Patent ID: 8336543

Claim:
A filter cartridge that comprises: (a) a sorbent filter material; (b) an end-of-service-life (ESLI) indicator; (c) a housing into which the sorbent filter material and ESLI are disposed, the housing having a sidewall that has a first perimeter; (d) a cover secured to the first perimeter of the housing sidewall, the cover having an air throughput surface and an opaque extension, the opaque extension being positioned on the cover such that the extension is juxtapositioned against an outer surface of the housing sidewall; and (e) a window that enables the ESLI to be viewed through both the housing sidewall and the opaque extension; wherein the window comprises first and second panes, the first pane being present in the opaque extension, and the second pane being present in the housing sidewall.