WordNet (r) 3.0 (2006):

lightproof
    adj 1: not penetrable by light; "lightproof containers" [syn:
           lightproof, light-tight]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "lightproof":
   airtight, close, compact, dustproof, dusttight, fast, firm,
   gasproof, gastight, hermetic, hermetically sealed, lighttight,
   oilproof, oiltight, rainproof, raintight, sealed, shut fast,
   smokeproof, smoketight, snug, staunch, stormproof, stormtight,
   tight, water-repellant, waterproof, watertight, windproof,
   windtight