8540.20.20 - Cathode-ray tubes

This category encompasses cathode-ray tubes (CRTs), which are vacuum tubes that emit a focused beam of electrons to create a visible image on a phosphorescent screen. CRTs are a foundational technology for older display devices, including televisions and computer monitors. While their use has declined with the advent of newer display technologies, they remain relevant for certain legacy applications and specialized equipment.

Within the broader group of thermionic, cold cathode, or photocathode tubes, cathode-ray tubes are specifically distinguished by their electron beam generation and deflection mechanisms used for image formation. This distinguishes them from other types of tubes classified under 8540, such as mercury arc rectifying tubes or television camera tubes.

This classification further subdivides based on the type of image produced. The subcategories of "Color" and "Other" reflect this distinction. "Color" CRTs are designed to display images with a full spectrum of colors, typically achieved through the use of multiple electron guns and a shadow mask or aperture grille. The "Other" subcategory would encompass monochrome CRTs, which display images in shades of a single color.