From the NannyMUD documentation

LAST CHANGE

2001-08-12

FUNCTION

NAME
        dark - Make a room dark regardless of light level.


LOCATION
	In rooms that may be entered by livings.

SYNTAX
	int dark(string condition, int brief_mode);

DESCRIPTION
	condition can currently only be "move_player" if called from
	real_move_player() in /obj/living_functions.c or 0 if called
	for commands like "look".
	brief_mode is true if player is in brief mode. Use this to
	modify  your texts.

	A return value of true means don't print _anything_; any text
	written will be written by the dark() function.


EXAMPLE
	inherit "/std/basic_room";
	 
	reset(int arg)
	{
	  ::reset(arg);
	  if (arg)
	    return;
	  set_short("testroom");
	  set_long("Testing room.\n");
	}
	 
	int dark(string condition, int brief_mode)
	{
	  if (condition=="move_player")
	    if (brief_mode)
	      write("Complete darkness.\n");
	    else
	      write("You enter a completely dark place where lamps "+
	            "does not help.\n");
	  else
	    write("It is so dark in here that no light can "+
		  "penetrate the darkness.\n");
	  return 1;
	}