Voltage drop problem. Transistor, optoisolator, relay for programmable Christmas lights?
Well, I managed to solve this by using a higher voltage, apparently 3 V wasn't enough to open the 2n2222 all the way, but 6V seemed to work, then a 47 ohm resistor to drive down the voltage (at 77 mA current I calculated that the resistance of the LEDs was about 40 ohm) to a level the lights could handle. This seemed to work.
Note that I have not hooked up a microcontroller at this point yet and basically this is more or less what I was trying to accomplish... probably I'll use a 9 V or somesuch DC source to drive the Arduino and use the same source to drive the LED's as well.