Well OP, firstly lemme say that I don't believe that there is in actuality a real bet - I'm guessing that you only have $200 for lights, already have some fluoros, and in a big dream in your head think that you can get a pound off of them (which, coincidentally, is about $4000 worth of weed most places).
That being said, if I'm wrong and there really is a bet (in which case I apologize for doubting you, but I'm pretty sure that I'm right), I'd think long and hard about what words were used between you and your friend when making the bet - your post simply says "harvest a pound", not "harvest quality, smoke-able nugs", in which case you could probably just grow a few plants under fluoros, and when the time came, chop down a couple of whole plants and give them to him and receive your $4000.
BTW, what exactly do you lose if you can't grow a pound under fluoros in five months? Because to make it a bet you'd have to have something at risk (which I guess could be your time, but usually people attach a monetary figure to said risk).
And why would your buddy pay you $4000 for the undoubtedly not-so-great weed that fluoros produce?
I'm calling BS, but best of luck to you.