I lane spilt regularly on a bike. If only so I don't have to overtake later but...
If the light was about to change to green it was the wrong time to be doing it.
Giving it to you straight here, it sounds like your attention was more on the light than on where you were - which is not cool in a lane split.
Sooooooooo the lesson for today is. If you have any doubts about doing it, if you don't have the time to take care and concentrate on where you are and what you are doing then don't.
It's a simple rule that applies to most things on a bike. Every so often there will be a time you won't be able to and thats when things are more likely to go wrong.
My instructor was hounding me before my test to slow down and give myself time to do what I needed to, rather than keep the speed I had and take chances. Thing is, and I don't like admitting it - he was not only right, he is the reason I have a full licence.
Britjoe: I feel your pain, I can't lane split on the CX (well I could but it'd get real messy) and it's killing me!