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Name: __________________________ Section: ____ Date: ________________ LAB ACTIVITY: Chapter 20 – Sustainable Energy Choosing a Light Bulb: The following table provides information on two types of light bulbs available at a local store. Type of bulb Estimated lifetime (hours) Cost per bulb ($) 75 W incandescent . W compact fluorescent 7,.00 Assume that (i) each bulb lasts exactly its estimated lifetime. (ii) each bulb provides the same amount of usable light. (iii) the cost of electricity is $0.10 per kilowatt-hour. (a) Calculate the total lifetime cost for using each type of bulb. (b) Calculate the total cost of using the incandescent bulb and of using the compact fluorescent bulb for 7500 hours (the lifetime of the compact fluorescent bulb). (c) Most electricity in the United States is generated by fossil fuel–burning power plants that produce atmospheric pollution. Given that knowledge, explain which type of light bulb has the smaller ecological footprint.
The decision between using incandescent and compact fluorescent light bulbs involves analyzing their economic costs and environmental impacts. In this activity, we examine the total lifetime costs of each bulb type, their costs over a specific period, and their ecological footprints, considering the energy sources involved in electricity generation.
Calculating Total Lifetime Cost for Each Bulb
Assuming each bulb lasts exactly its estimated lifetime and provides equivalent light, the total lifetime cost consists of the initial purchase price plus the cost of electricity used during its lifetime.
Unfortunately, the exact cost per bulb for the incandescent and CFL bulbs is not provided clearly in the table. For the purpose of this analysis, let us assume the incandescent bulb costs $1.00 and the compact fluorescent bulb costs $7.00, aligning with typical market prices. (If actual prices differ, substitute the correct values in the calculations.)
Given these assumptions, the total lifetime cost for each bulb is calculated as follows:
- Incandescent Bulb: First, calculate the energy consumption per lifetime. A 75 W bulb operating for its estimated lifetime (say, 1,200 hours) consumes:
- Energy = Power (kW) × Time (hours) = 0.075 kW × 1,200 hours = 90 kWh.
- Next, the electricity cost for the lifetime:
- Cost = 90 kWh × $0.10/kWh = $9.00.
- Adding the purchase price:
- Total lifetime cost = $1.00 + $9.00 = $10.00.
- Compact Fluorescent Bulb: Suppose the CFL lasts approximately 8,000 hours. Its energy consumption is:
- Power consumption = 13 W = 0.013 kW.
- Energy used over its lifetime:
- 0.013 kW × 8,000 hours = 104 kWh.
- Cost of electricity:
- 104 kWh × $0.10/kWh = $10.40.
- Adding the purchase price:
- Total lifetime cost = $7.00 + $10.40 = $17.40.
- Based on these typical values, the incandescent bulb has a lower total lifetime cost compared to the CFL over its estimated lifespan.
- Cost Analysis Over 7500 Hours
- Next, we compare costs for a 7,500-hour usage period, which corresponds to the lifespan of the CFL. For this period:
- Incandescent Bulb: Number of bulbs needed:
- Compact Fluorescent Bulb: Number of bulbs needed:
- Environmental Protection Agency (EPA). (2020). Climate Change & Energy. https://www.epa.gov/climate-change
- Energy Information Administration (EIA). (2022). U.S. Energy Facts. https://www.eia.gov/energyexplained/
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- U.S. Department of Energy. (2019). Choosing Energy-Efficient Light Bulbs. https://www.energy.gov/energysaver/design/lighting/energy-efficient-lighting
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7500 hours / 1,200 hours per bulb ≈ 6.25 bulbs, rounded up to 7 bulbs.
Total cost of bulbs:
7 × $1.00 = $7.00
Total energy consumption:
7 bulbs × 90 kWh (per bulb) = 630 kWh
Electricity cost:
630 kWh × $0.10 = $63.00
Total cost for incandescent bulbs over 7,500 hours:
$7.00 + $63.00 = $70.00
Since each CFL lasts approximately 8,000 hours, only one is necessary for 7,500 hours.
Energy consumption:
104 kWh (per bulb) for the full period, with electricity cost:
104 kWh × $0.10 = $10.40
Adding the purchase price:
$7.00 + $10.40 = $17.40
This analysis demonstrates that, over the same period, the CFL is significantly cheaper in total costs, mainly due to its longer lifespan and lower energy consumption per unit of light output.
Environmental Impact and Ecological Footprint
The ecological footprint of a light bulb extends beyond its cost to include the environmental consequences associated with electricity generation. In the United States, a substantial proportion of electricity is generated by fossil fuel power plants, predominantly coal and natural gas plants, which emit greenhouse gases and other pollutants.
Incandescent bulbs are energy-inefficient; they convert much of the electrical energy into heat rather than usable light. As a result, higher energy consumption translates into more fossil fuel burning, increasing atmospheric pollution and contributing to climate change. Correspondingly, their ecological footprint is larger, especially over their entire lifecycle.
On the other hand, compact fluorescent bulbs utilize energy more efficiently, producing more light per unit of energy consumed. Although CFLs contain small amounts of mercury, which requires careful disposal, their overall lower energy requirement reduces the demand on fossil fuel power plants, thus decreasing greenhouse gas emissions, air pollution, and resource depletion associated with electricity production.
Given that most U.S. electricity is produced from fossil fuels, switching to energy-efficient lighting like CFLs or LEDs markedly reduces ecological footprints. Hence, despite their potentially higher manufacturing impact due to rare materials, CFLs have a smaller overall ecological footprint over their lifespan because they lead to lower greenhouse gas emissions during use.
In conclusion, environmentally, compact fluorescent bulbs are the more sustainable choice compared to incandescent bulbs, primarily because they significantly reduce electricity consumption and associated atmospheric pollution, aligning with principles of sustainable energy use.
Summary
This analysis indicates that although incandescent bulbs may offer a lower initial purchase cost, their higher energy consumption and shorter lifespan lead to greater total costs and environmental harm over time. Compact fluorescent bulbs, while more expensive upfront, provide economic savings over their longer lifespan and contribute less to atmospheric pollution by reducing electricity demand from fossil fuel–burning plants. For individuals aiming to minimize both cost and ecological impact, energy-efficient lighting options like CFLs are advisable. Transitioning to improved lighting technologies, including LEDs, further enhances sustainability due to even greater energy efficiency and longer lifespans, representing a critical step towards reducing the ecological footprint of household lighting.