.
Most recessed downlights have large ventilation air-gaps that keep the light bulb (and your house) cool, by venting warm air from your living areas into the roof space. "Little chimneys” - as downlights are known in energy-efficiency circles - could be robbing you blind.
A room with multiple recessed downlights
A smooth ceiling with recessed downlights has been “the look” for a decade or two. It may look nice; but these fittings waste energy.
First off, there’s the number of downlights you need. Because recessed fittings cast a narrow beam of light, you could need up to eight fittings in a lounge where a single ceiling dome and a couple of wall lights would do the same job. And more lights mean you use more electricity.
But the biggest problem with downlights is the loss of warm air from the living area into the roof space. That’s because each recessed downlight has a ventilation gap around it to stop it overheating, and this allows warm air to escape.
These gaps on windy days can also bring contaminated dust and dirt from your roof space into your home – and they can vent the moist air from your bathroom into the roof space, which reduces the effectiveness of your ceiling insulation.
About our test
What we tested
An R-rated fitting
We tested a range of different types of downlight fittings to see how much warm air was lost from the room. We didn’t test their light output, or all the downlight fittings on the market.
So what the test shows is how different types of downlight fittings – and the bulbs in them – affect the amount of heating required to keep a room warm.
What the ratings mean
How much hot air escapes into your roof space depends on the downlight fitting’s design and its rating. We tested fittings with RS, CS and CA ratings.
A C-rated fitting
The (R) and (C) ratings refer to the size of the vent to the roof space:
- (R) Restricted. The area of the vent to the roof space is between 5 and 15 percent of the area of the hole cut in the ceiling.
- (C) Closed. This isn’t “closed” in the sense that most of us would think – there’s still a vent but its area is no more than 5 percent of the area of the hole cut in the ceiling.
The (S) and (A) ratings are about the insulation-clearance:
- (S) Specified. The insulation-clearance distance is specified.
- (A) Abutted. The insulation can be abutted up to the fitting but can’t cover it.
We built a heated test-room inside another temperature-controlled room – that is, one room inside the other. The heated (inner) test room was insulated as you’d insulate a house. The temperature of the outer room was controlled to 9ºC.
The 3 different non-halogen bulbs used.
The overall set-up simulated a heated lounge with a cool roof space. We then measured the total energy (lights and heating) required to keep the inner room heated to 20ºC.
We then tested several examples of three common downlight fittings with different bulbs:
- R-rated fittings were tested with standard incandescent (GLS) bulbs, then incandescent reflector (R80) bulbs and finally CFLs.
- C-rated fittings were tested with the same three types of bulb.
- CS-rated halogen fittings were tested as supplied and then again when fitted with the manufacturer's CA kit. In both cases we used standard halogen MR16 reflector bulbs.
We also looked at how much difference there was if we had more than one recessed fitting in the ceiling. To do this, we ran some tests with a single fitting and then with four fittings.
Guide to the table
Our test was carried out at an independent laboratory in New Zealand and funded by the Electricity Commission. See About our test for details of what the downlight fitting ratings mean.
Extra room-heating required is the extra energy (lighting and heating) required to keep the test room at 20°C when downlights are used. It’s expressed as a percentage of the energy required when the room is fitted with a single bulb-holder and a 15W CFL bulb.
What we found
CS-rated halogen fitting
More fittings increases the heat loss – although doubling the number of fittings doesn’t double the loss.
There was some reduction in heat loss when RS- or CS-rated fittings were replaced with CA fittings (see About our test for what the ratings mean). This happened whatever bulb was used.
See the “Extra room-heating required” column in our test results table – it shows how much extra heat was required to keep the room at 20°C, so you can also see how the heat loss varies with different fittings and bulbs.
CA kit fitted on the halogen light
Swapping a standard incandescent GLS bulb with an R80 reflector bulb in the same fitting also reduced heat loss. We suspect there are two reasons for this.
First, reflector bulbs are larger in diameter than the standard bulbs and this means they “fill up” the fitting better, reducing the air gap around the bulb. Second, these bulbs also reflect light and heat downwards – this would result in the fitting running cooler, which in turn would reduce convection currents of warm air through the fitting.
Swapping to a CFL bulb reduced the energy loss even further. But we have reservations about fitting CFLs into recessed fittings not designed for them. Good CFLs produce at least as much light as their equivalent incandescents, but when fitted to older recessed fittings they often “stick out” a bit.
This means the reflector doesn’t work properly, the light bounces around inside the fitting and the resulting light output is not as good as it should be.
In halogen fittings, the heat loss from the halogens decreased a little when the optional CA kits were used.
We did calculations for a typical 5m x 4m living room with an insulated ceiling, uninsulated walls and a wooden floor. Our "What size heatpump" calculator says it would take 3kW to heat the room.
From our test results we estimate it would take 5.7kW to heat the room if it had six R-rated downlights in the ceiling.
Replacing those six R-rated downlights with CFL-specific CA models would reduce the heating required to 3.75kW. The fittings would pay for themselves in less than a year (if the room was heated with electric heaters) or in just over two years (if using a heat-pump).
These calculations include the cost of the new fittings ($26.55 each) and $300 for an electrician to fit them.
Don't cover downlights
Downlights might be robbing you blind - but if you cover them over - you could burn down the house.
Our test has resulted in some discussion suggesting that covering downlights would solve their heat loss problem. No, no, no and no.
The ventilation gaps around downlights allow warm air to escape from your living area into the ceiling space.
That's bad … but these gaps are designed to stop the fitting from overheating. Covering downlights with insulation – or anything else – will stop that airflow, overheat the fitting and could cause a fire.
That’s much worse than the heat you lose. It's happened in Australia where house fires have been attributed to covering downlights with insulation material.
We think it’s cost-effective to replace old downlights with new CA- rated fittings designed specifically for CFLs.
- Recessed downlights waste energy by sucking warm air from your living area into the roof space.
- Downlight fittings designed for non-dimmable CFLs are available. These give good light and minimise heat loss.
- If changing your fittings is not an option, replace standard incandescent bulbs with reflector bulbs (incandescent or CFL) – they reduce heat loss.
- If you’re renovating, don’t specify downlights. Look for other lighting options that don't require holes in the ceiling.
Insulation and downlights
Adding extra ceiling insulation can improve the energy efficiency of your home. But be careful if you have downlights.
Any insulation must be installed with the correct clearance from the lights and must never be placed over the downlight fittings. Covering the fittings stops air from rising through the fitting and is likely to cause overheating – or even a fire (see Don't cover downlights).
In Australia, house fires have been attributed to covering downlight fittings with insulation.
- RightLight website: www.rightlight.govt.nz
Report by Bill Whitley.