The Collaborative International Dictionary of English v.0.48:

Lightsome \Light"some\ (l[imac]t"s[u^]m), a.
   1. Having light; lighted; not dark or gloomy; bright.
      [1913 Webster]

            White walls make rooms more lightsome than black.
                                                  --Bacon.
      [1913 Webster]

   2. Gay; airy; cheering; exhilarating.
      [1913 Webster]

            That lightsome affection of joy.      --Hooker.
      -- Light"some*ly, adv. -- Light"some*ness, n.
      [1913 Webster]

            Happiness may walk soberly in dark attire, as well
            as dance lightsomely in a gala dress. --Hawthorne.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lightsomely
    adv 1: moving with quick light steps; "she walked lightsomely
           down the long staircase" [syn: lightsomely,
           trippingly]
    2: in a light-hearted manner; "he light-heartedly overlooks some
       of the basic facts of life" [syn: light-heartedly,
       lightsomely]