After careful examination of our data, it can be concluded that increasing screen brightness does increase the power consumption of a laptop. However, while we hypothesized that changing the brightness would increase power consumption by a consistent ratio, we found no such consistency. In our data, we calculated that increasing brightness from 25%-100% increased wattage consumption by an average of 26%, but there were great deviations within this percentage. This was calculated by subtracting the wattage consumption at 25% brightness from the wattage consumption at 100% brightness, and dividing that number by the max wattage consumption.

Example Calculation for MacBook Pro (mid-2012, 15 inch w/ Retina Display):

18.5W-11.2W = 7.3W/18.5W= 39% decrease in power usage.

All the calculations were averaged together to receive a value of 26%.

This inconsistency may be due to several possible sources of error, including the running of background programs that we were unaware of, which could create a second variable affecting the recorded power values. Another possible source of error is equipment failure (as observed in Tori’s data but to a lesser, less noticeable degree). Our results show that, while decreasing the screen brightness of a laptop may decrease the power output of the computer, the decrease is slight and inconsistent.

The science we learned during our experiment included a fuller understanding of the scientific method, data collection methods, and data analysis through graphs. We also gained a better understanding of the relationships between voltage, current, and power, including V=IR (Ohm’s law) and P=IV.

If we conducted this project again, we would try to take more data points from many more laptops to create a broader relationship between screen brightness and power output. We would make more of an effort to control for accidental variables, like background programs. We would also start our research earlier, to give ourselves more time to collect more data and analyze it more thoroughly using LoggerPro.

If we were to conduct our research for 6 more weeks we would take data from many, many more laptops and we would expand our research to include laptops of other brands, like Toshiba and Sony, instead of limiting ourselves to only Apple laptops. We could also expand our data collection techniques to include other screen brightness levels, instead of only taking data at 4 different brightness levels. If we had more time, we would also closely examine the laptops with high power output to see if they were infected with viruses. This would provide a bigger picture of the relationship between screen brightness and power output.

We graphed the output of power, current, and voltage for each laptop computer we received data from. We excluded all zero values, as we attribute those recorded values to a malfunction in the Watts Up Pro or human error while recording data. We can see from our graphs that power and current increase, if only slightly, when the screen brightness is increased. The voltage, however, does not seem to change much and does not have an overall trend of increasing or decreasing when the screen brightness was changed.

Roles:

Each member of the group will collect the same amount of data. We will each analyze 7 Apple Brand laptops. The laptops we examine will be MacBooks, MacBook Pros and MacBook Airs from 2008 onward. We will then all work together to analyze the collected data through the use of graphs. From our analysis we will collectively write a conclusion explaining our results.

List of Equipment and Supplies:

• WattsUp? Pro (3)

• Apple Laptops (21)

Science and Technology:

Through the use of the WattsUp? Pro, we will determine the the power usage of different laptops using different brightness configurations. Since power=energy/time, we will determine how much energy the laptops use of a period of one hour by using the WattsUp? Pro’s energy measuring capabilities. This information is extremely applicable to daily life because it can be used to calculate how much it will cost to run a laptop on different brightness levels, as well as how rapidly the laptop’s battery will be exhausted based on its brightness. This can help users decide how much battery they can actually save by lowering brightness and adjust the brightness levels to their needs.

Activity Plan:

The first part of our project will be to collect the data about the laptops’ screen brightness. Each member of the group will collect the same amount of data using the WattsUp? Pro. We will each record the power usage of Apple Laptops, including MacBook Pros and Airs of different models, at approximately 25%, 50%, 75%, and 100% brightness and then combine our data into one aggregate. We will collect our data during the week of 9/23-9/28, and then meet the following week (9/30-10/5) to combine and analyze our data. We will finalize our project and draw conclusions from our analysis during the week of 10/7.

Expected Outcomes:

We expect that lowering the brightness of the screen will significantly decrease the battery consumption on every laptop that we test. We anticipate that lowering the brightness will decrease battery consumption at a consistent ratio.

Our group will perform data collection using the WattsUpPro device to determine the battery usage of different laptops at different screen brightness levels. We will use the laptops of our peers to get a sampling of a variety of different models of MacBook laptops, since this is the most widely used laptop on campus. Our goal is to determine how much changing the brightness level actually effects battery consumption and if it is worth it to lower brightness and cause unwanted eye strain.We expect that lowering the brightness will decrease battery consumption at a consistent ratio. We want to determine how much different screen brightness levels actually affect how quickly a laptop battery will die.

Meow

Molly Osborn, September 12, 2013

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