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Gas & Gaps - HID/HPS Sodium Vapor
A high-pressure sodium (HPS) light bulb might make an efficient, fast,
maintainance-free spark gap, due to its low forward voltage drop and
off-the-shelf availability.
High pressure sodium, A.K.A High Intensity Discharge (HID) bulbs are the now
most common form of outdoor lighting, giving a more pinkish glow than the
also ubiquitous mercury vapor, which has a bluish tinge.
The pink hue is actualy the alumina (aluminum oxide, or saffire) tube in the
borosilicate glass vaccuum thermal insulation bulb. Which is how you
identify the HID bulb; mercury vapor is frosted like flourescent tubes.
The HID Tube for a typical 40 Watt bulb is around an inch long, 1/8" dia.
with electrodes at each end. It is filled with (Argon?) for starting
purposes. It starts similar to a HeNe laser; around 1500 V narrow pulses
break down the argon, allowing a 120 VAC current to flow, which vaporizes
the condensed sodium. The starting voltage drop is around 10 Volts, but
increases to 60 volts over a few minutes time. The alumina tube, which is
the only transparent thing I know which will withstand those temperatures
and pressures, save diamond, is thermaly insulated by mounting it in an
evacuated borosilicate glass bulb.
If power is interrupted once the lamp is hot, it will not restart until it
cools off, which takes several minutes. The high pressure sodium vapor (10
atm?) increases the breakdown value of the gas.
Potential advanteges:
Ubiquitous, cheap ($20), plug & play component
Sealed, no adjustment or maintenance
Low voltage drop (10-50 V) for high-efficiency
Possibility of triggered operation, via xenon stobe illumination
Potential disadvantage:
What's the hot breakdown voltage? Will it display stable negative resistance?
What is the quench-time?
(I'll bet poor, removing from borosilicate insulating bulb may help)
Needs startup mechanism - can be damaged by overvoltage during startup
Whatever else I'm not aware of :-0
Who's tried this? Who wants to? Who is going to? Bad idea? Amyone interested
in home-made thyratrons or pseudo-spark gaps?