Describir: Light as a transient medium

 _    _    __   __    ______     ___      _____    _    _     ____    
| || | ||  \ \\/ //  /_____//   / _ \\   / ____|| | || | ||  |  _ \\  
| || | ||   \ ` //   `____ `   | / \ || / //---`' | || | ||  | |_| || 
| \\_/ ||    | ||    /___//    | \_/ || \ \\___   | \\_/ ||  | .  //  
 \____//     |_||    `__ `      \___//   \_____||  \____//   |_|\_\\  
  `---`      `-`'    /_//       `---`     `----`    `---`    `-` --`  
                     `-`                                              
 _    _   
| || | || 
| || | || 
| \\_/ || 
 \____//  
  `---`