Re: Scored a Nice 16" Parabolic Reflector. HID or Short Arc? Test Beamshots w/ HID.
They use a GE MARC-300/35K projection lamp
OK, thanks to both of you for the info about that lamp.
As I recall from earlier discussions, these Xe Hg lamps have much more stringent cooling requirements, with both ends needing cooling, and are extreme pressure lamps, with overpressure even when cold, so the cooling needs to be right. Not sure I can pull off using one in my light. What do you guys think, would Xe Hg work for me?
I am going to keep looking for "any position" options I can mount & cool axially in my reflector, and run with my Oriel PS gear, which is DC.
Osram XBO lamps have similar form factor to the HBO, and they work in any position, so these are one clear option. I initially picked HBO instead of XBO due to HBO having about 4-5x more lumens for same power. Sounded good on paper!
Lesson learned: Super high pressure Hg short arc lamps, the Osram HBO variety at least, require you to know, and comply with, the orientation specification. I wish I hadn't seen conflicting specification, indicating S90 orientation in the one source. I allowed that to persuade me it would work. Now, I know it was bad info.
On the positive side, I should already have achieved a good beacon mode, aiming straight up, with the HBO lamp currently installed. When I get more time, I will get some comparison beamshots for HBO vs the 35W HID I initially used. That will be a big moment for my project. I expect the HBO will absolutely destroy the HID in both beam visibility and collimation. It should have about 30x the arc intensity of the HID.
Beacon mode (straight up, not a strobe like with LED beacon mode) was one of my main goals, so this would be a partial success. But, the drawback with HBO of not being able to maintain good brightness when aiming at targets on earth is a big disadvantage. So, maybe that is a new piece of info for the CPF community, from my adventure.
I will also try higher amperage on the HBO in horizontal orientation, to see if it will re-stabilize at rated power with more current. But I don't want to do that in the reflector, in case I pop the lamp. It is clearly risky running a lamp outside recommended parameters like that. I will need to devise a test enclosure. Also, from BVH's recent experience destroying a power transistor when a lamp failed in one of his IR illuminators, I suppose I might hurt the PS if an electrode vaporizes and coats the envelope with a dead short of metal. Since the Oriel is current regulated across a broad range of loads, maybe that less of a risk.
Perhaps I should have taken the MHI route instead (used the MSR400SA lamps I originally bought). Those are any-position lamps, but they are AC lamps. Lightsward had suggested some workable HMI lamps and ballasts by Jenbo. These lamps are interchangeable with the MSR lamps I initially planned to use, and I still have one left. New Jenbo ballasts are priced similar to what I spent on the used Oriel gear. Arc length is about 3x as long as the HBO lamp at similar power, but output is 3x higher. I think that would have been a workable solution. But I can't give up on the DC power supply and ignitor, yet. MHI Lumens are impressive, but they do not develop nearly the same arc intensity as a DC short arc lamp. And spending again for a different PS would hurt!
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Interim Summary (or TL;DR): I now think MHI lamps would have been easier, lighter/more compact electronics, brighter, and similar cost vs the DC SA lamps. But much lower intensity.