Which of the following actions contributes to energy conservation?

Turning off lights when leaving a room is a crucial action that contributes to energy conservation. This practice reduces unnecessary energy consumption by ensuring that lights are not left on when they are not needed, effectively cutting down on wasted electricity. Since lighting accounts for a substantial portion of energy use in homes, this simple yet effective habit can lead to significant energy savings over time.

In contrast, using high-energy appliances can lead to increased energy usage and costs, as they consume more power than energy-efficient alternatives. Leaving devices plugged in contributes to what is known as "phantom load," where appliances draw power even when they are turned off but still plugged in. This results in unnecessary energy consumption. Lastly, using outdoor lighting all night can lead to excessive energy use, particularly if the lighting is unnecessary during certain hours when natural light suffices. Hence, turning off lights when leaving a room stands out as a direct and simple method for conserving energy effectively.