Metal additive lamp ballasts differ from standard mercury
vapor lamp ballasts. Most important, their volt/amp characteristics
are “softer.” The metals inside the doped lamps
create electrical noise in the secondary circuit of the ballast.
This interference would cause the lamp to go out (normally
during lamp warm-up) when operated by an ordinary ballast.
The additive ballast “absorbs” these pulses in
a way similar to a pneumatic tire absorbing bumps in a rough
road. This also protects the other components in the system,
with the added benefits of longer capacitor and lamp life,
even for standard mercury lamps.
Another difference in the additive ballast is the output
voltage wave shape while the lamp is in operation. The peak
voltage is increased by approximately 30% to handle re-striking
(120 times per second at 60 Hz, AC). “Off-time”
is also minimized to keep the re-striking voltages at a minimum.
The net result is slightly greater lamp output.
There are some trade-offs with the additive ballast. It is
slightly larger and costs more than a standard mercury ballast.
It takes more power to energize the transformer, so increased
efficiency from a greater lamp “on-time” is offset
by the ballast’s higher power consumption.
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