== Ws or Joule is a unit used in photography to describe the energy stored in the capacitors of the flash circuit. == 

 The article incorrectly states the Watt second is used in photography as the energy stored in the flash tubes.  It is actually stored in capacitors in the power pack portion of the system.  The flash tube is also rated in Watt seconds, not as a unit of storage, but as a specification of the maximum energy it can handle without damage.  The flash tube provides a place for the energy stored in the capacitors to be converted to energy as light, or lumens. 

    Photographer EE, July 15, 2014