# how much energy & money do new light bulbs save?

Last updated: July 27, 2020

Math Skill: Multiplication

Science Subject: Our Energy Resources

Environmental Area: Energy

Purpose: Understand how much electricity and money wecan save by changing light bulbs to energy saving ones and develop awareness of energy conservation

### BACKGROUND FOR THE TEACHER

Replacing light bulbs from incandescent light bulbs to compact fluorescent bulbs or LED lamps is one of the easiest ways to reduce electricity use. Compact fluorescent light bulbs and LED lamps can convert electrical energy into useful light much more efficiently than incandescent bulbs and have several times the luminous efficacy of an incandescent bulb with comparable light output.

A typical household has 30 light fixtures and uses lighting for 2,000 hours. When you replace all of the light fixtures from 100W incandescent bulbs to 30W compact fluorescent bulbs, you can save 4,200 kWh of electricity and about \$500 (when the average electricity price is 12 cents/kwh) in a year and still have the same amount of light. When you replace all of the light fixtures to 15W LED lamps, you can save 5,100 kWh of electricity and about \$612.

Note: The light output of a 100W incandescent bulb, 30W compact fluorescent bulb, and 15W LED lamps are all about 1,600 lumens.

### TEACHER GUIDE

The purpose of this activity is to enhance students’ skills in multiplication. To find out how much electricity the two types of light bulbs use for a day (PROBLEM A) or a year (PROBLEMS B), students will strengthen skills on multiply with multiples of 10.

#### Calculating electricity usage and electricity price

Math Skill: Multiplication

Using the amount of electricity usage of two types of light bulbs (regular light bulbs and energy saving light bulbs) for an hour,  students are asked to find out how much electricity they can save a day if they replace a light bulb with an energy saving one. Questions include, “Typically, we use lighting fixtures for 5 hours a day.  How much electricity do you use per day if you use a regular light bulb?”