My better half just returned from a holiday with her sister and brought me back a brochure from Oahu Ghost Tours (and an iPad! but that's another story).

One of their tours is called Orbs of Oahu. 

from the brochure….  "Can you explain the fireballs that appear out of nowhere?  And, oh yeah, Night Marchers.  Should we stand in their path?  Please don't look directly into their eyes.  It means certain death!

Catching a ghost on film isn't as hard as you think!  A camera is an effective tool to get hard evidence that ghosts do exist.  One thing to remember though; ghosts most often appear as orbs, balls of light, or mists.  Do not get discouraged if you don't get a human-like form in your pictures.  The orbs are just as good."

their website:- http://www.oahughosttours.com/

one of the 'ghosts' on their site. sigh.