NAME
	  DtLightIsValid - Get the state of the	valid bits for the
	  given	light.


     SYNOPSIS
	  #include <Dt.h>


	  int  DtLightIsValid( int lightID, int	valid_bit )


     DESCRIPTION
	  DtLightIsValid() returns 1 if	none of	the attributes of a
	  light	indicated by lgihtID have changed for the current
	  frame, otherwise it returns 0.  The valid_bit	parameter is
	  used to check	if any or all attributes of the	light have
	  changed.  The	following attributes can be checked to see if
	  they have change from	the previous frame:

	  DT_LIGHT - any of the	attributes below have changed.
	  DT_LIGHT_ON -	light status (on or off) has changed.
	  DT_LIGHT_INTENSITY - intensity has changed.
	  DT_LIGHT_COLOR - color has changed.
	  DT_LIGHT_POSITION - position has changed.
	  DT_LIGHT_DIRECTION - orientation has changed.
	  DT_LIGHT_DROP_OFF_RATE - drop	off rate has changed.
	  DT_LIGHT_CUT_OFF_ANGLE - cut off angle has changed.


     FILES
	  Link with -lDtOMio