
Quoting
Mr. Knowitall
The law in Pennsylvania was summarized in the following case. (I don't see that the law has changed appreciably since that time but you should always check for more recent judicial opinions.)
Liability would thus appear to turn on the extent to which you reasonably relied upon the lighting to deter crime and whether you can show a causal connection between the landlord's failure to maintain the lighting and the occurrence of the crime under discussion. That does not sound like an easy case to make in court, but if the landlord is willing to voluntarily take responsibility you won't need to do so.