Hoya Infrared- 55mm filters block all visible light letting only infrared light in different wavelengths pass. The number in the filter name (R72) is an indication of the cut-off point for visible light, in this case, 720 nanometers (720nm), the higher the figure, the more the filter ignores visible light. Infrared filters are constructed of optical precision ground & polished glass & appear black to the human eye. The HOYA Infrared R72 filter will enable you to create amazing black & white images with a hint of cyan & magenta. This type of filter is also used in crime detection, medical photography, detection of distribution of vegetation, etc.