How to Build Sequential Lamp Tree for Treadmill Motor Bicycle Generator Classroom Project

So, to start off I am not an electrical engineer, I am a master electrician that teaches at a career and technical high school. we are working on a project where  we salvaged a motor from a Tread mill and have coupled it to a bicycle.  I would like to be able to build a "Tree" of lamps in such a fashion that they would light up sequentially as more voltage is applied.  (Like a carnival game the students can "race" to see who can light up the most). 

I am looking for advice or guidance of what I would need to frugally accomplish such as this was not in my budget and I will be paying for this out of pocket.
Thank you in advance!  

Ryan... can you advise... is your generator putting out DC or AC?  I'm assuming DC? and what voltage?
To keep it simple, you can use a Zener diode with a resistor going to the base of a power transistor, with the collector driving a lamp.  By making a few of these circuits with different voltages of Zener diode, you can get lights to come on at different voltages.It'd difficult for us to post diagrams here but if you advise more specifics I can suggest more detailed solutions.

Yes it a DC motor,  originally  operated at 95 volts but I'm estimating  it to produce in the vicinity of 18 volts with how fast they have been able to spin it.  We are still constructing the frame and as soon as we put it together we can have an actual voltage output.  

I think the trick to keeping it really simple would be to NOT try to power the lights from the generator. Put a load across the generator (so some actual work will be involved), then if it's an AC generator(alternator), add a rectifier, and feed the resulting output into an analog bar graph display.  If you do an internet search you'll find tons of ways to build an analog bar graph display.   
Another possibility would be rather than having multiple lights, find a big analog panel meter and use that as the display. Super easy!  If you have trouble finding a big analog meter, try searching for a local Hamfest.  Hamfests are get-togethers for Amateur Radio Operators, and they always have tons of odd parts for sale (also lots of free advice!)-Rick 

Rick and David have already given some good suggestions. The only thing that I would add is that you could also use a Voltmeter display (either digital or analog)  You could use a resistor divider if necessary to scale the output.

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Thanks for sharing Matt

thanks