This option adds an additional 2 filter positions to the FH-SS filter holder. The FH-SS and FH-SS-ADD option are designed to be used with Sciencetech FT-75-3 type blank filter holders as well as filters that include the -FT option. The FH-SS filter holder is used with Sciencetech's line of Fully Reflective solar simulators as well as the Solar Lightline and SciSun solar simulators.