Gas Discharge Lamps, Ballasts, and Fixtures...
Principles of Operation... Trouble-shooting... Repair..
Metal halide lamps...
are constructed along similar lines to mercury vapor lamps.
However, in addition to the mercury and argon, various metal halides are included in the gas fill.
The most popular combination is sodium iodide and scandium iodide.
A few versions of this lamp have lithium iodide as well.
A much less common version has sodium iodide, thallium iodide, and indium iodide.
The use of these compounds increases the luminous efficiency and results in a more pleasing color balance than the raw arc of the mercury vapor lamp.
Thus, no phosphor is needed to produce a color approaching that of a cool white fluorescent lamp with more green and yellow than a mercury vapor lamp (without correction).
Some metal halide lamps have a phosphor that adds some orange-ish red light, but not much, since the metal halide arc does not emit much UV.
Mercury vapor lights...
are a poor choice for growing.
There are two basic problems with mercury vapor lamps.
First, they are not as efficient at turning power to light as HPS or MH lamps are.
Using the same current, they emit less than half the light as an HPS and only 60% of an MH.
Secondly, mercury vapor lamps, even with improved spectrums, emit a lower percentage of useable light than the more efficient lamps.
High pressure sodium vapor lamps...
contain an internal arc tube made of a translucent ceramic material (a form of aluminum oxide known as "polycrystalline alumina").
Glass and quartz cannot be used since they cannot maintain structural strength at the high temperatures (up to 1300 degrees C) encountered here, and hot sodium chemically attacks quartz and glass.
Like other HID lamps, the arc tube is enclosed in an outer glass envelope.
A small amount of metallic (solid) sodium in addition to mercury is sealed in a xenon gas fill inside the ceramic arc tube.
Some versions of this lamp use a neon-argon mixture instead of xenon.
Basic operation is otherwise similar to mercury or metal halide lamps.
High pressure sodium vapor lamps produce an orange-white light and have a luminous efficiency much higher than mercury or metal halide lamps.
Metal halide lamps are much more efficient, generally around 50 to 75 percent more efficient than fluorescent lamps.
High pressure sodium lamps are roughly twice as efficient as fluorescent lamps.
When cold, the metallic mercury or sodium in the arc tube is in its normal state (liquid or solid) at room temperature.
During the starting process, a low pressure discharge is established in the gases.
This produces very little light but heats the metal contained inside the arc tube and gradually vaporizes it.
As this happens, the pressure increases and light starts being produced by the discharge through the high pressure metal vapor. A quite noticeable transition period occurs when the light output increases dramatically over a period of a minute or more.
The entire warm up process may require up to 10 minutes, but typically takes 3 to 5 minutes.
A hot lamp cannot be restarted until it has cooled since the voltage needed to re-strike the arc is too high for the normal AC line/ballast combination to provide.
H.I.D. Conversion Lamps –
There are two types of conversion lamps:
A. Sodium Lamps which run on halide ballasts - are the most common.
B. & Halide Lamps which run on sodium ballasts.
IMB
Principles of Operation... Trouble-shooting... Repair..
Metal halide lamps...
are constructed along similar lines to mercury vapor lamps.
However, in addition to the mercury and argon, various metal halides are included in the gas fill.
The most popular combination is sodium iodide and scandium iodide.
A few versions of this lamp have lithium iodide as well.
A much less common version has sodium iodide, thallium iodide, and indium iodide.
The use of these compounds increases the luminous efficiency and results in a more pleasing color balance than the raw arc of the mercury vapor lamp.
Thus, no phosphor is needed to produce a color approaching that of a cool white fluorescent lamp with more green and yellow than a mercury vapor lamp (without correction).
Some metal halide lamps have a phosphor that adds some orange-ish red light, but not much, since the metal halide arc does not emit much UV.
Mercury vapor lights...
are a poor choice for growing.
There are two basic problems with mercury vapor lamps.
First, they are not as efficient at turning power to light as HPS or MH lamps are.
Using the same current, they emit less than half the light as an HPS and only 60% of an MH.
Secondly, mercury vapor lamps, even with improved spectrums, emit a lower percentage of useable light than the more efficient lamps.
High pressure sodium vapor lamps...
contain an internal arc tube made of a translucent ceramic material (a form of aluminum oxide known as "polycrystalline alumina").
Glass and quartz cannot be used since they cannot maintain structural strength at the high temperatures (up to 1300 degrees C) encountered here, and hot sodium chemically attacks quartz and glass.
Like other HID lamps, the arc tube is enclosed in an outer glass envelope.
A small amount of metallic (solid) sodium in addition to mercury is sealed in a xenon gas fill inside the ceramic arc tube.
Some versions of this lamp use a neon-argon mixture instead of xenon.
Basic operation is otherwise similar to mercury or metal halide lamps.
High pressure sodium vapor lamps produce an orange-white light and have a luminous efficiency much higher than mercury or metal halide lamps.
Metal halide lamps are much more efficient, generally around 50 to 75 percent more efficient than fluorescent lamps.
High pressure sodium lamps are roughly twice as efficient as fluorescent lamps.
When cold, the metallic mercury or sodium in the arc tube is in its normal state (liquid or solid) at room temperature.
During the starting process, a low pressure discharge is established in the gases.
This produces very little light but heats the metal contained inside the arc tube and gradually vaporizes it.
As this happens, the pressure increases and light starts being produced by the discharge through the high pressure metal vapor. A quite noticeable transition period occurs when the light output increases dramatically over a period of a minute or more.
The entire warm up process may require up to 10 minutes, but typically takes 3 to 5 minutes.
A hot lamp cannot be restarted until it has cooled since the voltage needed to re-strike the arc is too high for the normal AC line/ballast combination to provide.
H.I.D. Conversion Lamps –
There are two types of conversion lamps:
A. Sodium Lamps which run on halide ballasts - are the most common.
B. & Halide Lamps which run on sodium ballasts.
IMB
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