[spleify]

Originally posted by PaulErik
The lamp in the test picture looks to be a mercury vapor lamp because the arc length is too long for it to be a 175-watt metal halide lamp. GE does not manufacture a 6500K MH lamp.

The ballast inside the Regent and other brand 175-watt MV security lights are a normal power factor high reactance autotransformer (HX-NPF) ANSI H39 mercury vapor ballast. These are not even close electrically to an ANSI M57 metal halide ballast. The HX-NPF ballast is commonly used in these mercury vapor lights because of size and cost of materials to manufacture them.

Mercury vapor ballasts (constant wattage autotransformer CWA and high reactance HX) are considered electrically not compatible with metal halide lamps. The open circuit voltage (OCV) for a 175-watt mercury vapor ANSI H39 HX ballast is too low to reliably start/ignite ANSI M57 spec 175-watt metal halide lamps.

Generally almost all ANSI M57 ballasts are CWA type and always have a high power factor because of the capacitor. The capacitor in this type of system is used only for lamp regulation and power factor correction. The ballast coil voltage is peaked for lamp starting. CWA mercury vapor ballasts use the capacitor for peaking the OCV to start the lamp. Metal halide lamps are not compatible with peaking capacitor systems but this does not apply to this thread.

Usually if you use a metal halide (ANSI M57 spec) lamp on any mercury ballast circuit the lamp will have difficulty starting and staying lit during the warm up phase. The arc usually becomes unstable and the ballast can not support the electrical discharge. This may not be a problem at first but will become apparent once the lamp ages. The mercury ballast has a higher secondary short circuit current and lower OCV than metal halide lamps are designed for. Another difference is the current crest factor (CCF). Mercury vapor lamps can a handle a higher CCF than metal halide lamps. If a lamp is operated with a higher CCF than the maximum rating the lamp will wear out quickly (excessive electrode wear).

Mercury Vapor ANSI H39 Ballast Specification
Open Circuit Voltage: 225-255OCV
Secondary Short Circuit Current: 2.0-3.6A
Current Crest Factor: 2.0CCF Max

Metal Halide ANSI M57 Ballast Specification
Open Circuit Voltage: 285-320OCV
Secondary Short Circuit Current: 1.5-1.9A
Current Crest Factor: 1.8CCF Max

The specifications listed above are general ballast ANSI (American National Standards Institute) standards manufacturers follow.

However mercury vapor lamps are compatible with probe start metal halide ballasts of the same wattage. This is why most probe start metal halide ballasts are rated and labeled for metal halide and mercury vapor (example: ANSI M57/H39).

So does this mean that what he built will work, or won't work? Is it worth building to use?
Thanks
Spleify