2000 Sylvania MS400/PS/BU-Only

Sylvania was one of the first company to develop and release pulse-start metal halide lamps in North America. The introduction of a pulse ignitor in American MH lamp control gears enabled the removal of the starting probe from the burner, which could thus be designed in wattages below 175 W. Another benefit of such change is that the argon fill pressure in the arc tube could be increased from 20 mbar to 100 mbar and beyond, which led to a much improved lumen maintenance since the rate of electrode damage during starting is much reduced compared to the situation in standard probe-start MH lamps. The first lamp with such an improved design was the 100 W Metalarc introduced in 1984.

The pulse-start technology was applied exclusively to low-wattage metal halide lamps until the mid-1990s. In 1995 Sylvania released the first pulse-start high-wattage quartz metal halide lamps and the technology was applied to other lamp types during the second half of the decade. This refresh of the QMH (Na-Sc) lamp technology culminated in 2000 with the introduction of this MS400/PS/BU-Only whose performances are the best in the 400 W quartz MH lamp class (including European lamps). Interestingly, while Sylvania published an initial output of 42 klm for this lamp type, more than 44 klm was actually measured, which puts the lamp's efficacy at an impressive 111 lm/W!

The reason behind this improved performance can be found in the measured light color temperature of 3766 K, which is 234 K lower than the listed 4000 K. This difference is clearly due to a higher sodium vapor pressure caused either by a salt mix with a higher Na/Sc ratio than in standard Metalarc lamps, or by a higher salt dosage. It is highly likely that Sylvania actually changed the salt dosage in order to surpass the performances of lamps made by the competition (GE and Venture list 44 klm as the initial output of their own variants of this particular lamp).

In order to achieve high performances, the lamp was designed for an operation exclusively in the vertical position. In this situation the thermal losses in the burner are minimized since the arc remains centered along the lamp's axis. In order to optimize the energy efficiency of the discharge the salt vapor pressure in the burner is kept as high as possible. To this end one extremity of the arc tube is provided with a very deep coat of zirconium oxide whose purpose is to limit heat losses further and keep the cold-spot temperature as high as possible (note how far this coating extends over the burner surface). In the present case this coating is on the side opposite to the lamp cap for an optimum operation in the base up position in high-bay luminaires.

Although Sylvania already used such an asymmetric burner coating in its Super Metalarc /BU of the probe-start kind since the mid-1970s, the implementation of the pulse-start design led to a much improved output maintenance over time. While the probe-start 400 W Super Metalarc /BU outputs 26.0 klm at 40 % life, the present pulse-start version emits 32.8 klm (+26 %) at the same point in time. That's the published data. In the case of the present lamp, it is estimated that given its initial output flux, it will emit close to 35 klm at 40 % life. The performances averaged through life of this lamp are thus far superior than those of the probe-start Metalarcs (Super or standard).

Like all enclosed-rated Metalarc lamps produced by Sylvania, this MS400/PS/BU-Only is built with a split frame whose purpose is to limit the rate of sodium loss from the burner. Equally important is the lack of side frame wire which ensures that the arc remains straight throughout the lamp life since no significant magnetic forces are exerted on the discharge. In order to ensure a reliable discharge ignition the burner is exposed to the UV radiation from a small capacitively-coupled capsule mounted on the frame near the lamp cap. Moreover, the purity of the lamp's nitrogen fill is maintained thanks to a barium peroxide getter mounted also in the same location. This getter critically prevents the build up of hydrogen, a very light gas which effuses mainly from the glass bulb and which can affect ignition negatively if it accumulates inside the burner.

With its class-leading performances the MS400/PS/BU-Only became a good alternative to the standard 400 W high-pressure sodium lamps in high-bay lighting applications. While there is a significant difference in light output between the two lamps (-11 % from 50 klm), the warm neutral-white light color from the MH lamp is far more pleasing to the eye, which is of importance in public areas such as bus and train stations, parking lots, etc... As a result, the market penetration of medium and high-wattage pulse-start metal halide lamps became quite significant in North America and when medium-wattage ceramic MH lamps were released in the early 2000s the quartz version became a sort of low-cost alternative in the high-end HID lamp segment.