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Energy Use of a 100-Watt Light Bulb per Year by Source

Visitors At The Hay Festival 2011

Lighting “consumes about 19% of the world’s electric power, more than all nuclear and hydroelectric plants can produce together (which is about 15% in total),” according to Grant Feller of the World Economic Forum. With significant future projected power demand and over a billion people without proper access to electricity (see Breaking Energy ‘energy poverty’ coverage here, here and here), major power generation investment will be required to liberate people from darkness and ultimately increase the untapped productivity of a swath of the population in respective developing countries. A regional UNESCO report on “energy equity and environmental security” explains further:

“Without access to a dependable and affordable supply of energy, people would struggle to meet basic and essential needs fundamental to health and wellbeing such as heating, lighting, cooking and hygiene. In addition, the operation of many essential medical devices depends crucially upon energy use, which is also needed for the refrigerated storage of food and vaccines.”

As a consequence, power grids will have to be expanded, technologically upgraded, or built up in an economically viable as well as carbon-friendly way – with future demand growth being a fundamental consideration in the process. In developed countries, it is common knowledge that switching off lights is beneficial. Turning a light off for even a short period of time will save more energy than is actually needed to turn the same light on again. Now, how much electric power is required to keep a single traditional light bulb lit for a year – 24 hours a day? The following interesting graphic shows the energy use of a 100 W light bulb per year differentiated by source:

roman light bulb

Source: GOOD (magazine) via World Economic Forum (Twitter); click here to enlarge graphic.

Specifically, the graphic illustrates that 714 pounds of coal compared to 143 pounds of natural gas are needed to keep a single light bulb lit for a year. On the renewable side of the equation, over eight full days of sunlight hitting an area of 100 square meters covered with solar panels would be required to do the same job, while only two hours and 20 minutes of a 1.5 MW turbine spinning in the wind at 25 per cent capacity would be required. In this respect, Energy Star – a US EPA voluntary program – suggests that “if every American home replaced just one light bulb with a light bulb that’s earned the ENERGY STAR rating, we would save enough energy to light 3 million homes for a year, save about $680 million in annual energy costs, and prevent 9 billion pounds of greenhouse gas emissions per year, equivalent to those from about 800,000 cars.”

Wind power in particular appears to have advantages. From a cost perspective, wind power generation reduces the economic exposure to fossil fuel price volatility, which may justify the – in comparison to other power generation options – significantly higher upfront investment costs while operating the turbines at a lower capacity rate; i.e. operating them for a relatively low number of hours per day. Moreover, the capacity rate for offshore wind tends to be higher than for onshore wind. Therefore, in order to determine whether wind energy can be a viable option for a certain region to improve or create new access to electricity depends solely on initial costs. Fossil fuel generators, on the other hand, have limited options for optimizing cost structure. A power generator with a fleet of fossil fuel-fired plants is beholden to fuel price variability and can only limit total fuel costs by switching to cheaper fuels as markets fluctuate. Obviously, every solution has to be tailored to the specific conditions on the ground.

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Clayton Handleman's picture
Clayton Handleman on October 5, 2014

LED bulbs have cut energy consumption by a factor of 8 compared to “traditional” light bulbs.  In addition to reducing lighting costs this reduces air conditioning costs due to reduced heating.  LED efficiencies are expected to double in the foreseable future.  This article has links to a number of quantitative sources. 

Solar prices have come down dramatically as have Li-ion battery prices.  Low solar prices combined with lower battery prices and highly efficient light bulbs are a game changer for rural impoverished peoples.  For a fraction of the cost only a few short years ago, the 1 B people with no electricity now can get electric lighting without waiting for the grid to find them.  One oft unmentioned benefit of Li-ion, for this application, is the benefit of weight reduction.  Many rural villages transport goods on foot.  Lead acid batteries can be prohibatively heavy.  Li-Ion batteries have a much higher energy density, lowering yet another barrier.

It is also worth pointing out that according to EIA, 12% of US electricity consumption is for lighting.  Currently much lighting in the US is incandescent and older flourescent.  These are being phased out as the cost of LED lighting comes down.  I would love to see a good analysis piece done on this.  However, consider that the chart I linked to above, indicates considerable headroom left for LED efficiency improvements roughly doubling LED efficiency by 2025.  Even if we were 100% LED today,  That still puts us as 6% reduction in electricity consumption.  We are about 15% towards Obama’s 30% reduction target.  LED lighting appears poised to get us another 5%.  That leaves only 10%, and 15 years to get there.  Renewables alone can easily attain this.  If natural gas is also taken into account it is clear that the target is a lowball and easy to hit, likely even with very little new policy initiatives.

Robert Hargraves's picture
Robert Hargraves on October 9, 2014

The full-time 100-watt light bulb gives a convenient reference. Providing 100 watts of electricity won’t solve the energy poverty problem, even substituting LEDs for incandescent light bulbs (which is a good idea in any case). US consumption averages 1683 watts per capita. My own recommended miniumum for developing nations is 228 watts. Here are the averages for a few countries:

US 1683 watts

Canada 1871

EU 688

India 90

China 447

Norway 2603

Germany 861


Australia 1114

To solve this we need clean, safe, reliable, abundant energy cheaper than coal.

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