Stray Capacitance in my load waveform?
My first guess would be inductive pick-up in your scope probe.

Try to make the GND loop connection from your scope probe to your board smaller in area (it's all about area for inductive pick-up) - keep it as close as possible to the side of the scope probe. Also try tightly twisting the leads to the bulb if they are, as you said, quite long. 

Hopefully what you are seeing are measurement artefacts and, if so, should be reduced with the techniques described.