light sensing off and on 5 m white LED strip

Hi,

I’m new to Arduino and electronics and I’m trying to make a lighting system that goes on when it senses light (it is for inside a wardrobe).

I’ve made a simple proof of concept with a simple LED and now i’m moving on to the LED strip and external power supply.

So I’ve got
12 V DC 3 A power supply
Arduino Uno
Breadboard
5 M LED strip

link for pic https://dl.dropboxusercontent.com/u/35749900/WP_000782.jpg

The lights work when connected through the breadboard directly to power supply but not when I try to adapt my set up that worked with the LED. On the picture the power goes in at the top right, LED bottom right. There’s a TIP120 transistor in there too. In fact, I tried to base it on this http://blog.dcxn.com/2013/03/03/dimming-a-12v-led-strip-with-an-arduino/

Any ideas whee I’m going wrong as it’s no longer lighting with this set up

Here’s the code I’m running

int sensePin = 0;
int led = 9;
int brightness = 0;
int fadeAmount = 0;

void setup()
{
  analogReference(DEFAULT);//isn't necessary
  pinMode(led,OUTPUT);
}
void loop()
{
  int val = analogRead(sensePin);
  if (val > 350) 
  {
    if(brightness != 255) 
    {
      brightness = 0;
      for(brightness = 0; brightness <= 255; brightness += 5)
      {
        analogWrite(led,brightness);
        delay(50);
      }
      brightness = 255;
      analogWrite(led,brightness);
    }
  }
  else 
  {
    brightness = 0;
    analogWrite(led,brightness);
  }
}