[youtube=http://www.youtube.com/watch?v=iEhX27ahreI&w=480&h=385]

This is how to make a simple light tracker/follower with the Arduino. The components you need apart from the Arduino is:

2x Photoresistors: “PHOTOCELL2 Miniature Photocell”.
2x 470 Ohms resistors.
1x Servo.

And of course some wires, and a breadboard or two :). Next step is to wire it all up, I’ve made a drawing in Fritzing that you can follow. Basically each photoresistor is wired likes this:

PhotoR       470Ohms
+5    o—///–.–///—o GND
|
Pin 0 & 1 o——-

Program Code:

#include <Servo.h>

Servo myservo;

int pos = 0;  // Variable to store the servo position.
int inputPhotoLeft = 1; // Easier to read, instead of just 1 or 0.
int inputPhotoRight = 0;

int Left = 0; // Store readings from the photoresistors.
int Right = 0; // Store readings from the photoresistors.

void setup()
{
myservo.attach(9); // Attach servo to pin 9.
}

void loop()
{
// Reads the values from the photoresistors to the Left and Right variables.
Left = analogRead(inputPhotoLeft);
Right = analogRead(inputPhotoRight);

// Checks if right is greater than left, if so move to right.
if (Left > (Right +20))
// +20 is the deadzone, so it wont jiggle back and forth.
{
if (pos < 179)
pos++;
myservo.write(pos);
}

// Checks if left is greater than right, if so move to left.
if (Right > (Left +20))
// +20 is the deadzone, so it wont jiggle back and forth.
{
if (pos > 1)
pos -= 1;
myservo.write(pos);
}

// Added some delay, increase or decrease if you want less or more speed.
delay(10);
}

PS. If you got any questions etc, please take it in my forums post here.