Light is an amazing source of energy—the power behind virtually everything that happens on Earth. Light from the Sun brightens the dark depths of space, makes plants leap to life, and (indirectly) powers our bodies. But did you know it can help to clean things as well? By using a method called photocatalysis, light energy kick-starts a process that zaps all kinds of nasty air pollutants and turns them into harmless substances instead. For people who suffer from asthma and allergies, light-powered air purifiers like these are another weapon in the fight for cleaner air and better health. Now photocatalysis might sound horribly complicated, but it works in a relatively simple way.