Hollow cathode lamps historically fell under Chapter 90 (specifically as parts or accessories of spectrometers under heading 9027) because they are dedicated consumables explicitly designed for atomic absorption (AA) instruments.

The shift away from Chapter 90 occurred due to tightening international customs interpretations and World Customs Organization (WCO) guidance regarding parts versus general electrical lamps.

• The Classification Conflict: Chapter 90, Note 2(a) dictates that parts and accessories which are goods included in any of the headings of Chapter 85 (like electric lamps under heading 8539) are always classified in those headings regardless of their specialized use.
• The Transition: While individual customs authorities issued binding rulings at different times depending on local audit challenges, the global enforcement that standalone specialized lamps (such as hollow cathode and deuterium lamps) must be classified by their physical nature as discharge lamps rather than instrument parts solidified across major jurisdictions during the 2000s and 2010s harmonization updates. This moved them definitively into subheading 8539.39 (or 8539.31 depending on specific cathode configurations). which is subject to 20% import duty in South Africa