In satellite-borne particle characterization instruments, for example, in the solar wind charge-energy-mass spectrometers and ion traps, there is a need to suppress the effect of the 121.6 nm Lyman-alpha line of the hydrogen spectrum, the most intensive line of the solar UV radiation resulting in high level of the detector’s noise. To reduce this effect, the electrodes of instruments are usually covered with electroconductive light-absorptive coatings having low reflectivity at the wavelength of 121.6 nm. In this paper the physical mechanisms are considered applicable to reduce the reflectivity of the A1-based coatings to be applied on electrodes of the particle analyzing instruments. Particular emphasis has been given to the role of three phenomena: (i) multiple light scattering light traps of the rough surface, (ii) diffraction of the incident light at the rough surface of the coating, and (iii) electron scattering in a skin layer. It is presented the behavior of reflectivity of the A1-based coating in the course of mechanical and environmental tests simulating standard shipping, storage, launching, flight, and operating conditions of the space equipment. The noise measurements of the Faraday cups used on board the INTERBALL-1 mission are also given. As the hydrogen is the most prevalent substance in the Universe, perhaps, the 121.6 nm stray light problem is the common one not only for the solar wind missions and solar astrophysics telescopes, but also for the Far UV astronomy and future UV space astrophysics missions.