for a 4x2x2 cab you could use a 250hps and supplimental cfl's . my main flower chamber was 4x2x6 and i used a 400hps and 4 42watt cfl's. it's gonna be tight with only 2' of height because the pot is gonna probably take up close to half the height leaving only 12-16" for the plant and lights. it's definetely possible you're just gonna have to find the shortest pot's with the largest volume possible. my brother has a cab that's only 26" tall so we cut a hole in the bottom for the pot to sit in so it doesn't take up any of the height. be creative!