Selco not only discusses the importance of having light in a SHTF scenario, but also the importance of darkness on his blog. Read it.
Have light appropriate for your situation.
Load up on rechargeable batteries and solar battery chargers.
Don't forget the tea lights and disposable lighters which can double as bartering objects.
In most situations, do not use a light outside at night. Practice using your natural night vision, as Selco recommends and as Matt Bracken has written about.