The blocker is the opposite of the filter. Instead of blocking all about rather a purification does, it lets all about else pass & hinders lone a items specified.

E.g., an infrared blocker blocks out infrared weak, & lets obvious weak (among more wave lengths) pass across. An infrared purification bars a obvious weak & lets sole a infrared pass.

A term "blocker" is besides utilized around cell phone language. [http://www.cell-phone-jammers.com/cellular-phone-jammers.html]