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):

lightsome
    adj 1: moving easily and quickly; nimble; "the dancer was light
           and graceful"; "a lightsome buoyant step"; "walked with a
           light tripping step" [syn: light, lightsome,
           tripping]
    2: carefree and happy and lighthearted; "was loved for her
       blithe spirit"; "a merry blithesome nature"; "her
       lighthearted nature"; "trilling songs with a lightsome heart"
       [syn: blithe, blithesome, lighthearted, lightsome,
       light-hearted]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "lightsome":
   airy, blithe, breezy, buoyant, carefree, cheery, chirk, chirpy,
   chirrupy, clear, cloudless, corky, debonair, diaphanous,
   free and easy, insouciant, jaunty, light, lighthearted, lightish,
   lucent, lucid, luculent, pellucid, perky, relucent, resilient,
   serene, sunny, translucent, translucid, transparent, unclouded,
   unobscured