Setlight (string)

   Synopsis:
      Sets the world model's light status

   Notes:
      The rooms in the world model can have several stored descriptions, each
         corresponding to a different light level (the default light status
         strings are "day", "night" and "dark".)
      This function changes the current light status. To get the current light
         status, see the Getlight$ () function.
      Returns 1 if the light status is set, or 0 if the operation fails.
