Lesson 7
Overhead 1 of 5
Diagram of an Incandescent Light Bulb
From http://home.howstuffworks.com/light-bulb1.htm
Lesson 7
Overhead 2 of 5
http://hackadaycom.files.wordpress.com/2013/10/led-low1.jpg
Lesson 7
Overhead 3 of 5
http://hackadaycom.files.wordpress.com/2013/10/led-low1.jpg
Lesson 7
Handout
In the 20th century, energy was cheap. So, light
bulbs were not very efficient. They weren’t much
different from the bulb Thomas Edison developed
in the 19th century. Edison’s 1879 bulb, the
incandescent, wasted 90% of its energy as heat.
Only 1/10th of the electricity was turned into light!
Now, we need bulbs that are much more
efficient. Some excellent types are available; two
are the CFL and the LED (light emitting diode).
The CFL, or Compact Fluorescent Lamp uses
approx. 75% less energy than the incandescent, but
gives the same number of lumens. A lumen is a
measure of light. To give 950 lumens of light, the
incandescent consumes 70 watts of power. The
CFL? Only 15 watts. Also, where the incandescent
burns for 1000 hours, the CFL lasts 10,000 hours.
One CFL disadvantage; it has mercury in it, so care
must be taken in using and recycling.
Then, along came the LED.
Actually, LEDs have been around since the
1950s, when scientists working on radios, TVs and
computers noticed certain semi-conductors glowed
when a small current was applied. LEDs are so
efficient, they give 940 lumens using only 10 watts
of power. LED stands for Light Emitting Diode. A
diode is an electronic component that allows
current to flow through it, but only in one
direction.
The diode itself is very small, so 9 or 10 are put
into a glass bulb similar in size to the incandescent
bulb. Also inside are very precise computer parts
and power converters. The LED household bulb is
quite complicated, but rugged. Some LEDs give
light for up to 45,000 hours.
CFL (compact fluorescent)
Bulb Life = 10,000 hours
Cost per Bulb = $3.50
Power Consumption = 15 watts
LED (light emitting diode)
Bulb Life = 30,000 hours
Cost per Bulb = $10.50
Power Consumption = 10 watts
How much CO2 is produced by a coal fired plant,
when it lights our bulbs?
On the back of this sheet, we’re lighting bulbs for
30,000 hours, so 30,000 hrs X .015 kW X 1.3 lb CO2
per kWh = 585 pounds of CO2.
How much CO2 is produced by a coal fired power
plant, when it lights our bulb? Well, 30,000 hours X
.01 kW X 1.3 lb CO2 per kWh = 390 pounds of CO2.
Sources: http://ledbulbreview.wordpress.com/
http://www.energystar.gov/certified-products/detail/508/partners
Lesson 7
Handout
Name ___________________________________________
How much can you save using more efficient bulbs?
The graphic on the previous page shows two bulbs that produce approximately the same amount of light.
You may use bulbs like them in your home. One bulb is a CFL (compact fluorescent lamp). The other is a LED
(light emitting diode). Which is the better bargain? Let’s do the math and compare the two bulbs, using the
residential cost of electric energy at $0.11/kWhr.
1. Determine how many bulbs you will need to produce 30,000 hours of light by dividing 30,000 by the
number of hours each bulb produces light.
2. Multiply the number of bulbs you will need by the cost of each bulb to determine the cost of bulbs to
produce 30,000 hours of light.
3. Multiply the wattage of the bulbs by 30,000 hours to determine the watt-hours (Wh). Then divide by
1000 to determine the number of kilowatt-hours (kWh).
4. Multiply the number of kilowatt-hours by the cost per kilowatt-hour to determine the cost of
electricity to produce 30,000 hours of light.
Lesson 7
Handout
ANSWER SHEET
Name ___________________________________________
How much can you save using more efficient bulbs?
The graphic on the previous page shows two bulbs that produce approximately the same amount of light.
You may use bulbs like them in your home. One bulb is a CFL (compact fluorescent lamp). The other is a LED
(light emitting diode). Which is the better bargain? Let’s do the math and compare the two bulbs, using the
residential cost of electric energy at $0.11/kWhr.
5. Determine how many bulbs you will need to produce 30,000 hours of light by dividing 30,000 by the
number of hours each bulb produces light.
6. Multiply the number of bulbs you will need by the cost of each bulb to determine the cost of bulbs to
produce 30,000 hours of light.
7. Multiply the wattage of the bulbs by 30,000 hours to determine the watt-hours (Wh). Then divide by
1000 to determine the number of kilowatt-hours (kWh).
8. Multiply the number of kilowatt-hours by the cost per kilowatt-hour to determine the cost of
electricity to produce 30,000 hours of light.
$10.50
$49.50
$60.00
$10.50
$33.00
$43.50
$60.00
$43.50
$16.50
Lesson 7
Overhead 4 of 5
Making a Homemade Flashlight:
What’s Needed for a Successful Closed Circuit?
1. Electrical source: battery
2. A pathway for the electricity: aluminum foil and wires in the light bulb
3. A load (something for the electricity to power): light bulb
Lesson 7
Overhead 5 of 5
Handout
“Making A Flashlight”
Name: ______________________________
Will the bulb light? Below each picture, make your prediction by writing either “On” or “Off.”
List the numbers of the pictures above that show a closed circuit _______________________________