between certain times of the day, when its quiet, some traffic lights go into auto mode. they are triggered by headlamps, pressure sensors or the metal in car bodies via magnetic strips in the road ( its those criss cross bitumen lines on the road near traffic lights).
unfortunatly, bikes are too light and don't have enough metal to trigger the signals. I'm sure I read somewhere you are entitled, after so many mins, to ride through lights if they are faulty.
I had to do that on a right turn coz I'd been there 10 mins!! i pushed the bike across the junction
you can buy a magnet that fits under your bike to energise the sensors. give the lights a flash as well, those sensors are on top of the lights themselves
drewps