To calculate how much pollution (specifically carbon dioxide, or CO₂ emissions) is prevented by switching an average intersection from incandescent bulbs to LEDs, we will use the following factors:
- Number of lights at an average intersection:
- Typically, there are 3 lights per traffic signal (red, yellow, and green).
- At a 4-way intersection, there are usually 4 signal heads (one for each direction).
- This results in a total of 12 lights per intersection.
- Power consumption of incandescent vs. LED traffic lights:
- Incandescent bulbs: Use 135 watts per bulb for red, yellow, and green lights.
- LED bulbs: Use 10 watts (red and yellow) and 15 watts (green).
- Operating time: Traffic lights generally operate 24 hours per day, 365 days per year.
- CO₂ emissions per kilowatt-hour (kWh): The average emissions are approximately 0.42 kilograms of CO₂ per kWh (or 0.92 pounds per kWh), based on U.S. EPA data.
Step 1: Calculate Energy Use for Incandescent Traffic Lights
Energy consumption per incandescent light (annual):
135 watts×24 hours/day×365 days/year=1,182.6 kWh/year per light135 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 1,182.6 \, \text{kWh/year per light}135watts×24hours/day×365days/year=1,182.6kWh/year per light
Since there are 12 incandescent lights at an intersection:1,182.6 kWh/year×12 lights=14,191.2 kWh/year for the entire intersection1,182.6 \, \text{kWh/year} \times 12 \, \text{lights} = 14,191.2 \, \text{kWh/year for the entire intersection}1,182.6kWh/year×12lights=14,191.2kWh/year for the entire intersection
Step 2: Calculate Energy Use for LED Traffic Lights
LED power consumption:
- Red and yellow LEDs use 10 watts.
- Green LEDs use 15 watts.
Energy consumption per LED light (annual):
For red and yellow LEDs:10 watts×24 hours/day×365 days/year=87.6 kWh/year per light10 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 87.6 \, \text{kWh/year per light}10watts×24hours/day×365days/year=87.6kWh/year per light
For green LEDs:15 watts×24 hours/day×365 days/year=131.4 kWh/year per light15 \, \text{watts} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 131.4 \, \text{kWh/year per light}15watts×24hours/day×365days/year=131.4kWh/year per light
With 4 red, 4 yellow, and 4 green lights at an intersection:(87.6 kWh/year×8 red and yellow lights)+(131.4 kWh/year×4 green lights)=1,372.8 kWh/year (red and yellow)+525.6 kWh/year (green)=1,898.4 kWh/year for the entire intersection(87.6 \, \text{kWh/year} \times 8 \, \text{red and yellow lights}) + (131.4 \, \text{kWh/year} \times 4 \, \text{green lights}) = 1,372.8 \, \text{kWh/year (red and yellow)} + 525.6 \, \text{kWh/year (green)} = 1,898.4 \, \text{kWh/year for the entire intersection}(87.6kWh/year×8red and yellow lights)+(131.4kWh/year×4green lights)=1,372.8kWh/year (red and yellow)+525.6kWh/year (green)=1,898.4kWh/year for the entire intersection
Step 3: Energy Savings from Switching to LEDs
The total energy saved by switching to LEDs is:14,191.2 kWh/year (incandescent)−1,898.4 kWh/year (LED)=12,292.8 kWh/year saved14,191.2 \, \text{kWh/year (incandescent)} – 1,898.4 \, \text{kWh/year (LED)} = 12,292.8 \, \text{kWh/year saved}14,191.2kWh/year (incandescent)−1,898.4kWh/year (LED)=12,292.8kWh/year saved
Step 4: Calculate CO₂ Emissions Prevented
Using the CO₂ emissions factor of 0.42 kg of CO₂ per kWh, the amount of CO₂ emissions prevented is:12,292.8 kWh/year×0.42 kg CO₂/kWh=5,162.98 kg CO₂/year (or 5.16 metric tons per year)12,292.8 \, \text{kWh/year} \times 0.42 \, \text{kg CO₂/kWh} = 5,162.98 \, \text{kg CO₂/year} \, \text{(or 5.16 metric tons per year)}12,292.8kWh/year×0.42kg CO₂/kWh=5,162.98kg CO₂/year(or 5.16 metric tons per year)
Step 5: CO₂ Emissions Prevented Over the LED’s Lifetime
The average LED traffic light has a lifespan of 50,000 hours, which equals about 5.7 years of continuous operation.
Thus, the total amount of CO₂ emissions prevented over the LED’s lifespan is:5,162.98 kg/year×5.7 years=29,429 kg of CO₂ prevented over the LED’s lifetime (or 29.43 metric tons)5,162.98 \, \text{kg/year} \times 5.7 \, \text{years} = 29,429 \, \text{kg of CO₂ prevented over the LED’s lifetime} \, \text{(or 29.43 metric tons)}5,162.98kg/year×5.7years=29,429kg of CO₂ prevented over the LED’s lifetime(or 29.43 metric tons)
Conclusion:
By switching an average 4-way intersection from incandescent traffic lights to LEDs, you can prevent approximately 5.16 metric tons of CO₂ emissions per year. Over the 5.7-year lifespan of the LEDs, the total reduction in emissions would be around 29.43 metric tons of CO₂. This substantial reduction in emissions highlights the environmental benefits of transitioning to energy-efficient LED traffic lights.
