An energy-efficient lightbulb, taking in 26.0 W of power, can produce the same l

Question

An energy-efficient lightbulb, taking in 26.0 W of power, can produce the same level of brightness as a conventional lightbulb operating at power 100 W. The lifetime of the energy-efficient bulb is 10 000 h and its purchase price is $4.40, whereas the conventional bulb has lifetime 750 h and costs $0.44 per bulb. Determine the total savings obtained by using one energy-efficient bulb over its lifetime as opposed to using conventional bulbs over the same time period. Assume an energy cost of $0.20 per kilowatt- hour. $

Explanation / Answer

To determine the energy cost, multiply the number of kilowatts times the number of hours, and then multiply by $0.2.

For the energy-efficient bulb, cost = 0.026. * 10,000 * 0.2 = $52
Total cost = 52 + 4.40 = $56.40

Let’s use the same method to determine the energy cost of the conventional bulb for 750 hours.

Cost = 0.1 * 750 * 0.2 = $15

To determine the number of conventional bulbs that will last the same time as the high-efficiency bulb, divide the life times of the two bulbs.

Number = 10,000 ÷ 750 = 13 bulbs
For the conventional bulb, cost = 13 * 15 = $200
Cost of 13 bulbs = 13 * 0.44 = $5.86
Total cost = 200 + 5.86 = $205.86

Savings = $205.86 – $56.40 = $149.46
.

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