Energy and lighting lights

I know, not the best title ever. I’ve seen exhibits where someone pedals a bike and the more energy they produce the more lights that come on. It is sequential so you start with one light, two, three, etc. My question is how is the light board wired to have the lights behave that way.

One simple way is to wire the lamps/bulbs in parallel. Next, insert resistors of increasing values in series with each lamp/bulb. The voltage across each successive lamp will be reduced and so the pedaler will need to produce higher voltage to get those lamps to light up.