Incandescent Exposure

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MAIN TOPIC OF VIDEO: Luminous efficacy

 Play Picture 2

DISCUSSION QUESTIONS:

Frame:

  1. What is the connection between light bulbs and climate change?
  2. How is light bulb efficiency measured?
  3. What type of lighting is most commonly used in homes?

Focus:

  1. When the lady says that incandescent light bulbs are very inefficient because they give off more heat than light, what does she mean?
  2. What are the three light bulbs being compared in the video?

Lightbulbs

3.  The characters in the video were arguing about the cost of the bulbs compared to how long they would last. What makes the new light bulbs the better choice?

Follow-up:

  1. What kind of light bulbs do you currently use at home? What could you do to help your energy use be more efficient?
  2. A 60-watt incandescent light bulb produces 800 lumens. The equivalent in CFLs only uses 13 watts. Calculate each bulb’s efficiency in lumens per watt.
  3. According to the “Home Lighting” document published by San Diego Gas & Electric, how do the bulbs from the previous question compared in terms of lifespan and annual energy cost? See: Home Lighting 

Is the lady correct in saying that energy-efficient bulbs last much longer and cost much less to provide the same amount of lighting?

 

ANSWERS TO DISCUSSION QUESTIONS

Frame:

1. What is the connection between light bulbs and climate change?

  • Light bulbs use electricity, and most electricity is still created using fossil fuels. When we burn fossil fuels, carbon dioxide (the #1 contributor to global greenhouse gas emissions) is released.

2. How is light bulb efficiency measured?

  • Light bulb efficiency is measured in lumens per watt. Lumens are the amount of light produced by a bulb. Wattage is the amount of electricity needed to light the bulb. Divide the light bulb’s lumen output by the number of watts the bulb needs in order to get lumens per watt (LPW).

3. What type of lighting is most commonly used in homes?

  • Incandescent lighting is the most commonly used light source in homes (due to low cost). However, in recent years, CFLs (compact fluorescent lamp) have become very popular because they are much more efficient than incandescent light bulbs and still have a relatively low-cost.

Focus:

1. When the lady says that incandescent light bulbs are very inefficient because they give off more heat than light, what does she mean?

  • Incandescent bulbs convert less than 5% of the energy they use into visible light (with the remaining energy being converted into heat. When over 95% of the energy used is emitted as heat, the light bulb is extremely inefficient with regards to its intended purpose. Can you imagine the amount of heat it emits to light up a room and then having to turn on air conditioning just to offset that heat?

2. What are the three light bulbs being compared in the video?

Lightbulbs

  • From left to right: CFL (compact fluorescent lamp), incandescent, LED (light-emitting diode).

3. The characters in the video were arguing about the cost of the bulbs compared to how long they would last. What makes the new light bulbs the better choice?

  • Even though the new light bulbs like CFLs and LEDs cost more than incandescent light bulbs, they are more energy-efficient and also last much longer. In the long run, they cost much less to provide the same amount of lighting.

Follow-up:

1. What kind of light bulbs do you currently use at home? What could you do to help your energy use be more efficient?

  • Answers may vary for the first question. Energy use can become more efficient by replacing all incandescent light bulbs with CFLs (or even better — LEDs).

2. A 60-watt incandescent light bulb produces 800 lumens. The equivalent in CFLs only uses 13 watts. Calculate each bulb’s efficiency in lumens per watt. Which one is more efficient?

Incandescent light bulb: 800 lumens divided by 60 watts = 13.3 lumens per watt

CFL: 800 lumens divided by 13 watts = 61.5 lumens per watt

Since 61.5 LPW > 13.3 LPW, CFLs are much more efficient!

However, LEDs are even more efficient — examine this chart to see how LED lighting trumps the other two!

        https://www.designrecycleinc.com/led%20comp%20chart.html

3. According to the “Home Lighting” document published by San Diego Gas & Electric, how do the bulbs from the previous question compared in terms of lifespan and annual energy cost?

See: Home Lighting

Is the lady correct in saying that energy-efficient bulbs last much longer and cost much less to provide the same amount of lighting?

  • The incandescent light bulb will last 750 hours, and cost $6.57 over the course of the year. The CFL will last 8,000 hours and cost $1.42 over the course of the year. Yes, the lady is correct in saying that energy-efficient bulbs last much longer and cost much less to provide the same amount of lighting.

 

ADDITIONAL TOPICS AND LEARNING EXPERIENCES

1. At the end of the video, the man asked the lady if she wanted to buy some coal. What’s the connection between coal and light bulbs?

  • As discussed earlier in Frame Question #1, most electricity is still produced by burning fossil fuels. Coal, one type of fossil fuel, supplies about 39% of electricity generated in the United States.

IE-graph2. Using energy-efficient light bulbs certainly help to reduce the amount of energy used overall. But most electricity is still created using fossil fuels, a huge contributor to atmospheric warming. Are there cleaner alternatives to electricity production other than using fossil fuels?

  • Yes. Nuclear power currently supplies about 19% of electricity generation, and renewable resources supply about 13%. According to the U.S. Energy Information Administration, we’re not using more renewable energy because it’s more expensive to produce and unreliable as a source. Although the use of renewable energy is expected to grow over the next 30 years, we will most likely still rely on non-renewable sources to meet most of our energy needs. See: Renewable home 

 

ADDITIONAL NOTES AND RESOURCES

  • Use this Lighting Calculator for a lesson on calculating kilowatt-hours (kWh) and how much money could be saved/how much CO2 avoided.

https://www.mge.com/saving-energy/home/lighting/

https://www.mge.com/saving-energy/home/lighting/light-show-no-search.htm

  • Energy Star’s Interactive Guide to Choosing Lights – Click here
  • CFL lights are a great because they save energy, but they contain mercury and could be harmful if they break. For more information of the precautions to take when using them at home see:

1. Energy Star’s Frequently Asked Questions sheet PDF

2. Environmental Protection Agency’s (EPA’s) website – Click here

  • The Energy Information Administration’s website for kids provides information for students to explore energy topics on their own as well as lesson plans for teachers:

https://www.eia.gov/kids/

  •  Short activity involving math exercises used to calculate the Energy, in kWh, the CO2 emissions (in lbs of CO2), the cost for the bulb, and energy for two types of bulbs is provided  PDF

 

Credit: This teacher resource has been adapted from content originally developed by Hannah Sun.

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