1980s Philips MNL-G (6.5 W)

The cold-cathode discharge lamp technology was extensively investigated and developed at Philips in the Netherlands from the 1910s till the 1990s. The peculiar model featured here was made at the company's central lighting laboratory in Eindhoven during the 1980s and was designed specifically for a use in marine navigation lights in place of traditional incandescent lamps.

The lamp's structure is unlike that of any other argon-mercury-filled CCFLs. First of all, the MNL-G features a compact discharge tube enclosed inside an evacuated outer jacket whose role is to ensure a high luminous output even in the coldest weather. Next, the discharge tube has a unique design which consists of a massive central glass structure fused to a outer glass tube. This assembly shapes the electrical discharge into a compact helical structure which is instrumental for the realization of a high source brightness. Since this particular lamp is meant to be used in a starboard light, this helical structure is internally coated with a green-emitting cerium-magnesium aluminate (CAT) phosphor, excited by a discharge in mercury vapor. Interestingly, the fluorescent coating was actually applied before the burner components were fused together. Although this raises the risk of damaging the phosphor during the manufacturing process, such design maximizes the source brightness, which is critical to the intended application. Finally, the burner is sealed with a pair of annular metal cup electrodes configured in such a way so as to work as hollow cathodes for the efficient emission of electrons.



Although the principles of marine navigation lights using cold-cathode discharge tubes originates from work done at the US Naval Research Laboratory during the 1960s, Philips certainly pushed the concept to extremes in terms of thermal management and source brightness. However, it is unclear if the MNL-G shown here was an experimental model built only as a proof of concept, or if the Dutch actually developed and made a series of these lamps at a client's request. In any cases it is certain that a neon-filled version was also made for the port-side light, although there was no need for an evacuated outer jacket and an internal phosphor coating (while a YOX phosphor could certainly deliver some valuable red light to saturate the emitted light color).