Switching out a red traffic light from an incandescent bulb to an LED can result in significant savings due to the reduced energy consumption and longer lifespan of LEDs. Let’s break down the calculation of potential savings over the lifetime of the LED, taking into account energy usage, maintenance costs, and bulb longevity.
Assumptions for Calculation:
To make the calculation, we need to assume certain values for both the incandescent bulb and the LED:
Incandescent Bulb:
- Power Consumption: 135 watts (standard for a red incandescent traffic light).
- Lifespan: 8,000 hours (incandescent traffic lights last longer than household bulbs due to specialized designs).
- Cost per bulb: $5 (approximate cost of an incandescent traffic light bulb).
- Operating Hours: 24 hours a day, 365 days a year (common for traffic lights).
- Electricity Rate: $0.12 per kilowatt-hour (kWh) (this rate can vary depending on location).
LED:
- Power Consumption: 10 watts (standard for a red LED traffic light).
- Lifespan: 50,000 hours (average lifespan of a traffic light LED).
- Cost per bulb: $100 (initial cost of an LED traffic light module, including driver).
- Operating Hours: 24 hours a day, 365 days a year.
- Electricity Rate: $0.12 per kWh.
1. Energy Consumption and Cost of Incandescent Bulb:
Annual Energy Use:
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
Annual Energy Cost:
1,182.6 kWh/year×0.12 $/kWh=141.91 $/year1,182.6 \, \text{kWh/year} \times 0.12 \, \text{\$/kWh} = 141.91 \, \text{\$/year}1,182.6kWh/year×0.12$/kWh=141.91$/year
2. Energy Consumption and Cost of LED:
Annual Energy Use:
10 watts×24 hours/day×365 days/year=87,600 watt-hours/year=87.6 kWh/year10 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 87,600 \, \text{watt-hours/year} = 87.6 \, \text{kWh/year}10watts×24hours/day×365days/year=87,600watt-hours/year=87.6kWh/year
Annual Energy Cost:
87.6 kWh/year×0.12 $/kWh=10.51 $/year87.6 \, \text{kWh/year} \times 0.12 \, \text{\$/kWh} = 10.51 \, \text{\$/year}87.6kWh/year×0.12$/kWh=10.51$/year
3. Maintenance Costs:
Incandescent Bulb Replacement Frequency:
- Incandescent bulbs last 8,000 hours, so with 24-hour operation, they need to be replaced 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
- This means you would need to replace the incandescent bulb approximately 6.25 times over 50,000 hours (the lifespan of one LED).
Maintenance Costs for Incandescent Bulbs:
- Cost per replacement: $5 for the bulb, plus an estimated $50 for labor per replacement (this varies but is a good average for the cost of sending a crew to replace the light).
- Over the lifespan of the LED (50,000 hours), you would need to replace the incandescent bulb 6.25 times:
6.25 replacements×(5 $ per bulb+50 $ labor)=343.75 $ total maintenance cost for incandescent bulbs6.25 \, \text{replacements} \times (5 \, \text{\$ per bulb} + 50 \, \text{\$ labor}) = 343.75 \, \text{\$ total maintenance cost for incandescent bulbs}6.25replacements×(5$ per bulb+50$ labor)=343.75$ total maintenance cost for incandescent bulbs
LED Maintenance Costs:
- LEDs last 50,000 hours, so during this period, the LED bulb does not need to be replaced. Therefore, the maintenance cost over the same period is $0.
4. Total Savings Over LED Lifespan (50,000 hours):
Total Cost for Incandescent Bulb (50,000 hours):
- Energy Cost (over 50,000 hours):
50,00024×365×141.91 $/year≈6.25 years×141.91 $/year=886.94 $ for energy\frac{50,000}{24 \times 365} \times 141.91 \, \text{\$/year} \approx 6.25 \, \text{years} \times 141.91 \, \text{\$/year} = 886.94 \, \text{\$ for energy}24×36550,000×141.91$/year≈6.25years×141.91$/year=886.94$ for energy
- 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 (50,000 hours):
- Energy Cost (over 50,000 hours):
50,00024×365×10.51 $/year=6.25 years×10.51 $/year=65.69 $ for energy\frac{50,000}{24 \times 365} \times 10.51 \, \text{\$/year} = 6.25 \, \text{years} \times 10.51 \, \text{\$/year} = 65.69 \, \text{\$ for energy}24×36550,000×10.51$/year=6.25years×10.51$/year=65.69$ for energy
- Maintenance Cost: $0
- Cost of LED Bulb: $100
- Total Cost for LED:
65.69 $ (energy)+100 $ (bulb)=165.69 $ total cost65.69 \, \text{\$ (energy)} + 100 \, \text{\$ (bulb)} = 165.69 \, \text{\$ total cost}65.69$ (energy)+100$ (bulb)=165.69$ total cost
5. Total Savings Over LED Lifespan:
1,230.69 $ (incandescent cost)−165.69 $ (LED cost)=1,065 $ saved over the LED’s lifetime1,230.69 \, \text{\$ (incandescent cost)} – 165.69 \, \text{\$ (LED cost)} = 1,065 \, \text{\$ saved over the LED’s lifetime}1,230.69$ (incandescent cost)−165.69$ (LED cost)=1,065$ saved over the LED’s lifetime
Conclusion:
By switching from a 135-watt incandescent red traffic light to a 10-watt LED over the lifespan of the LED (50,000 hours), you could save approximately $1,065 per traffic light in energy and maintenance costs. These savings multiply significantly when scaled across an entire city or large municipality where hundreds or thousands of traffic lights are in operation.