We approached this end-of-the-year assignment with the idea that we wanted to do an experiment that would further investigate the personal applications – that affect us directly – of some of the issues we learned about in this course. From nuclear crises to car fuel efficiency, what stuck with us most is how we all affect global warming, and how it affects us all.
What better than light bulbs? Lighting is about 20% of the average household’s electric bill: they are a necessity in our daily lives, lighting everything from our homes, classrooms, even transportation. We wanted to test the efficiency of an object that is so relied on by our society, and to see if what is marketed as energy efficient bulbs are worth the hype and extra money.
The most commonly used energy efficient bulbs are Compact Fluorescent Lamps, or CFLs. They last between 8 and 15 times longer than average incandescent light bulbs, and use almost 75% less electricity. Incandescent bulbs light when an electric current is run through a wire filament, heating the filament until it glows. CFLs alternately run an electric current through a tube containing argon and a small amount of mercury, generating ultraviolet light that activates the fluorescent coating on the inside of the tube. CFLs run much cooler than incandescent lamps, significantly reducing the heat due to lighting. This is especially beneficial in warmer climates, lightening the load on your houses’s cooling system.
This chart demonstrates the energy use for different types of bulbs, comparing lumens (light) to electrical consumption. The top line is incandescent bulbs, and the bottom is CFLs.
Our initial thought for conducting this experiment was using two bulbs, one incandescent and one energy efficient, and measuring the heat that came off of them over a period of time. This would show us the energy that is wasted in excess as heat. After consulting with Professor Sonek, who pointed out that this was not complex enough and we needed more factors to measure, we revised the experiment to calculate the efficiency of each bulb by using the Lego Mindstorm program to measure lumens emitted, as well as measuring their heat, voltage, and electricity. Those numbers would be plugged into the equation
efficiency = output (light + power in heat) / input (electrical, i.e. voltage x current)
Following another meeting with Professor Sonek, our experiment underwent another (final) revision. Using a solar cell to measure the amount of light and resistance emitting from, as well as the amount of watts going into, each light bulb. however using the solar cell, only a portion of the total area of light gets a reading. We therefore had to use the following equation to get a reading for the whole surface:
area of hemisphere (lamp) = 2 r squared
power of the cell (resistance) = V/I = voltage/current
*note: in most materials, V and I are directly proportional: therefore resistance, or power, are constant.
Materials: lamp, ruler, incandescent light bulb, compact fluorescent light bulb, and solar cell.
Use the lamp to alternately screw in the appropriate light bulb. Measure 5 cm from the light bulb to place the solar cell. (Before using the solar cell, first measure the area of the solar cell.) Record the cell voltage cross a 25 ohm resister. Record the wattage of each bulb, and the amount of light emitted – using the same distance (5 cm) for both.
After collecting the date for both bulbs, plug the results into the following efficiency equation:
Efficiency = (Area of Hemisphere/Distance from Bulb) x (Power of Cell/Power of Bulb)
(160/14)X(31/150)=82
Which bulb used the energy most efficiently?
Looking at the results, as a class we concluded that the energy saver was the most efficient choice of light bulbs.
When trying to help the other student groups in class through this experiment, we found that while they understood the concept and purpose of our experiment (to test the efficiency of light bulbs), we found that the calculations and math were complex and difficult.
