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------------------------------------------------ How many pounds of carbon dioxide would you prevent from entering the atmosphere in one year if you replaced a 100-watt light bulb with a CFL bulb that uses 12 watts, assuming the fixture is on for 4 hours per day?

You would save approximately 118.20 pounds of carbon dioxide per year by replacing a 100-watt incandescent bulb with a 12-watt CFL running 4 hours per day.

Explanation:

The question is asking for the amount of carbon dioxide savings by replacing a 100-watt incandescent light bulb with a 12-watt compact fluorescent lamp (CFL) that is running for 4 hours a day over a year.

First, we need to calculate the total energy savings in kilowatt-hours (kWh). Since a kilowatt is 1000 watts, we'll use the formula:

Energy savings = (Power of incandescent bulb − Power of CFL) * Time (in hours) / 1000.

For the incandescent bulb: 100 watts * 4 hours/day * 365 days/year / 1000 = 146 kWh/year.

For the CFL: 12 watts * 4 hours/day * 365 days/year / 1000 = 17.52 kWh/year.

The savings in energy would therefore be 146 kWh/year − 17.52 kWh/year = 128.48 kWh/year.

To convert the energy savings to pounds of carbon dioxide (CO2) prevented, we use the average emissions factor for the U.S. electric grid which is approximately 0.92 pounds of CO2/kWh (this number can vary based on the source of the electricity).

Total CO2 savings = 128.48 kWh/year * 0.92 lb CO2/kWh.

This results in around 118.20 pounds of CO2 savings per year.