Added light sensor example

Author: tigoe

GA1AS202LightSensor/GA1AS202LightSensor.ino

@@ -0,0 +1,33 @@
+/*
+  GA1AS202 Light sensor
+
+   reads sensor on analog inout, outputs light value in lux
+
+   Slight rearrangement of  Bill Earl's example for Adafruit, 
+   with more notes.
+
+   This version assumes a 3.3V supply for the board, not 5V.
+   If you're using a 5V board, attach AREF to 3.3V and add this to setup:
+   analogReference(EXTERNAL);
+
+   modified 22 Jan 2016
+   by Tom Igoe
+ */
+ 
+void setup() {
+  Serial.begin(9600);   // initialize serial communication
+}
+
+void loop() {
+  // read the sensor:
+  int lightSensor = analogRead(A0);
+   /*
+     Top of sensor range is 100000 (10^5) lux.
+     (the 5.0 below is the exponent, NOT 5V)
+     Lux changes on a log10 scale, so you need to 
+     use the power (pow()) function to do the conversion:
+  */
+  float lux = lightSensor * 5.0 / 1024;
+  lux = pow(10, lux);
+  Serial.println(lux);
+}