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High Intensity Discharge lamps 101

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gailgrove:
Jace any where I have looked they say LPS is a HID, including the manufactures  :-\

Medved:
@gailgove: Marketing-wise it is, indeed, closer to HID's (due to their application - lot of lumens, but cheap in energy use, color quality not a factor).

But technically it is low pressure discharge lamp, exactly the same as fluorescents (large, long surface of low brightness, discharge occupy the whole cross-section of the arctube, touching it's walls, low current density in the discharge,...).
So from technical perspective, the LPS is not considered as HID.

Vince:
*** CONCLUSION ***

I hope this article have answered to a couple of your questions about HID lamps. This article is mainly intended for beginners who just got into hobby lighting. There is of course a whole bunch more theory about lighting, and I could make other articles about other lighting sources in the future if members show interest to it.

But to conclude this very article, we could summarize the three major HID sources in this list:

MERCURY VAPOR

PROS:

- Simple gears, easy to use.
- Impressive reliability
- Choice of soft, white, non-glaring light (/DX, /C, etc.) or bright, crispy, high-contrast light (/A).
- Specialty applications (/Y, /BLB etc.)

CONS:

- Lamps are considered toxic waste (Hg), special disposal required.
- Lamps dim out over time, especially with newer, cheaper lamps.
- Relatively inefficient, compared to other HID sources, but still as efficient as fluorescent tubes and more than incandescents.

HIGH PRESSURE SODIUM

PROS

- High efficiency, reaching 140 lm/W with highest wattage lamps.
- Spectrum of the lamps raises contrast and overall visibility (perfect for hazardous roads or other similar applications)
- HPS systems start at lower temperatures.

CONS:

- More or less monochromatic light leads to very low CRI.
- Ignitor adds a part to the ballast, making it more likely to fail
- Cheap HPS lamps can fail much earlier than their cheap MV counterparts. They are prone to sodium leak or premature voltage rise (early cycling), those problems are inexistant with MVs.
- Cycling lamps left for too long can damage some ignitors.
- Lamps are more sensitives to line voltage variations.

METAL HALIDE

PROS:

- Exceptional quality of light.
- Various configurations available (probe start, pulse start, CMH).
- Wide choice of whites (2700K, 3500K, 4100K etc.)
- Development not yet done, improvements are still to come.

CONS:

- Ballasts prone to the same problems as HPS, though probe start ballasts can be as reliable as mercury ballasts.
- Some lamps can explode at EOL. Though rare, type E or S lamps can indeed burst is pressure rises due to various reasons.
- Cheap MH lamps can have poor last mixes, making their color ununiform from a lamp to another.
- Color shift through the lamps' life can appear annoying when a large number of lamps is used in a given area (tint difference from one lamp to another).
- Metal halide equipment is still kind of expensive.

gailgrove:
Hang on Vince, HPS are not monochromatic your thinking of LPS, there is still colour rendering under HPS  ;)

Vince:
Edited ;) I added "More or less" LOL.

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