Merriam-Webster Collegiate Dictionary - lightness

 I. noun  Date: before 12th century  1. the quality or state of being illuminated ; illumination  2. the attribute of object colors by which the object appears to reflect or transmit more or less of the incident light — compare brightness 2, hue 2c, saturation 4  II. noun  Date: 12th century  1. the quality or state of being light especially in weight  2. lack of seriousness and stability of character often accompanied by casual heedlessness  3.  a. the quality or state of being nimble  b. an ease and gaiety of style or manner  4. a lack of weightiness or force ; delicacy