iOS 12
ENERGY STAR® compliance statement for iPad

To save energy, iPad is set to lock after two minutes of user inactivity. To change this setting, go to Settings > Display & Brightness > Auto-Lock, then select an option. To unlock models with the Home button, press the top button or the Home button. To unlock other models, tap the screen or press the top button.
iPad meets the ENERGY STAR guidelines for energy efficiency. Reducing energy consumption saves money and helps conserve valuable resources; see the Energy Star website.