The Collaborative International Dictionary of English v.0.48:

Dim \Dim\, v. t. [imp. & p. p. Dimmed; p. pr. & vb. n.
   Dimming.]
   1. To render dim, obscure, or dark; to make less bright or
      distinct; to take away the luster of; to darken; to dull;
      to obscure; to eclipse.
      [1913 Webster]

            A king among his courtiers, who dims all his
            attendants.                           --Dryden.
      [1913 Webster]

            Now set the sun, and twilight dimmed the ways.
                                                  --Cowper.
      [1913 Webster]

   2. To deprive of distinct vision; to hinder from seeing
      clearly, either by dazzling or clouding the eyes; to
      darken the senses or understanding of.
      [1913 Webster]

            Her starry eyes were dimmed with streaming tears.
                                                  --C. Pitt.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dimmed
    adj 1: made dim or less bright; "the dimmed houselights brought
           a hush of anticipation"; "dimmed headlights"; "we like
           dimmed lights when we have dinner" [syn: dimmed, dim]
           [ant: bright, undimmed]