Moist_Plasma:
it would be more easily accomplished by simply using two Light Dependent Resistors (LDR)s facing in the forward direction and one slightly turned to the left and the other to the right. Then telling it to turn towards the brighter side until the light hitting the both LDRs was equal. BUT that's not what we are going to be doing!
Thinking some more about this ...
My feeling is that the task of facing towards the brightest light in the room is too simple to provide a basis for developing a neural network example program.
I think you need to conceive of a problem that cannot be solved with a pair of LDRs and simple "point-me-at-the-light" code because then you will be faced with a real learning challenge (both you and the robot).
If you think about it, if you already had a complex functioning neural network and presented it with the "find a light" problem it would very quickly reduce itself to the two-LDR solution. Otherwise it would be a pretty crap neural network.
...R
Edited to add the words in green - see Reply #12 below