When a part is genuinely interchangeable across lamp types, classification typically follows the general rules for parts not identifiable as suitable for use solely or principally with a particular article. In practice, technical documentation showing the part's design intent and primary application is the most reliable basis for classification — and a CBP binding ruling is advisable for high-volume or high-value components where the answer is not clear-cut.

Not necessarily. Phosphor materials in bulk form are typically classified as chemical products rather than lamp parts, even when their primary commercial use is lamp manufacturing. Only when a phosphor is presented in a form specifically prepared and dedicated for lamp assembly — such as a pre-coated glass tube — might a lamp-parts classification be arguable. Chemical classification of the base material generally prevails for bulk phosphor imports.