"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?)
There is a very good reason. "Ez lámpa" is taken, it means something else. It means "This is a lamp". So, "This lamp" has no choice but be "Ez a lámpa". :)
So putting the verb "van" in the end is actually an error and not optional?
"Ez a lámpa már vörös" was not accepted.Any particular reason for this?
"vörös" and "piros" are probably not interchangeable. Why, I do not know - but would like to. Maybe different hues of red, like scarlet (bright red) and crimson (deep red)? Or maybe "vörös" is more for blood, as in "Vörösmarty Tér" in Budapest.
It dependa on the color of red. Vörös is usually a darker res, while piros is a bright red. Red wine is vörös, street lights are piros.
In this case, I would think either shiuld be acceptable, because we don't know.