There was talk years ago, about using the part of the high tension voltage from the field collapse of the magneto's coil: inductively coupled to a capacitor, or another transformer, or both, to use the same as the spark plug. This was before White Light Emitting Diodes appeared on the market. They figured there still wouldn't be enough current generated from the scheme, to illuminate a 20 W 12V incandescent bulb to a desirable enough candlepower, up to and including it's rated output.
But since WHITE LED devices are available to the engineers, and consumers, as well, It could very well be feasible to generate enough light, just by induction coming from the field collapse (fly-back) from the magneto, with the scheme mentioned above; It would mean: No batteries required, self contained, and reliable.
If interested, We might be able to experiment and with tech support from engineering websites, we may be able to come up with a working prototype.