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Sustainability Lesson Clearinghouse

Calculating the Life-Time Cost of Light Bulbs

Lesson Description:
In this activity, your students will address two common misconceptions.

The first is that the purchase price of an item reflects its real cost. In reality, people must also consider the ongoing operating costs of an item over its lifetime. these costs include maintenance, fuel, service fees, financing charges, and repair/replacement. Lifetime costing can show that an item that appears to be cheap or even free up-front can be much more expensive in the long run. Cellular telephones represent a familiar example of this concept: companies give them away and recoup their investment by selling the service. in this activity, your students will see that while common incandescent light bulbs cost very little to buy, their lifetime operating costs make them costly in the long run.
The second misconception is that “watts” are a measure of light output (after all, a 100-watt bulb is brighter than a 60-watt, isn’t it?). Actually, watts are a measure of electrical consumption while “lumens” are a measure of light. A nice way to frame the question is this: “when you flip the light switch, is your goal to buy electricity or to buy light?” if your concern is buying electricity, buy according to the wattage; if your goal is buying light, shop for the most lumens that require the least wattage. This activity compares the real cost of two different kinds of light bulbs, both of which deliver the same amount of light (number of lumens): a common incandescent bulb and a high-efficiency compact fluorescent bulb.

Lesson Type:

Sustainability Topic:

Time Needed:
80 minutes

Standards Addressed:
By doing this activity students will:

Understand that energy can be transformed from one form to another.
Electrical energy can be transformed into heat and light.
Different types of lighting devices use different means to transform electrical energy into light.
Light bulbs that produce heat as well as light are inefficient and waste energy on unwanted outcomes.
The true cost of an appliance (even as simple as a light bulb) must take into account its lifetime operating cost, including energy consumption and replacement costs.

Materials Needed: