Lighting Efficiency

Lighting Efficiency Problem Suppose that 25 incandescent light bulbs rated at 100 Watt are replaced by 25 fluorescent lamps rated at 20 Watts. The lifetime of the fluorescent bulbs is 10,000 hours of operation.

1. How much energy (in kWh) is consumed by the 25 incandescent 100 Watt bulbs during 10,000 hours of operation (their lifetime)? Energy Consumed = = 25 bulbs 100 W/bulb 10,000 h = 25,000,000 Wh = 25,000 kWh

2. How much energy (in kWh) is consumed by the 25 fluorescent 20 Watt bulbs during 10,000 hours of operation (their lifetime)? Energy consumed = = 25 bulbs 20 W/bulb 10,000 h = 5,000,000 Wh = 5,000 kWh

3. How much energy is saved by replacing the 25 incandescent bulbs by 25 fluorescent bulbs? Energy Saved = = 25,000 kWh – 5,000 kWh = 20,000 kWh

4. How much money is saved, assuming that the cost of electricity equals $0.10/kWh? Money Saved = = 20,000 kWh $0.10/kWh = $2,000

5. What is the payback period assuming the fluorescent bulbs cost $8 each? Cost = $8/bulb 25 bulbs = $200 Savings= $2,000 / 10,000 h of use Payback = Cost / Savings = ,000 h of use = 1,000 h of use