2002 Philips CLEO 15W

The CLEO 15W is a special fluorescent tube emitting primarily in the UV-A domain for suntanning applications. The present model is the latest and smallest variant released in the early 2000s for compact and portable facial suntanner systems. The lamp has the physical size of a standard 8 W T5 fluorescent tube (288 mm length, 16 mm diameter) and yet is driven at nearly twice that power level so as to increase its surface irradiance. Interestingly, a standard argon buffer is used instead of the usual neon- and helium-based buffer gas mixtures employed in larger high-output lamps. The reason for this lies in the fact that the light noble gases needed for the optimal operation of the mercury discharge at high current increase also the electrode losses. In large lamps, the increased performances of the mercury discharge are enough to overcompensate for the reduced electrode efficiency, resulting in net positive performances. However, this is not the case in smaller lamps such as the CLEO 15W because of the much greater electrode loss fraction.

The lamp is internally coated with a layer of BSP phosphor (lead-activated barium disilicate) of the kind used in black light fluorescent tubes. This material converts shortwave radiation from the mercury discharge (primarily 185 and 254 nm resonance lines) into a broadband light emission between 300 and 400 nm with a peak at 352 nm. The glass bulb then filters out the shorter-wave end of the fluorescence spectrum, resulting in a limit at 313 nm. The spectral emission of the 15 W Cleo is similar to that of Philips's standard color-09 suntanning tubes, which use the same phosphor. These lamp types differ in their UV-B to UV-A ratio, which is the lowest in the CLEO (0.7 % vs. 1.0 %) so as to reduce the risk of erythema. This change is obtained by a slightly different glass formulation which results in an increased UV-B absorption. Because of its energetic emission spectrum, CLEO lamps could also be used in certain technical applications such as photochemistry and material ageing. At Philips, this lamp was used for the calibration of Ulbricht (integrating) sphere and other light-measuring equipment. The 15 W CLEO has a very stable and reproducible output when driven on a stabilized current source in a temperature-controlled environment. Incidentally, the lamp temperature can be checked via its operating voltage, and the latter was usually finely adjusted by way of ventilation in a quartz jacket.