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Another advantage of the Prius is that, while both it and the compact fluorescent bulbs reduce greenhouse gases, the CF bulbs are cutting consumption of electricity, while the Prius is cutting consumption of petroleum. It's a good thing to reduce the use of domestic resources (including natural gas and coal, but little oil) that go into production of electricity, but it's even better to take a bite out of our nation's oil addiction.

On the flipside, the CF bulbs reduce "ordinary" pollution (toxic and smog-forming compounds, as opposed to non-toxic greenhouse gases) from power-generating plants compared to incandescent bulbs; however, the AT-PZEV Prius is no cleaner than the many non-hybrid PZEV vehicles (starting with the 2000 Nissan Sentra CA, years before the Prius was certified to PZEV emission standards), in terms of "ordinary" pollutants. The Honda Insight hybrid will cut even more greenhouse gases, but it will emit more "ordinary" pollutants than many "ordinary" cars. To improve on these pollutants in an automobile beyond the levels available from ordinary cars, you need a fuel other than gasoline, like natural gas (the Honda Civic GX is the cleanest internal-combustion-engine vehicle ever made, and cuts CO2 by about 25%) or electricity.

So to cut both petroleum use _and_ toxic and smog-forming emissions while you're cutting greenhouse gases, look to natural-gas vehicles, battery-electric vehicles, or plug-in hybrids.

Charles Fischer

I thought I would do my own comparison. First the cars. I drive a 2004 Ford Focus wagon (PZEV version) and average a bit over 30 MPG. When I drive my girlfriends Prius, I get about 50 MPG. At 24,000 miles a year the Prius would save me about 320 gallons (800 Focus gallons – 480 Prius gallons). In reality this is an over estimate. When we travel together with our bicycles, we always take the Focus, because the bikes fit inside the Focus. With two bikes on the roof, I would think the mileage of the two cars would be close to the same. To adjust for this I will change the miles driven from 24,000 to 20,000. This results in a savings of 266.67 gallons (666.67 – 400). So my yearly CO2 savings would be 2960 Kg. I paid about $15,000 for my Focus, and if I bought a Prius it would be about $25,000. At $3.00 per gallon, the Prius would save me about $4,800 (six years). So over the six year life time of the cars I would save about 17,760 Kg of CO2 or 3.42 Kg CO2 per $1.00.

I have 13 CF bulbs in my apartment. That is every socket that CF bulbs fit into (all but the small bulbs in the bathrooms and one other). Typically I have about four bulbs on for about seven hours each day. So at 77W for 7 hours for 4 bulbs I save about 787KWh or 1,062 Kg of CO2 each year. At Lowes a 30 watt CF bulb costs $8.98 and lasts 6000 hours. A case of 24, 100 watt bulbs costs $9.98 and lasts 750 hours each. The CF bulb puts out a little bit more light (1840 vs. 1750 lumens). So buying 3 CF bulbs will last as long as the 24 incandescents. So in up front costs the CF bulbs cost $26.94. The KWh savings over the life time of the bulbs would be (70 watts for 6000 hours * 3 bulbs) 1.260 KWh or 1,701 Kg of CO2. I pay about $0.09 per KWh, so the CF bulbs would save me about $93.44.

Another place to save a bit of CO2 is with LCD monitors replacing CRTs. I have one computer that I use about 10 hours per day. The 19 inch LCD monitor is rated at 41 watts. The 21 inch CRT it replaced was rated at 125 watts. This one replacement saves 414 Kg of CO2 per year. The difference in cost between 19 inch LCD and 21 inch CRT nothing at this point in time (ViewSonic 21 inch CRT G225fB $519, ViewSonic 19 inch LCD VP930b $479). So at 10 hours per day for 4 years I will save 1,656 Kg of CO2 and save about $110.00.

From an environmental point of view all three options are good ones. For me the Focus wagon fits my lifestyle better then the Prius, and the Prius comes closer then the Honda Civic. The Focus wagon gets as good or better mileage then the hybrid SUVs and does not pollute any more. So should I take some of the money I saved by buying the Focus and buy 32 CF bulbs to give away to the poor? That should cover the CO2 difference between my Focus and a Prius for six years of driving.


Good comparisons, Charles. However I believe an emission factor of 1.35 lb/kWh, not 1.35 kg/kWh, is closer to the national average.

Jerry Kindall

Don't forget, with the CF bulbs you're not just saving by using fewer watts -- in the summer you're saving by not having to cool the heat wasted by incandescent bulbs. In the winter I think this works out to be a wash (i.e. you pay about the same to "make up" for bulb heat as you would to run incandescent bulbs), but it's definitely an advantage in summer.


what about the difference in the color of the light. I run the circular/spiral florescents in lamps all over the house, but the light is either yellow or greenish. We bought Philips marathon bulbs this time, instead of the generics we bought last time at Home Despot, but even the Philips has a yellow glow. Who makes energy saver bulbs that actually produce a warm reddish (sunlight color) white light?


Heather, the difference in light quality is partially because of color temperature differences (incandescents are actually much warmer at 2800K v daylight at 5000K), but primarily because most cheaper CFL bulbs have a much lower CRI, or color rendering index.

The CRI is a measure of how a light source can reproduce the colors of what it's lighting. Incandescent bulbs, which basically are black body radiation is near 100.

For the best quality light, you'll want something w/ a CRI of at>80. I've started to some CFLs that claim a CRI of 91-96 recently, but haven't tried them out yet. (The Chromalux Ecolume bulbs look worth trying out. I'll be ordering some from Bulbster.com, which seems to have the best price, pretty soon).

Light Bulbs Zach

My website has a light bulbs energy savings calculator that may help out in this discussion.

Norman Fine

In cold weather the heat generated by an incandescent is not wasted. Since where I live [northern climate] heat is used to warm my house about seven months of the year this factor should be entered into the energy savings calculation. In addition the extra cost of the fluorescent is a loss of income, X dollars at 5 percent for 10 years.


Hybrid technologies have gone a long way in the past few years, and we have the oil companies to thank in its own strange way.

Harry Stone

Great blog you have, i am doing a study on this subject and i fund some great information on your site

Thank you for that

Harry Stone


According to the EIA, the average coal plant in the US produced 2.095 lbs/kWh in 1999 (http://www.eia.doe.gov/cneaf/electricity/page/co2_report/co2report.html see Table 4). So if you get 100% of your energy from coal then you'd use that number in your calculations. The national average is something like 52% coal, but you really need to look at your utility's energy mix because the numbers can vary wildly. 1.35kg/kWh seems really high for the national average based on the EIA data.

Lucy Meadows

What I really want to know is whether it makes more environmental sense to buy a new hybrid - considering both gasoline usage AND all the resources required to manufacture it- or just drive my 98 Corolla into the ground.

Somebody has to have researched this - anybody know the answer?



I wish to make a comment on the issue of saving energy (and co2 emissions) by using energy efficient light bulbs.The savings you calculate only take into account the light bulbs themselves.The estimated time of usage is also very high. Some room sin a house (e.g bedrooms) might only have a light on for 30 minutes a day. Also some rooms (bathrooms, halls, porch) use lights for numerous short periods. Energy saving bulbs are more wastefull when constantly turned on/off for short periods.Also energy saving bulbs do not operate well in cold areas, (e.g attic/outhouses,porch). Because they create heat the normal light bulbs are like mini heaters.Due to this the central heating system (when in use) has less work to do. If all light bulbs are energy efficient fluorescent ones the central heating has to provide all the heat (and use more energy itself). Perhaps a proper study should be organised to compare the different light bulbs, by using two identical houses, with identical usage patterns, (i.e. lights on for the same number of hours, heating set at the same temperature, and on for the same periods, and with each room having it's own thermostat set at the same temperature. The energy used by the two houses from their lighting, appliances,and heating system could then be added up and a true comparison could be made. I reckon the amount of energy saved by using energy efficient Light bulbs would not be as anywhere as big as the figures you quote.
P.S. items such as insulation, lagging jackets are very important to 'real' energy savings. A properly built and insulated house will 'trap' and retain the heat from 'so called' wastefull appliances.(i.e.energy inefficient fridges,cookers,washing machines, dish washers, driers, lightbullbs). Using energy saving devices in these conditions will not result in the savings calculated by using maths alone(i.e. appliance A uses x more energy per hour that appliance B , and then 'falsely' coming to the conclusion that all this extra energy is immediately waisted.) A well built and insulated house will retain the extra energy used as heat.We use lights (and many other appliances) more in the darker (and colder) months.

Greg Morgan

I'd like to point out two numbers I've found: from personal use of my Prius, over the first year, 15,900 miles, about 11,000 on Interstate conditions, the rest local surface, I used 359 gallons of gasoline--44.2 mpg; from the Federal Highway Administration, which reports the total miles driven by the reported fleet of 225 million cars and light trucks/vans/SUV's, and the gasoline used by that fleet, and calculates a fleet average of a hair under 17 mpg.
I used the density of gasoline as 6.15 lbs/gal and the C:H ratio of gasoline as 36:7 (w/w) (the resulting CO2/ gallon is about 8% lower than the 11.1 kg/ gal you use) and calculated the Prius CO2 savings as 10,800 pounds vs. an "average" car driven the same distance. The estimates for mpg figures, gasoline to CO2 constant, national fleet averages are compounded by the huge variations in CO2 per kWh electrical use across the country, so I can see how a good go at switching home lighting to florescents might fairly be equated to driving a Prius. Do both, win two rounds for good ol' Mother Earth. And hope for the speedy arrival of the H2 fuel cell private conveyance, and the multi-gigawatt photovoltaic farm.

Hybrid Authority

I want a hybrid that uses no gas. I know it can be done, but they can't sell gas then and who knows what will happen then. I call it my perpetual motion hybrid vehicle. Anyone want to give it a whirl?


It's good to hear BP & GM talk about alternative fuels, but 50 years to implement is too long.


Perhaps this link will spark more attention:


It is GM's electric concept car the Chevy Volt. If more people begin to demand alternative fuel cars, we should be able to speed the rate at which the technology is developed.

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