"This lamp is already red."
Translation:Ez a lámpa már piros.
When ez and az function as demonstrative adjectives (as in, "this lamp" or "that doctor"), they need the definite article (a or az, depending on whether the next word starts with a vowel or consonant) immediately after them.
Ez a lámpa piros. (This lamp is red)
Az az orvos magas. (That doctor is tall)
Hol van az a paradicsom? (Where is that tomato?)