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Difficulty: MediumExplaining Surprising Outcomes

To reduce its environmental footprint, a corporate office replaced all manual light switches with motion-sensor switches designed to turn lights off whenever a room is unoccupied. The building's occupancy rate, operating hours, and total number of light fixtures remained completely unchanged. Yet, one year after the installation, the building's total electricity consumption specifically for lighting had increased by 15% compared to the previous year.

Which of the following, if true, most helps to resolve the apparent paradox?

  1. A
    Due to a rate hike by the local utility provider, the monetary cost of electricity per kilowatt-hour increased significantly during the year after the sensors were installed.
  2. B
    The motion sensors are programmed to turn the lights off within three minutes of a room being vacated, whereas employees previously often left manual switches on for several hours.
  3. The motion sensors automatically activate the lights at their maximum wattage upon detecting movement, whereas employees using the manual switches typically kept their office lights heavily dimmed.Answer
  4. D
    Studies show that offices with automated lighting systems tend to have higher overall electricity usage, though researchers have not determined if the lighting systems are the direct cause.
  5. E
    Although the total electricity consumed by lighting increased, lighting now accounts for a smaller percentage of the building's overall energy consumption than it did last year.

Answer

The statement that the motion sensors automatically activate the lights at their maximum wattage, whereas employees previously kept their lights heavily dimmed.
This option successfully resolves the discrepancy by introducing a new variable: light intensity (wattage). Even if the motion sensors reduce the total amount of time the lights are left on, automatically activating them at their maximum wattage uses significantly more electricity per minute than the heavily dimmed lights used previously. This higher rate of continuous consumption easily accounts for the 15% overall increase in electricity usage.

Step-by-Step Solution

1
Analyze the apparent discrepancy presented in the stimulus.
The company installed motion sensors to turn off unoccupied lights, aiming to save energy. All other factors (occupancy, hours, fixtures) remained constant, yet lighting electricity consumption increased by 15%.
Understanding the exact parameters of the paradox is necessary to identify what kind of new information can bridge the gap.
2
Determine the requirements for a successful resolution.
The correct answer must provide a reason why the new sensors cause more electricity to be drawn when they are on, outweighing the energy saved when they turn lights off.
Since the time the lights are on has presumably decreased (or at least not increased), the rate of energy consumption while on must have increased to result in a net gain.
3
Evaluate the options against these requirements.
The option regarding maximum wattage provides the exact mechanism needed: higher intensity (wattage) uses more electricity than dimmed lights, fully explaining the absolute increase in consumption.
This is the only option that addresses the actual rate of electricity consumption rather than cost, outside correlations, or irrelevant percentages.

Key Concept

Resolving a Paradox by Identifying Counteracting Variables
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Topics

Explaining Surprising Outcomes

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