Heat and Light

July 30th, 2007

Andrew K. Gabriel ’76 responds to “Attention, Wal-Mart Shoppers” by arguing that energy gained from replacing ordinary incandescent lights with fluorescent bulbs is “largely illusory” because the heat given off by incandescent lights is not wasted but rather helps to heat buildings.

This reasoning is flawed. The key point missing in Gabriel’s analysis is that heating buildings with electricity is a very inefficient use of precious energy. This is because in most countries, including the United States, electricity is almost entirely produced by combustion of such fossil fuels as coal and natural gas. The efficiency of converting that heat into delivered electricity is something like 30 percent—in other words, about 70 percent of the energy either goes up cooling towers and smokestacks as wasted heat or radiates out from transmission lines.

Heating buildings with electricity is inefficient and expensive. Burning fossil fuels in furnaces is a better way to go, because most of the heat so produced is available for heating. An even better approach would be to cogenerate electricity from the heat, something that is now being explored even for individual buildings. (Brown cogenerates some electricity at its campus steam plant, for example.) The least wasteful option of all is to construct or retrofit buildings so that they require very little heating or cooling.

If the United States were like France and generated most of its electricity from nuclear power plants, Gabriel’s argument might have merit. Unfortunately, coal is the most important source of electricity in the United States, and coal produces more carbon dioxide per unit of energy than almost any other source. Fewer fossil fuels are consumed and less carbon dioxide is dumped into the atmosphere when incandescent lights are replaced with fluorescent lights and high-quality electricity is not wastefully converted back into heat.

Brad Marston


The author is a professor of physics.

Thanks very much for the excellent article on the benefits and trade-offs of compact fluorescent lightbulbs (CFLs). Some secondary ambient heating benefit is lost by using CFLs, as Andrew Gabriel ’76 asserts, but this certainly does not render the benefits of CFLs “largely illusory” or the net effect on overall building energy consumption “almost nil.”

Ambient heat from lighting or electrical-resistance heaters can be replaced much more efficiently by the typical central heating system, which is designed for the purpose. A simple example is the basic electric heat pump, which provides many times more useful ambient heat than the power it consumes. So the reduced energy of CFLs translates almost completely to reduced overall consumption.

The larger environmental systems view is even more telling. Electricity is generated largely from fossil fuels and so is limited to a thermal (Carnot) efficiency of about 35 percent. This means that ambient heat provided by lighting or simple electric heaters requires about triple the fuel input (and produces triple the global warming emissions) than the heat produced directly in a traditional on-site heating plant. Using such hard-won electrical energy for ambient heating, even indirectly through lighting, gives new meaning to the word waste.

The bottom line is that reducing electricity use almost always has substantial benefit, including (and perhaps especially) when it affects ambient heating and cooling needs. Buy those CFLs!

David A. Dickinson ’78

Titusville, N.J.


It was somewhat surprising to see the BAM endorsing a tie-in with Wal-Mart (“Attention, Wal-Mart Shoppers,” March/April 2007), especially considering the company’s somewhat controversial marketing and hiring practices.

Beyond that, however, the analysis of home lighting by Associate Professor of Environmental Studies Steven Hamburg is flawed. The life of an incandescent light bulb can be just as long as that of a fluorescent. I have seven conventional bulbs in my home, each of which has been providing light since the house was built twenty-five years ago. An eighth bulb, which burns outdoors for hours every night finally failed after twenty years.

A long-life bulb simply requires a larger and longer tungsten filament, which you pay only a little more for. Adding iodine to transport vaporized tungsten back onto the filament gives the bulb an essentially infinite life. To compare fluorescents to the lowest-grade conventional bulbs selling for “four for a dollar” is specious.

Considering that tubular fluorescents already provide nearly all the lighting in stores, factories, businesses, and warehouses, surely the greater part of lighting wattage is already fluorescent. To impose restrictions and regulations on the remaining seems frivolous when considering the mercury recovery problem with compact bulbs, especially in small communities.

L.M. Foster ’47 PhD

Corvallis, Ore.


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July / August 2007