When it comes to homes, lighting has become a luxury of the modern age. Architects have steadily grown to gorge themselves on light fixtures. Without a doubt, nice lighting can certainly look cool, but it is easy to go overboard. Light a circulation path here, throw in some accents there, before we know it we end up with over 62 lights in the average house. For residential buildings, exterior lighting ranks up there in convenience of questionable necessity like automatic blackout shades or heated towel racks. Beyond just the materials and energy used to make and install lighting, its presence carries a lasting toll on energy use.

New figures recently released by the Energy Information Administration (EIA) point to residential buildings as the least efficient of any type in their lighting use. Despite the number of technological improvements coupled with the growing awareness and experience in greener building, overall efficiency in residential space has hardly improved at all over the past decade.

According to the Department of Energy, America has an estimated 8.2 billion fixtures actively producing light—about a 17% increase from 2001.  Together they consumed an estimated 700 terawatt hours of electricity. How much is that? (An average sized 650 MW coal plant will produce about 5.7 TWh a year running at full capacity, 24 hours a day.) It's a lot.

The DOE data analyzed by the EIA on the lighting load of our nation's buildings over the past decade is… illuminating? Our homes account for 71% of all of the fixtures installed in the country, but they account for only 8% of the lumens produced. The study broke lighting usage into four categories: commercial, industrial, outdoor and residential with each comprising a meaningful piece of the total amount of electrons we produce for illumination. While the first three have steadily improved to reach admirable levels, the lighting used in our homes cemented them in dead last.

Over the past ten years, residential lighting has not only been the laggard in efficiency, but it has also shown little improvement. The figures are calibrated in the metric of efficacy which is the amount of lumens (light) per watt (power). The more light we can produce for less power consumed pushes efficiency upward. Lighting for commercial, industrial and outdoor applications have reached comparable average efficacy levels, all within 10% of each other. Residential spaces drag behind with an average efficacy of only 19 lumens/watt, around 27% of commerical's very distance 3^rd place finish at 70 lumens/watt. Worse yet, the past ten years have not shown drastic improvement for home lighting, increasing just 2 lumens/watt since 2001.

The source of the relative deficiency is not a mystery: incandescent bulbs. A growing portion of the population is aware that standard incandescent bulbs use most of their operational energy to produce heat rather than light, making them staggeringly inefficient compared to the other options on the market today. Unsurprisingly, our homes use the largest number of incandescent bulbs of any category, comprising 62% of bulbs and 78% of lighting energy use. Figures like this help explain why the average energy use of our homes have remained constant for nearly the past 40 years. According to the DOE, lighting comprises about 6% of our energy at home.

What About Phasing out Incandescents?

Contrary to the best efforts of Congressional Republicans, the phasing out of traditional incandescent bulbs has formally begun with the highest wattages being the first to go by the end of 2012. With the estimated 3.7 billion incandescent lamps in service, it will take a while for them to evolve, but at least we have reached the starting line. The study seems to think that the data should be notably different 10 years from now when a boarder switch to CFL and, more importantly, LED fixtures will have a material impact on the amount of power we use at home.

How Much Power Does it Really Save Us?

Critics of the law requiring increased efficiencies from incandescent bulbs often poke at the question of how much energy will we really be saving. The numbers point out that incandescents are responsible for 156 TWh of electricity annually. The vast majority of this (86.5%) is in our homes. According to the DOE, the standard incandescent has an average efficacy of about 14 lumens per watt, so a 60-watt bulb produces about 840 lumens of light. Conversely, a CFL and LED produce the same amount of light using around 14 watts and 11 watts respectively. A migration to the level of CFLs would be saving about 119 TWh of electricity a year, or about 22 coal power plants.

For designers it is important to remember that the most efficient fixture is the one you don't use at all, which can be paired with removing spaces in homes that we don't really need like formal living and dining rooms. Does that hallway really need recessed halogen fixtures every 3 feet on center? Maybe we are past the exterior, color-changing up-lighting? Using elements like skylights and solar tubes can bring more light deeper into a space to negate daytime use of artificial illumination while things like light shelves can horizontally stretch window light into interior space. As a species that spends about 90% of our time indoors, the power-consuming technologies we use play a vital role in our evolution towards a more sustainable society.

Image Credits: eia.gov , besthomy.info