Welcome to Lesson 8!
In 2020, 81 billion kWh of electricity was used for lighting homes in the US. Commercial buildings added 208 billion kWh and industrial facilities added another 53 billion kWh. This means in the US, we spend literally billions of dollars to light our environment. Additionally, this means tons of additional carbon emissions, into the atmosphere.
The good news? Lighting is one of the easiest places to save energy.
- Switching just five frequently used bulbs to LED can save ~$75/year and prevent ~1,000 lbs of CO₂ emissions.
- Upgrading lighting in a school, office, or community building can cut energy costs by 50% or more.
The Lighting Revolution: Then → Now
| Era | Dominant Technology | Typical Efficacy |
|---|---|---|
| ~2000 | Incandescent bulbs | 10–17 lumens/watt |
| ~2010 | Compact Fluorescent (CFL) | 50–70 lumens/watt |
| Today | LED (Light-Emitting Diode) | 80–150+ lumens/watt |
Twenty years ago, nearly every home used incandescent bulbs. Today, LEDs dominate the market because they:
- Use up to 90% less energy than incandescents
- Last 15–25+ years (vs. 1–2 years for incandescents)
- Contain no mercury (unlike CFLs)
- Offer instant-on, dimmable, high-quality light in warm or cool tones
In this lesson, we'll explore how each technology works—and why LEDs represent the most efficient way to generate visible light today.
Key Concepts We'll Cover
Light Measurement Basics
- Lumens = total visible light output (brightness)
- Watts = energy consumed (not brightness!)
- Foot-candles = light received on a surface (lumens per square foot)
- CRI (Color Rendering Index) = how true colors appear under a lamp (0–100 scale)
Life-Cycle Cost Analysis
We'll practice the most important calculation in this lesson: comparing the total cost of ownership for different lamps. This includes:
- Purchase price × number of replacements needed
- Energy costs over the lamp's lifetime
- Maintenance and disposal considerations
Remember: The cheapest bulb upfront isn't always the cheapest over time.
Smart Lighting Strategies
- Matching light levels to tasks (reading vs. hallway vs. accent lighting)
- Using controls (timers, motion sensors, dimmers, photocells) to eliminate waste
- Retrofitting existing fixtures for better efficiency
Lighting
These are some statistics on lighting in the US. The latest report from the Office of Energy Efficiency and Renewable Energy was put out in April 2024, but it refers to a study from 2020.
- Lighting accounts for 4% of all electricity consumed in the United States. This has been steadily decreasing as more energy-efficient lighting options have come on the market in
- An average household dedicates 6% percent of its energy budget to lighting. Commercial establishments consume about 17% percent of their total energy just for lighting.
- Technologies developed during the past 25 years, specifically LED lightings, have helped cut lighting costs 30 to 75 percent while enhancing lighting quality and reducing environmental impacts.
Lesson 8 Objectives
Upon completing this lesson, students will be able to:
- Explain how different lamp types (incandescent, halogen, fluorescent, HID, LED) produce light
- Compare lighting efficiency using lumens, watts, and lumens per watt
- Identify lighting controls that reduce waste without sacrificing comfort
- Perform a life-cycle cost analysis to compare total ownership costs
Questions?
If you have any questions, please post them to the General Course Questions forum located in the Discussions tab in Canvas. While you are visiting the discussion board, feel free to post your own responses to questions posted by others - this way, you might help a classmate!