Published 22 May 2012

Study of effectiveness of recessed downlights in an open plan lounge

An earlier article on LED globes included my comment that recessed downlights are a dumb idea for wide area illumination. This is a brief study to obtain a view on the scale of any issues with the levels of light, the cost of running an area fitted with incandescent reflector lamps and what might be done to improve the lighting. It should be emphasised that I am not a lighting consultant but I expect the broad scale of the results here will be fairly representative of the issues of lighting an open plan lounge/dining/kitchen space.

Lamps and fittings in use

The house is reasonably typical of the spec type townhouses built by building companies in the early 1990's. White painted ceilings, 2.4 metre stud height, painted walls and carpeted floor. Open plan lounge/dining and kitchen area. No detailed lighting plan that would be made by an consultant; rather more likely done by the in house designer or even left up to the sparky. The lamps are the PAR 80 (equivalent to PAR 25 in the U.S) with ES 27mm base. A couple of photos are below. First simply shows a lamp and fitting in situ; the second shows the fitting removed from the ceiling to extract a lamp which base had parted company with the bulb.

downlight fitting

The fitting is basic. It breaks the insulation of the room space by leaving around 6mm space between the housing and the lamp. There is no provision for a cage to keep the ceiling insulation away, however, the use of reflector lamps means that most of the heat does get directed down and that there is no risk of overheating. Having said that, I would not simply retrofit any other kind of lamp into these fittings.

Cost of running these incandescents

There are six downlights in the whole open plan area; three in the lounge/dining part and three in the kitchen. A floor plan is shown a bit further down. Five of the lamps are 100 watts, but one turned out to be 75 watts, so we have a total of 575 watts of lighting power in the ceiling over the entire area.

In winter, the lights are all on for 6 hours per day. In summer, around three hours.
So, using the effective rate charged around here, which totals 28.6 cents per unit, these lights cost NZ$270 per year to run.
This represents about 10% of the annual power bill.

575 watts seems to me to be an almost obscene amount of power to use for lighting this space, so just how well does it do the job?

Illumination readings

Firstly, one downlight by itself is measured with the light meter. I used a working plane of 750mm above the floor. This is a common height used in the industry for illuminance measurements. Coincidentally the dining table is exactly this height as well. A graphic of illuminance (in lux) versus distance out from the line of the lamp is below. Also shown is a plot of values which is another illustration of the same thing. These are averages of several measurements:

Lux graphicLux graphic

Directly below, we get 340 lux. At 350mm away, this has dropped to 270 lux. By half a metre, we are at 185 lux, at 1 metre the levels are 80 lux and by 1.5m, only 35 lux. These downlights produce a 'pool' of light about 700mm diameter and the light reduces rapidly the further out you go. Given that authorities regard that between 300 lux and 800 lux is needed for doing fine tasks and for reading, it is clear that we get only the minimum light suitable for reading within a circle of 700mm diameter around the lamp. I suppose this should not be too surprising since these lamps are 'spot' lamps and the housing will further concentrate the light into a beam, since the lamp itself is actually recessed about 1cm into the housing.

If one wanted more even illumination over an area, using these lamps, they would need to be spaced no more than 1.5 metres apart. Doing that will mean many more lamps were required and an even more horrendous power consumption. There is a minor mitigation and that is reflections. With these lamps, there is virtually no scatter and help from the ceiling, but reflection from walls and objects do help 'scatter' the light around a little. However, scatter does not make for even illumination for reading and tasks over the area. The 'pools' of light and indirect scatter does make for reasonable 'ambience' lighting and that is why they are all left on most of the evening.

Next a complete map of the area is made. See the plan below:

Floor plan

This plan shows the kitchen area to the left and lounge on right. The yellow circles are the lights and they are numbered in the green triangles. The light readings are in red. Readings are all taken 750mm above the floor, except in the kitchen where they are taken on the working surfaces, which are 900mm above floor and 1130mm for the breakfast bar below lamp 4. The reading under lamp 6, near the pantry is again at the 750mm level. This lamp is the one 75 watter in the space. All ceiling lights are ON for this map.

The kitchen area is 10.5 square metres and the overall lounge area is about 34.5 square metres, omitting the stairwell and short hall to the upstairs bathroom. Any readers in the U.S might want to multiply by 10 to get square feet.

The readings obtained may seem a little inconsistent but bear in mind that they depend on a number of factors.

Looking at each area in turn:

Kitchen

This area and the working surfaces are reasonably well lit. Food preparation, dishwashing and cooking activities are no problem. There is a light in the extractor over the cooktop, which improves lighting there when needed. There remains the question of whether the power consumption for lighting the kitchen could be reduced.

Lounge

The lounge area has three lamps which is the same number as the kitchen area. The difference is that the lounge is over three times the area of the kitchen. There is some assistance into the lounge, particularly over the dining table, from lamp no.4 above the breakfast bar. The centre part of the lounge is poorly lit, as shown by all the low readings around both the 3-seater couch and the single seater at the head of the dining table. Reading is not easy in these parts of the lounge and there is a reading lamp (not shown) next to the single seater. In fact, the only parts of the lounge where it is possible to read without strain using just the overheads is at the 2-seater couch and on the dining table. Lamps 1 and 3 are overlapping reasonably well near the 2-seater, although light intensity would still be called marginal for reading by the experts in the industry.

Improving things

If it was necessary to improve the area lighting for the lounge, one quick fix that comes to mind is to add three more downlights. One would be equidistant between lamps 2 and 3, while the other two would complete another row down from lamp 1.
Of course, that increases power consumption by a further 300 watts. With six lamps now in the lounge, each could conceivably be down-powered to 75 watts because of the improved overlap. That still makes 450W in the lounge plus the 275W in the kitchen; being 725 watts in all, and more power stations would be needed.

All of which says that spot downlights are useless at lighting an area, at least to a satisfactory level for reading and doing other tasks, unless you park right underneath them. Someone is bound to point out that reading these days is done using self-illuminating reading devices, but I still need to turn actual paper pages at times.

Back in the good old days

Don't you just hate it when someone keeps harking back to the good ol' days? Well I won't spend long here but believe me, there is plenty to learn from the past, especially from past mistakes! This bit isn't a mistake, but in the fifties and sixties, before fashion and trends intruded, an area like the above would have been lit by two 150 watt bulbs in the lounge and one 100 watt in the kitchen. You will remember the coolie-hats if you have been around sufficiently long. These were attached to a surface mounted light socket on the ceiling and acted as a low gain reflector. The usual plastic cheapos were ugly but you could get more appealing versions. cooliehatThe bulbs directed light all around and some would have even been reflected from the white ceiling. My thinking is that all-round illumination would have been better than the current installation of downlights, although there wouldn't be hot-spots directly under the lamps. Sometimes, lights were suspended from the ceiling including some simple lampshade. These probably gave good area coverage especially from indirect light scattering from the ceiling, but suspended lights are a bit intrusive when the ceiling height is only 2.4 metres. 400 watts back then versus 575 watts now with a poorer result. That must be what they call progress.smiley

Better options

OK, things are never quite that simple. Sometimes you want less light, although that could be solved with a dimmer. Some might want to watch TV possibly while someone else wants to read or do a Sudoku. More flexible lighting options are the way to go and of course we want to reduce that prodigious power consumption down to a respectable amount.

CFL's and LED's

More energy efficient lighting is available, but you will need to customise the solution for your needs. I don't recommend just popping a CFL or a LED bulb into an old downlight fitting that was built for incandescent reflector bulbs. First, you will get less light than now and worse, you can create a fire hazard in the ceiling space. Both CFL's and LED's are better fitted into properly designed fittings, but best of all, especially for LED's is to buy integrated lights. Buying new fittings (or lights) will cost money and it is likely the payback period will be several years. Unfortunately, even organisations promoting energy saving lamps don't mention the cost of new fittings. This makes the sums less attractive, although if you are planning to stay in the same house for a while, the exercise will pay off.

I don't intend to offer products or solutions here. Good quality CFL's are OK now. My main remaining misgiving about CFL's is the start-up time. To replace a 100 watt incandescent really needs a 26 watt CFL although some say 20 watts is enough. Perhaps in a good fitting, it is near enough. LED's are quite an attractive proposition except the better quality ones are still very expensive. At the present time, you can get good quality integrated 18 watt LED ceiling lights that give about the same light as a 75 watt incandescent, but these are over US$200 apiece. There are some less expensive examples in catalogues, however the devil is in the details. Often the specs are inflated, the lifetime exaggerated and the presumed benefits or savings never will arise.

Instead of recessed downlights, my preference would be for a surface mount, low profile LED ceiling light perhaps 300-400mm diameter with a frosted glass cover. The low profile would not be too intrusive in a 2.4m ceiling room and being surface mount will help to avoid the spotlight effect. No heat will escape into the ceiling space. The dimming variety would also be useful. Couple a number of these in the room with some ambience uplighting and I suggest a good compromise is met.

If you are building, then a proper lighting design is in order. LED's will be the choice. In fact, there is then no need to have 230V AC cabling for lights at all. Run all lighting circuits as 12V or 24V dc. Better efficiency and no fire or personnel hazards.

Links

Power quality of small appliances (Related article)
Tests of Viribright and PhilipsLED globes
Axino-Tech HOME
Brightgreen Premium LED lighting
EarthLED Home
eco bulb Home

From:

Comment

There are no comments yet

Make a comment using the form on the contact page