In message , at
01:21:00 on Mon, 31 Oct 2005, Colin Rosenstiel
remarked:
TBH, not being an Oyster user I hadn't even noticed. My attention has
always been on the bit relevant to me. As has been explained to you, the
red light doesn't mean go, it means the Oyster reader is not ready to
read Oyster cards.

That may be the technical explanation (and it came up in here years ago
when the Oyster attachments were first installed), but for a normal
person who is simply using the gates, they get a consistent indication
that "red means ticket is OK".
--
Roland Perry