Which is correct-p
PLEASE ENSURE THE LIGHT IS GREEN or PLEASE ENSURE THAT THE LIGHT IS GREEN.
Barry
Both are correct. The subordinator "that" is sometimes obligatory, sometimes optional, and sometimes inadmissible.
OBLIGATORY: That I need help is clear. *I need help is clear.
INADMISSIBLE: I left before he arrived. *I left before that he arrived.
OPTIONAL: I know that it's genuine. I know it's genuine.
* = ungrammatical
Generally, "that" is optional, though it is more like to be omitted in informal than in formal style, and it is more likely to be omitted after short and common verbs than after longer and less frequent ones. For example, in "This will demonstrate that it is genuine", the subordinator would probably not be omitted.