U.S. Patent No. 6,596,981, directed to ambient light sensors.

The default mode of operation of the accused product does not infringe (page 38).  The infringing mode was not shown to be used, so there is no infringement of the method claims (page 39).  The system claims require devices capable of performing an act (“means . . . for determining”), so are infringed (page 39).

Hindsight: It may be helpful to use both system and method claims.  That diversity in claiming may save the day.