The Tiffen 4 x 5.65 IRND Filter Kit includes four filters with densities of 0.3, 0.6, 0.9 and 1.2, allowing you to reduce the transmission of visible light, as well as far-red and infrared light pollution by 1, 2, 3 and 4 stops respectively.
These filters are a combination of both infrared control filters and neutral density filters.
An IRND is ideal for HD cameras, which have greater low-light sensitivity and, subsequently, an increased susceptibility to IR contamination. When using standard neutral density filters to counter the increased light sensitivity afforded by the HD sensor, the effects of infrared pollution become more apparent. These filters combine an ND filter with a comparable IR control filter to eliminate the spill of infrared light reaching the sensor while still maintaining the extra exposure benefits of a neutral density filter.