A: Our environment club is starting a "Lights-Out Lunch" next Monday. B: What do you mean by a "Lights-Out Lunch"? A: During lunch, each class turns off its lights and projector while the room is empty. B: I see. But what do you mean by "empty"? Some of us stay inside to study. A: Then those students can leave one row of lights on. Why don't you ask our class to join first? B: Sure. Why don't you put a short notice on each classroom door, too? A: Great idea. I'll design one tonight and print it tomorrow morning. B: Why don't you also count how many classes take part each week? I'll help you with the chart.

This graph uses made-up numbers. It shows how much electricity our school used each month from March to July. Electricity use stayed close to 30,000 kilowatt-hours from March to May. In June, however, it jumped to about 41,000, with air conditioners running in most classrooms all afternoon. After the student council recommended that every class keep its air conditioner at 26 degrees or higher, monthly use dropped to 36,000 in July. With the new rule followed in most rooms, the school saved about 5,000 kilowatt-hours in a single month. These numbers suggest that one simple rule can make a real difference. I therefore propose that the school post its monthly figures on the main bulletin board so that students and teachers can follow their progress together.