{"id":1636,"date":"2026-05-02T07:30:48","date_gmt":"2026-05-02T07:30:48","guid":{"rendered":"https:\/\/opticalglassfilter.com\/?p=1636"},"modified":"2026-05-02T07:30:48","modified_gmt":"2026-05-02T07:30:48","slug":"what-is-a-long-pass-filter-where-is-it-used","status":"publish","type":"post","link":"https:\/\/opticalglassfilter.com\/?p=1636","title":{"rendered":"What Is a Long Pass Filter & Where Is It Used?"},"content":{"rendered":"
A long pass filter (LPF)<\/strong>, also known as a long-wave pass filter<\/strong> or high-pass optical filter<\/strong>, is an optical component that transmits light with longer wavelengths<\/strong> while blocking shorter wavelengths<\/strong>.<\/div>\n
<\/div>\n
In simple terms:<\/div>\n
<\/div>\n
    \n
  • Shorter wavelengths (UV, blue, violet)<\/strong> \u2192 reflected or absorbed<\/li>\n
  • Longer wavelengths (green, yellow, red, NIR)<\/strong> \u2192 transmitted efficiently<\/li>\n<\/ul>\n
    <\/div>\n
    Long pass filters are widely manufactured as hard coated interference filters<\/strong> for high performance, durability, and sharp cut-on edges.<\/div>\n
    <\/div>\n
    \n
    <\/div>\n

    How Does a Long Pass Filter Work?<\/h2>\n
    <\/div>\n
    \n

    Most industrial-grade long pass filters use multi-layer thin-film coating technology<\/strong> (interference filters).<\/p>\n

    <\/div>\n

    The coating structure is designed to:<\/p>\n<\/div>\n

    <\/div>\n
      \n
    • Allow light above a certain wavelength to pass through<\/li>\n
    • Reflect or block light below that threshold<\/li>\n
    • Provide high transmission in the passband<\/li>\n
    • Offer strong blocking in the stopband<\/li>\n<\/ul>\n
      <\/div>\n
      Common specifications include:<\/div>\n
      <\/div>\n
        \n
      • Cut-on wavelength (e.g., 550 nm, 650 nm, 780 nm, 850 nm)<\/li>\n
      • Transmission rate: >85%\u201395% in the passband<\/li>\n
      • Optical density (OD): OD3 to OD6 for blocking<\/li>\n
      • Hard dielectric coating for high stability<\/li>\n<\/ul>\n
        <\/div>\n
        \n
        <\/div>\n

        Key Features of Long Pass Filters<\/h2>\n
        <\/div>\n
          \n
        • Sharp cut-on edge<\/li>\n
        • High transmittance in the passband<\/li>\n
        • High blocking of unwanted short wavelengths<\/li>\n
        • High laser-induced damage threshold (LIDT)<\/li>\n
        • Stable performance under different temperatures<\/li>\n
        • Custom sizes and wavelengths available<\/li>\n<\/ul>\n
          <\/div>\n
          \n
          <\/div>\n

          Where Are Long Pass Filters Used?<\/h2>\n
          <\/div>\n

          1. Fluorescence Microscopy & Medical Devices<\/h3>\n
          <\/div>\n
          \n

          Long pass filters separate excitation light from emitted fluorescence signals.<\/p>\n

          <\/div>\n

          They are widely used in:<\/p>\n<\/div>\n

          <\/div>\n
            \n
          • PCR instruments<\/li>\n
          • Fluorescence microscopes<\/li>\n
          • Medical diagnostic equipment<\/li>\n
          • Bioimaging systems<\/li>\n<\/ul>\n
            <\/div>\n

            2. Laser Systems & Laser Protection<\/h3>\n
            <\/div>\n
            \n

            Used to block pump light or stray short wavelengths while letting laser beams pass.<\/p>\n

            <\/div>\n

            Common in:<\/p>\n<\/div>\n

            <\/div>\n
              \n
            • Laser pointers<\/li>\n
            • Industrial laser equipment<\/li>\n
            • Laser measurement tools<\/li>\n
            • Laser safety systems<\/li>\n<\/ul>\n
              <\/div>\n

              3. Machine Vision & Industrial Imaging<\/h3>\n
              <\/div>\n
              \n

              Improve image contrast by filtering out blue noise, UV interference, and ambient light.<\/p>\n

              <\/div>\n

              Applied in:<\/p>\n<\/div>\n

              <\/div>\n
                \n
              • Industrial cameras<\/li>\n
              • Inspection systems<\/li>\n
              • Barcode scanners<\/li>\n
              • LED lighting systems<\/li>\n<\/ul>\n
                <\/div>\n

                4. Environmental & Optical Sensing<\/h3>\n
                <\/div>\n
                Used in spectrometers, optical analyzers, and environmental monitoring devices.<\/div>\n
                <\/div>\n

                5. Security & Surveillance Cameras<\/h3>\n
                <\/div>\n
                Especially 850nm and 940nm long pass filters<\/strong> for IR night vision.<\/div>\n
                <\/div>\n

                6. Automotive & Consumer Electronics<\/h3>\n
                <\/div>\n
                Used in:<\/div>\n
                <\/div>\n
                  \n
                • LiDAR systems<\/li>\n
                • Optical sensors<\/li>\n
                • Camera modules<\/li>\n
                • Display panels<\/li>\n<\/ul>\n
                  <\/div>\n
                  \n
                  <\/div>\n

                  How to Choose a Long Pass Filter<\/h2>\n
                  <\/div>\n
                  When selecting a long pass filter, consider these key factors:<\/div>\n
                  <\/div>\n
                    \n
                  1. Cut-on wavelength<\/strong> required by your system<\/li>\n
                  2. Transmission rate<\/strong> in the passband<\/li>\n
                  3. Blocking depth (OD value)<\/strong><\/li>\n
                  4. Operating angle and environment<\/strong><\/li>\n
                  5. Dimensions, thickness, and shape<\/strong><\/li>\n
                  6. Coating type (hard or soft)<\/strong><\/li>\n<\/ol>\n
                    <\/div>\n
                    Most industrial applications prefer hard coated interference long pass filters<\/strong> for long service life and high stability.<\/div>\n
                    <\/div>\n
                    \n
                    <\/div>\n

                    Custom Long Pass Filters Available<\/h2>\n
                    <\/div>\n
                    We provide custom long pass filters<\/strong> with:<\/div>\n
                    <\/div>\n
                      \n
                    • Custom cut-on wavelengths<\/li>\n
                    • Custom sizes and shapes<\/li>\n
                    • Various glass substrates (BK7, quartz, borosilicate)<\/li>\n
                    • High-transmission hard coatings<\/li>\n
                    • Small orders and sample orders welcome<\/li>\n<\/ul>\n
                      <\/div>\n
                      \n

                      If you need help selecting the right long pass filter for your project,<\/p>\n

                      <\/div>\n

                      please feel free to contact us for professional support.<\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

                      A long pass filter (LPF), also known as a long-wave pass filter or high-pass optical filter, is an optical component that transmits light with longer wavelengths while blocking shorter wavelengths. In simple terms: Shorter wavelengths (UV, blue, violet) \u2192 reflected or absorbed Longer wavelengths (green, yellow, red, NIR) \u2192 transmitted efficiently Long pass filters are […]<\/p>\n","protected":false},"author":1,"featured_media":1637,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[36],"tags":[34,32,33,35],"yoast_head":"\nWhat Is a Long Pass Filter & Where Is It Used? | Optical Glass Filter<\/title>\n<meta name=\"description\" content=\"Learn what a long pass filter is, how it works, and its main applications in medical, laser, imaging and industrial systems. 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