Well it depends... you'd have to find out if the officer wrote it down in his notes, and if not, if he remembers it at trial. As for admitting to an offence, R. v. Schlesinger
addresses this a bit. The defendant said he was "probably" speeding but did not say he was going as fast as the officer stated. He was found not guilty, but mostly because of some issues related to testing the speed-measuring device. The JP ruled that the defendant's admission that he may have been speeding was not enough to convict him.
BTW - did you specifically admit to going through a red light, or an amber light... or did you just admit to going through "a light"?