Early-1990s Philips TUV 16W HF

The special lamp featured here is a quartz replica of a standard TL'D' 16W HF, made by skilled glassblowers at Philips's Central Lighting Laboratory in Eindhoven, the Netherlands, for plasma diagnostic purposes. The fused silica material employed here permits an optical access to mercury's emission in the shortwave ultraviolet, especially the element's resonant lines at 253.7 and 184.9 nm. The TL'D' HF type of fluorescent tube was introduced around the mid-1980s and differs from standard TL'D' lamps in that their buffer consists of a neon-argon Penning mixture instead of the usual Ar-Kr mix. This change was implemented in order to optimize the lamp's operation and efficiency at high-frequency (28 kHz).

The neon-mercury discharge presents some interesting characteristics which were the subject of technical investigations at Philips during the 1990s. One of the characteristics is the propensity of the discharge to change color at low temperature and when the drive current exceeds a certain level. This occurs as a result of neon taking over mercury in the production of light as the discharge becomes depleted of mercury atoms, either because of a too low vapor pressure (low temperature) or as a result of a too strong ionic pumping of mercury to the wall (high current).

Interestingly, the first phenomenon was the subject of investigations at Philips during the 1920s in order to solve the problem of the company's "blauwbuis" ("blue tube" in Dutch, a cold-cathode Ne-Ar discharge lamp) turning red during wintertime. This was eventually solved by replacing the neon fill by argon, which paved the way to the development of the standard fluorescent lamp during the 1930s. What was an issue back then became a point of interest seventy years later and led to a research project in co-operation with the Technical University of Eindhoven in 1996. The main goal of this particular scientific investigation was to better understand the plasma phenomena at play under different operating conditions. The gathered knowledge was then used to support the development of color-tunable lighting systems based on the neon-mercury discharge.