Review and Extra Resources

EGEE 102 Lesson 6 Review

For task lighting a specific task, specific task meaning either reading or writing or cooking or repairing something, that requires generally about 40 to 50 foot candles. Sometimes, if you're working on small objects, you may need even a little more light. Accent lighting is the lighting that is used to highlight certain things at home, for example, a painting or a statue or something you want to highlight.

And you should be able to design lighting for certain areas. That's something that you may want to look at. Let's say you're designing for a general purpose hallway. You have 10 square feet, and each square foot requires about 10 lumens, which means 100 square feet requires 1,000 lumens. So you should be able to figure that out.

Color rendering index - different lighting produces different abilities to look at true colors. And you need to know the color rendering index. It is measured on a scale from zero to 100, and 100 being perfect colors or absolutely no color shift. And that is generally possible in natural light.

And when you have a room, how many lamps are required? That depends on how many lumens. You need total area and lumens, and each bulb gives out a certain number of lumens, and how many bulbs you require is based on that.

For example, if you have a room of 100 square feet, you need, let's say, 20 foot candles, which means 20 lumens per square foot. So every square foot requires 20 lumens. So in this case, 20 times 100 would be 2,000 lumens needed for that room.

And let's say if a 60-watt bulb gives you 1,000 lumens, you need two of these bulbs to get that 2,000 lumens. Of course, there are other factors like reflections off the walls and also the light fixture efficiency and so on and so forth. So you need to know the factors that affect, particularly the number of lamps required.

Types of lighting - you need to know the differences between incandescence, fluorescence, and high-intensity discharge lamps - how you produce the light, the process, and the hardware that is involved. And you should be able to perform life-cycle analysis. In other words, if you have two different types of light, for example an incandescent light and a CFL bulb - you are able to perform a life-cycle analysis using these two bulbs.

Life cycle analysis is cost to own and operate for the entire lifetime of the bulb. And remember, you have to compare for the same life period. These are not different lifetimes. If one bulb lasts 1,000 hours, and the other one last 8,000 hours, you have to use eight of these 1,000-hour bulbs to compare, actually. And cost to own, cost to supply the energy, energy cost, and maintenance costs together will be the lifetime cost.

Test Yourself

The questions below are your chance to test and practice your understanding of the content covered in this lesson. In other words, you should be able to answer the following questions if you know the material that was just covered! If you have problems with any of the items, feel free to post your question on the unit message board so your classmates, and/or your instructor, can help you out!

1. How is light measured?
2. What factors determine the amount of light that is needed in a room?
3. What are the three main methods of producing light?
4. Explain the difference between incandescence, fluorescence, and high intensity discharge.
5. What are the common ways in which we can improve energy efficiency?
6. A 60-watt light bulb produces 3 watts of radiant energy and 57 watts of heat energy. What is its efficiency?
7. A 100-watt light bulb is left on all day (24 hours). How much did it cost to operate the light bulb if electricity costs 5 cents per kWh?
8. A 100 watt incandescent light bulb is operated for 12 hours, and a 15 watt fluorescent light bulb is operated for the same period of time. At 10 cents per kWh, what are the cost savings of the fluorescent bulb?
9. Jackie Smith, who is very conscious about the environment, would like to know how much energy she can save by switching to fluorescent bulbs. Estimate the total energy savings for Jackie, who uses a light bulb fixture, by comparing the total costs to own and operate a 23-Watt CFL bulb instead of the 100 Watt incandescent bulb that she has been using. The expected life of incandescent and CFL bulbs is 1000 h and, 8000 hours. The purchase price of an incandescent bulb is \$0.50 and the CFL is \$7.50. If Jackie Smith replaces 24 bulbs at home with CFLs, what would her savings be if the electricity cost is \$0.085 per kWh?

Extra Resources

For more information on topics discussed in Lesson 6, see these selected references:

1. Energy.gov Office of Energy Efficiency and Renewable Energy [1]
2. GE Consumer Lighting [2]
3. Don Klipstein's Lighting [3]
4. Energy.gov Building Technologies Office [4]