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Dimming a 1.2 kW short-arc metal halide lamp Jacketed single-ended metal halide short-arc lamps are remarkable in the fact that they can be dimmed down to 40 % of their nominal wattage without resulting in a significant shift in light color or in any major loss of color quality. This is the result of an optimized thermal management that leads to a very limited burner cold-spot temperature variation over a wide input power range. The picture above shows an Osram HMI 1200W Event operated at nominal power (1200 W, left) and at its lowest power setting possible (480 W, right). The aspect of the arc changes greatly between the two settings, and its structure, with a mercury-dominated hot core and a metal halide outer mantle, is clearly visible at low power. Keywords: Lamps

Dimming a 1.2 kW short-arc metal halide lamp


Jacketed single-ended metal halide short-arc lamps are remarkable in the fact that they can be dimmed down to 40 % of their nominal wattage without resulting in a significant shift in light color or in any major loss of color quality. This is the result of an optimized thermal management that leads to a very limited burner cold-spot temperature variation over a wide input power range. The picture above shows an Osram HMI 1200W Event operated at nominal power (1200 W, left) and at its lowest power setting possible (480 W, right). The aspect of the arc changes greatly between the two settings, and its structure, with a mercury-dominated hot core and a metal halide outer mantle, is clearly visible at low power.
_IMG8194m.jpg Sylvania_MP500T16.jpg Osram_HMI_1200W_Event.jpg Sylvania_H38-4JA21C_b.jpg _IMG2041.jpg
Lamp/Fixture Information
Manufacturer:Osram
Model Reference:HMI 1200W Event
Lamp
Lamp Type:Metal halide short arc
Filament/Radiator Type:Highly loaded arc in metal halides
File information
Filename:Osram_HMI_1200W_Event.jpg
Album name:Max / Misc lamps and lighting
Keywords:Lamps
Filesize:465 KiB
Date added:Dec 19, 2024
Dimensions:1200 x 670 pixels
Displayed:19 times
Model:Z 6_2
Software:Adobe Photoshop CS5 Windows
URL:https://trad-lighting.net/gallery/displayimage.php?pid=617
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Comment 1 to 4 of 4
Page: 1

Ria   [Dec 19, 2024 at 05:00 PM]
Interesting, how is the dimming done, is it just a reduction in supply voltage or is it something more complicated..? Wonder
Max   [Dec 20, 2024 at 12:07 AM]
It's a bit more elaborate in the present case, the current is lowered while keeping the open circuit voltage high (about 400 V) to ensure that the discharge won't extinguish. The issue with the (fast) dimming of MH arcs is that the re-ignition voltage every half cycle tends to increase a lot during the ramp down phase, which has to do with the radiated output becoming temporarily greater than the power input due to the arc's thermal inertia. For this reason dimming ballasts for MH lamps use several tricks to prevent self-extinction of the lamp, such as a slow ramp down schedule, or a high open circuit voltage, or a fast-switching low-frequency square wave current waveform, or a combination of those...
Tuopeek   [Dec 20, 2024 at 08:55 PM]
Interesting how different the arcs look at the two power settings yet the overall colour temperature remains stable. I'd say this is quite an achievement knowing some halides to change colour by orientation without a change in power. I have a blue halide supposed to be rated at 150W but it become much more blue shifted when running at 70W.
Max   [Dec 31, 2024 at 09:40 AM]
The CCT stability of single-ended jacketed MSR/HMI lamps is quite an achievement indeed. It is also interesting to see that this particular technology originated in the early 1980s with Philips's tin halide SN lamps, which were later adapted for an operation with a different fill chemistry.

In the case of blue indium halide lamps, the trend of the light color becoming less saturated at higher power is a well known characteristic of that technology as a higher arc temperature and/or a higher vapor pressure result in a broader emission spectrum from indium mono-iodide. While this is certainly an issue in colored floodlighting applications, such properties of the indium halide arc was used to great benefits in narrow-gauge film projection (cf GE's MARC and Gemini lamps).

Comment 1 to 4 of 4
Page: 1