Landing lights are usually extinguished in cruise flight, especially if atmospheric conditions are likely to make the lights reflect or glare back into the eyes of the pilots. However, the brightness of landing lights makes them useful for increasing the visibility of an aircraft to other pilots, and so pilots are often encouraged to keep their landing lights on while below certain altitudes or in crowded airspace. Some aircraft (especially business jets) have lights that— when not needed to directly illuminate the ground—can operate in a flashing mode to enhance visibility to other aircraft.