Incandescent  and  Fluorescent
Question: How are incandescent and fluorescent lights related?

Study Focus: This lesson will introduce students to the Watt-Rate meter by analyzing the differences between light produced from incandescent bulbs and fluorescent bulbs
Skills: Computing, Graphing, Analyzing
Objectives: After completing the activity, students will be able to:
Observe, record, and interpret data.
Use charts, tables, and graphs.
Identify how energy is measured, and read a Watt-rate meter.
Communicate ways that changes in behaviors can affect energy consumption.

OR Science Standards

Benchmark 3
The Dynamic Earth
Forming the Question

The Dynamic Earth
Forming the Question

Watt-Rate meter

Light sources

Foot Candle/Lux Meter

Discuss the differences between the two types of lighting. These web sites will give you a good idea of the science behind these technologies.

Incandescent lights

Fluorescent lights

1. There are two sets of bulb supplied in the kit you received from the EWEB team Start your study with incandescent bulb strips (100 watts).

Caution: The incandescent bulbs will get very hot. Handle with care and use safety glasses.

Have students record the kWh used in 5 minutes by the bulbs. Here’s a good chance to practice the meter reading skills learned in the previous lesson.

Replace the incandescent bulb strips with fluorescent bulb strips (230 watts) and again record the kWh used in 5 minutes.

Here are some important questions students might ask relevant to these readings?

Why do we use these bulbs?
Is the energy used the only factor that is important?
What measurements need to be added to our discussion to help determine which type of bulb fits our needs best for --- Variable lighting!!! Cool lights!!! Continuous lighting!!! Cheap lighting!!! Bulb life!!!
How do we measure light output? What is the unit of measure?

2. You have been supplied with a Foot Candle/Lux Meter and thermometers. Help students devise experiments to measure delivered light and heat produced by the two light sources. Put some emphasis on real life situations such as proper light for reading or for close project work. Recommended light levels can be found on the web!
Recommended light levels can be found on the web!

Some calculations you might want to challenge you student with:

The following information was taken from the labels on the packages of bulbs you have been supplied.

Incandescent lights

GE Soft white 100, 2x Life (Advertised to last 2x regular bulbs)
Cost: per bulb $.486
Life expectancy 1,500 hours
Watts 100
Lumens 1,530

Fluorescent lights

N:vision soft white, Energy Star
Cost: per bulb $1.661
Life expectancy 10,000 hours (at 3 hours per day)
Watts 23
Lumens 1,600

Save up to $308 per bulb at $0.10 per kWh


1. How much more electricity does the 100 watt bulb require than the 23 watt bulb (from information on the purchase package)?
100 watts – 23 watts = 67 watts
100 watts / 23 watts = 4.35 times as much electricity used.

2. With ten 100 watt bulbs attached to the Watt-Rate meter I recorded 26 seconds for the flat disk to rotate once. With 10 fluorescent bulbs it took the plate 101 seconds for one rotation.

How do these experimental numbers compare to the numbers calculated from the information supplied when buying the bulbs?

1.41 seconds / 26 seconds = 3.88 times as long for one rotation.
Why is the experimental number different from the number derived from information supplied on the purchase package?

3. What is the price comparison between the two types of bulbs?

$.486 per bulb / 1500 hours = $.00032 per bulb / hour

$1.66 per bulb / 10000 hours = $.00016 per bulb / hour