Possible Clues:

• Absence of light
• Lack of light
• Ask nerds - somehow this will never see the light of day?
• Gloom
• 'Hello . . . . . . . ., my old friend' (Simon and Garfunkel song)
• This always is at the end of the day nigh to tea
• No light
• Unlit state
• '... cannot drive out ...: only light can do that'' (Martin Luther King)
• Rescue boat trapped between delta and cape in night-time