Hi,
CGA starts on a shape and has no information about neighbors what so ever. This is a limitation of CGA currently. The only exception is occlusion queries ( see docs ), but those cannot query any other specific parameters of neighbors.
The only way you can do this currently is using Python to inform your buildings that they touch each other and have a combined length of 60.
E.g. also use these steps:
Model Generation 1 : create no lights, but create reports
Python: Evaluate reports and write attribute data ( e.g. 'is big building, thus add lights on top' )
Model Generation 2: pick up attribute, generate lights !
e.g. if you have an attribute called 'wasGeneratedAlready = 0', you know in CGA that you don't want to add lights but report. After Python wrote the attr as 1, you create the lights.
[Note that all those 3 steps can be combined in 1 Python script, if needed. You'd be using the script based exporter in this workflow.]