Help check my Noob math

Alright, hopefully this will be the last plea for assistance, I just want to check my math before I pull the trigger.

In building a prototype of the wall sconces, I need to figure out just how much light is appropriate. So I reason a constant voltage driver will allow me to vary current across the one LED I'm running with use of various resistors and find a happy amount of lumens.

My question is thus: what numbers should I be looking for in a driver to run a single Rebel between 100ma-700ma.

Assumptions (prob wrong):
output Voltage 12v (constant)
output Current: .1a-1a
output power: ???W
Input voltage: 120VAC

(specific driver suggestions always welcome)
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Assuming some form of the above driver, If I wanted to run the Rebel at 350ma for example. would I simply hook up the driver, Rebel, and a 27 ohm resistor in series? ( http://led.linear1.org/1led.wiz?VS=12;VF=3.2;ID=350 ). I apologize for my simplistic questions, but I really hit a brick wall when it comes to the technical stuff.

Thanks

What math? I don't see anything you attempted to solve.

12 volt supply for one LED is a waste of electricity. The LED will drop around 3.5 volts and leaves 8.5 volts that has to be dropped by the resistor(s). Since the current is the same in each device of a series circuit, the resistor is dissipating over twice the energy of the LED.

Much better to put three LEDs in series and drop the rest through the appropriate sized resistor or use an efficient switching regulator.

The output of a 12volt supply with .1 to 1 amp current is 1.2 to 12 watts. Simply multiply the voltage by current to get answer. So, at 1 amp, the LED dissipates 3.5 watts and the resistor, 8.5 watts!

However...
A simple 12 volt PSU will deliver 17 volts at no current and and gradually less as current increases. At .1 amp a 1am 12volt PSU will still be up around 15 volts. Ignore this if your PSU is regulated.

In a continuous light source, I'd underdrive the LEDs for long lifetime. Do not consider overdriving in this application. For example. the Cree XR-E is projected to last 50K hours at 700ma for 25% loss in output (IIRC). I would heat sink them well and not drive them past 500ma for a long lasting, reliable product.

Lets say your PSU is regulated at 12 volts and you still want to use one LED and 700ma. I'll assume the LED drops 3.5 volts, so we need to find a resistor value to pass .7 amp at 8.5 volts. 8.5v divided by .7a = 12.1. So a 12 Ohm resistor is close enough. (E/I=R)
Resistor needs to dissapate about 6 watts so you need a big ceramic one!