The word lightproofer is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 23
Highest Scoring Words With Friends™ Play In The Letters lightproofer
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Seven Letter Word Alert: (30 words)
egotrip, fighter, firepot, flirter, forgoer, freight, froglet, frother, goofier, goopier, hoplite, lighter, loftier, loopier, petifog, philter, philtre, politer, poofier, pothole, profile, proofer, relight, repilot, reproof, righter, trefoil, trifler, tripole, trooper