Visual introduction to LEDs
Todbot has a series of activities that introduce the arduino, leds, switches, etc.
Connecting LEDs and some answers to the way brightness may vary according to LED color, how they are connected, how many you use, the power supply, etc.
Instructables includes many creative explorations. This is a good "how to" resource that may inspire you to consider leds in new ways. Add to this your own artistic sensibilities while exploring seemingly simple but deeper questions about light and its relationship to human beings in general and to you personally.
one parts list