Switching a green traffic light from an incandescent bulb to an LED can result in significant energy and cost savings. Here’s a step-by-step breakdown of how to calculate the potential savings over the lifetime of the LED:
Assumptions for the Calculation:
Here are the assumed values for both the incandescent and LED green traffic lights:
Incandescent Bulb:
- Power Consumption: 135 watts (typical for green incandescent traffic lights).
- Lifespan: 8,000 hours.
- Cost per bulb: $5.
- Operating hours: 24 hours per day, 365 days per year (standard operation for traffic lights).
- Electricity rate: $0.12 per kilowatt-hour (kWh).
- Annual energy cost (incandescent): $141.91 (as calculated previously for similar bulbs).
- Maintenance cost per replacement: $55 (includes labor and cost of the bulb).
LED:
- Power Consumption: 15 watts (slightly higher than red or yellow LEDs because green LEDs typically require a bit more power).
- Lifespan: 50,000 hours.
- Cost of LED module: $100.
- Operating hours: 24 hours per day, 365 days per year.
- Electricity rate: $0.12 per kWh.
Step 1: Energy Consumption and Cost
Incandescent Bulb:
The annual energy consumption for a green incandescent bulb is:135 watts×24 hours/day×365 days/year=1,182,600 watt-hours/year=1,182.6 kWh/year135 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 1,182,600 \, \text{watt-hours/year} = 1,182.6 \, \text{kWh/year}135watts×24hours/day×365days/year=1,182,600watt-hours/year=1,182.6kWh/year
The annual energy cost for the incandescent bulb is:1,182.6 kWh/year×0.12 $/kWh=141.91 $ per year1,182.6 \, \text{kWh/year} \times 0.12 \, \text{\$/kWh} = 141.91 \, \text{\$ per year}1,182.6kWh/year×0.12$/kWh=141.91$ per year
LED Bulb:
The annual energy consumption for a green LED bulb is:15 watts×24 hours/day×365 days/year=131,400 watt-hours/year=131.4 kWh/year15 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 131,400 \, \text{watt-hours/year} = 131.4 \, \text{kWh/year}15watts×24hours/day×365days/year=131,400watt-hours/year=131.4kWh/year
The annual energy cost for the LED bulb is:131.4 kWh/year×0.12 $/kWh=15.77 $ per year131.4 \, \text{kWh/year} \times 0.12 \, \text{\$/kWh} = 15.77 \, \text{\$ per year}131.4kWh/year×0.12$/kWh=15.77$ per year
Step 2: Maintenance Costs
Incandescent Bulb:
- Incandescent bulbs last 8,000 hours, so they need to be replaced approximately every:
8,000 hours÷(24 hours/day)=333.3 days8,000 \, \text{hours} \div (24 \, \text{hours/day}) = 333.3 \, \text{days}8,000hours÷(24hours/day)=333.3days
- Over the 50,000-hour lifespan of an LED, the incandescent bulb will need to be replaced 6.25 times.
- The maintenance cost (including bulb and labor) per replacement is $55. Therefore, the total maintenance cost over the LED’s lifespan is:
6.25 replacements×55 $ per replacement=343.75 $ total maintenance cost6.25 \, \text{replacements} \times 55 \, \text{\$ per replacement} = 343.75 \, \text{\$ total maintenance cost}6.25replacements×55$ per replacement=343.75$ total maintenance cost
LED Bulb:
LEDs typically last 50,000 hours, meaning no replacements are required during this time. Therefore, the maintenance cost for the LED is $0.
Step 3: Total Lifetime Savings Over 50,000 Hours
Total Cost for Incandescent Bulb:
- Energy Cost (over 50,000 hours):
50,00024×365×141.91 $ per year=6.25 years×141.91 $ per year=886.94 $ total energy cost\frac{50,000}{24 \times 365} \times 141.91 \, \text{\$ per year} = 6.25 \, \text{years} \times 141.91 \, \text{\$ per year} = 886.94 \, \text{\$ total energy cost}24×36550,000×141.91$ per year=6.25years×141.91$ per year=886.94$ total energy cost
- Maintenance Cost: $343.75
- Total Cost for Incandescent Bulb:
886.94 $ (energy)+343.75 $ (maintenance)=1,230.69 $ total cost886.94 \, \text{\$ (energy)} + 343.75 \, \text{\$ (maintenance)} = 1,230.69 \, \text{\$ total cost}886.94$ (energy)+343.75$ (maintenance)=1,230.69$ total cost
Total Cost for LED:
- Energy Cost (over 50,000 hours):
50,00024×365×15.77 $ per year=6.25 years×15.77 $ per year=98.56 $ total energy cost\frac{50,000}{24 \times 365} \times 15.77 \, \text{\$ per year} = 6.25 \, \text{years} \times 15.77 \, \text{\$ per year} = 98.56 \, \text{\$ total energy cost}24×36550,000×15.77$ per year=6.25years×15.77$ per year=98.56$ total energy cost
- Maintenance Cost: $0
- Cost of LED Bulb: $100
- Total Cost for LED:
98.56 $ (energy)+100 $ (bulb)=198.56 $ total cost98.56 \, \text{\$ (energy)} + 100 \, \text{\$ (bulb)} = 198.56 \, \text{\$ total cost}98.56$ (energy)+100$ (bulb)=198.56$ total cost
Step 4: Total Savings Over the LED’s Lifetime
The savings from switching from an incandescent to an LED green traffic light over the LED’s 50,000-hour lifespan is:1,230.69 $ (incandescent total cost)−198.56 $ (LED total cost)=1,032.13 $ saved over the LED’s lifetime1,230.69 \, \text{\$ (incandescent total cost)} – 198.56 \, \text{\$ (LED total cost)} = 1,032.13 \, \text{\$ saved over the LED’s lifetime}1,230.69$ (incandescent total cost)−198.56$ (LED total cost)=1,032.13$ saved over the LED’s lifetime
Conclusion:
By switching from a green incandescent traffic light to a green LED, you can save approximately $1,032 over the lifetime of the LED (50,000 hours). These savings come from reduced energy consumption and significantly lower maintenance costs, making LED traffic lights a cost-effective and energy-efficient solution.
