6) Use it!
The light level is now being transmitted from your XBee Gateway! Place it in some sunshine and see if you get the widget to show 100% as the sensor saturates with brightness. Cover it with a box to see it go towards 0%. You can also add a graph widget to examine the brightness data over time. See if you can sense cloudy periods, or watch the sunset data in real time. You can also run your setup from a battery pack and place it in your refrigerator. When the door is closed, does the light really go out? You might want to try setting up an Alarm in Device Cloud to alert you to late-night snackers.
There are many different light sensors available, all with different ranges and response characteristics. Most light sensors will generate data that changes very quickly. If you want to experiment with slowly changing sensor data try building the temperature sensor.