Longpass Filters, also known as Longpass Edge Filters, are designed to transmit wavelengths greater than the cut-on wavelength of the filter. Longpass Filters are commonly used to isolate portions of the spectrum in a variety of industrial or life sciences applications including microscopy or fluorescence instrumentation. Longpass Filters are typically designed for a 0° Angle of Incidence, whereas Longpass Dichroic Filters are designed for use at a 45° Angle of Incidence. Longpass Filters can be used with Shortpass Filters to create custom Bandpass Filters. Certain Longpass Edge Filters can also be used as cold mirrors to minimize the heat buildup often caused by infrared radiation. The phrase "High-Pass Filter" is commonly used to refer to frequency instead of wavelength, so "High-Pass Filter" counterintuitively refers to Shortpass Filters, not Longpass Filters. "Lowpass Filter" similarly describes frequency and refers to Longpass Filters.

Edmund Optics offers a wide variety of Longpass Edge Filters for performance in the ultraviolet, visible, or infrared wavelengths. Longpass Filters are available in a range of optical densities. Higher optical densities offer increased blocking capability. TECHSPEC High Performance OD 4 Longpass Filters offer high blocking with superior transmission. TECHSPEC Dichroic Longpass Filters feature hard coatings for increased durability, while offering high performance for use in fluorescence applications or as spectral beamsplitters. Longpass Edge Filter kits containing some of Edmund Optics’ most popular Longpass Edge Filters are also available.