That would be a piece of cake to do with a single NPN transistor. A 2N2222 can safely switch up to 500mA without a heatsink, but if your lamps are incandescent, you'll need a bigger transistor than that. Your lamps, when cold, can pull up to 1.5A for several milliseconds. You'd do well with Darlington power transistor, like a TIP29.http://www.mouser.com/ProductDetail/Fai ... 6%2fv5c%3d
Do not ignore the incandescent surge phenomenon. Leave yourself a safety factor of at least 10x (yes, that's right- ten times the hot current) when specifying any kind of switching device for such lamps. Many a newbie (and even a few folks that should know better) have been burned by this!
If you want to support this great site, you can also use a power MOSFET like this one:http://www.adafruit.com/products/355
It's way overkill for your application, but you can always use it for something else, including switching on lots and lots of lights!
Just wire it up per the usual tutorials. You will need:
A TIP29 transistor (or N-Channel MOSFET)
a 1/4 Watt resistor, 4.7K for a TIP29 (Optional for a MOSFET, but if used, value should be less than 220 ohms)
A. Connect the Positive terminal of the Wall Wart to one side of the lamp
B. Connect the other side of the lamp to the Collector (Drain) terminal of the transistor
C. Connect Base (Gate) terminal of the transistor to one end of the resistor
D. Connect the other end of the resistor to a digital output
E. Connect the emitter (Source) terminal of the transistor, the Negative terminal of the wall-wart and at least one Arduino GND terminal all together.
(By the way- if you use the analogWrite(pin, n) command on a PWM output, you can dim the lamp any way you want, or ramp the brightness up and down slowly or quickly, etc.) where 0<n<255
Caution- many LV lights use 12V AC. Make absolutely sure you have a DC wall wart! The above circuit won't work on AC