How good is the reflector in PAR64 lamps?

[jebir]

Hi, my first thread here...

For an upcoming event in my community, where the public is encouraged to decorate their gardens with various light effects, I have got the idea to make a spotlight pointing straight up from my backyard. It shall be presenting a beam of light that is clearly visible for by-passers at a distance (say up to 500-1000 meters). Also, it should be safe to have it illuminated for 3-4 hours unattended.

Because of a limited budget, I first thought of just putting out a 1 kW PAR64 VNSP halogen spotlight but it has a beam divergence of 12° and 9° in X and Y, respectively, and I'm not sure if that it will be percieved as a "beam of light" fom a distance, also, the warmer output from the halogen is not as eye-catching as the blue light of an arc-based lamp.

So, since the reflector is a major cost in such a project, I wonder if it could be worthwhile scavenging the parabolic reflector from a VNSP PAR64 lamp and combining it with a short arc lamp? I'm kind of hoping that the reflector is well made and that the 12° and 9° divergences are due to the filament size.

Anyone have any thoughts about this approach?
Also - any tips on how to make the spotlight stable and safe for extended outdoor operation are appreciated.

Cheers, Jens.

[Benson]

So, since the reflector is a major cost in such a project, I wonder if it could be worthwhile scavenging the parabolic reflector from a VNSP PAR64 lamp and combining it with a short arc lamp? I'm kind of hoping that the reflector is well made and that the 12° and 9° divergences are due to the filament size.

The reflectors are quite good, and ISTR somebody around here doing pretty much exactly that (maybe it was an automotive HID rather than short-arc), though I think on a different size PAR lamp; I distinctly remember pictures of a nice sealed beam with a hole neatly bored through it.*

But I'm not sure how it's gonna do at capturing a short-arc's emitted light -- they emit in a kind of asymmetric butterfly pattern, not more-or-less spherical like an incandescent filament, so you have to make sure the reflector covers the angles where most of the light is. Perhaps one of the local short-arc gurus can tell you whether a PAR64 is a good choice or not, all I can say is that it <i>may</i> be an issue.


*On second thought, maybe it was a recoil LED mod? Same concept, though -- PAR reflectors are good stuff.

[ma_sha1]

I had done PAR46 to HID here:
http://www.candlepowerforums.com/vb/...=1#post3553506

it's OK, got 275K lux, the same 35W HID in 6" alu. reflector does 400klux, so I think the thick lens in PAR lamp blocks quite a bit of light.

[jebir]

Thanks for the encouraging responses.

I was thinking of getting an Osram AluPAR 64 which is a solid aluminum reflector with a glass cover. I can then do away with the glass if it isn't clear ...

It should not be difficult to open the back of the reflector and put a HID bulb in there but I would prefer something more luminous to make the beam more eye-catching for by-passers.

I didn't know that a short-arc lamp has a non-isotropic light emission. Why is that? I suggested it out of ignorance - thinking that a smaller source would be better for a good parabolic reflector to convert it into a beam.

Any other suggestion for an appropriate lamp would be welcome!

Cheers, Jens.

[Benson]

I didn't know that a short-arc lamp has a non-isotropic light emission. Why is that?

Because the electrodes are big in comparison to the arc, and block a significant amount of light in some directions.

I suggested it out of ignorance - thinking that a smaller source would be better for a good parabolic reflector to convert it into a beam.

Which is correct, in general -- you just have to make sure the reflector's a good match, or you could wind up throwing away a lot of your light. Whether you get that correct, or just reasonably close, it'll throw significantly farther than the same lumens from a bigger light source (such as automotive HID), because of the higher source brightness. You'd have to get really bad choice of reflector (like a shallow, long-focus reflector that's basically behind one electrode) to really cripple the light, but the more you're aware of it, the more efficiency (= more lumens in the primary beam) you'll get...

[jebir]

OK... thanks to the insightful responses on my initial idea, I gave up exploring the PAR64 reflector.

Instead I have gotten a deep parabolic spotlight based on a 70 W HID (I think) that I'd like to transform into a blue-beam eye-catcher. The entire unit is a professional architectural spot made from solid cast Aluminum with rubber gaskets and water seals everywhere so it should be good for my intention to use it outdoor unattended for hours.

Now - what smaller and more powerful ligtht source do you guys suggest replacing the 70W HID with so that I can get a blue beam pointing into the sky?

I wanted to share some photos of the unit but I can't figure out how to make CPF accept my photos. So I just resort to give you the links - sorry about that. (If someone can tell me how to do, I'll edit the post to make them inline.)

The full unit along with a 30 cm (12") ruler:
http://jensbirch.smugmug.com/Photogr...PA101264-L.jpg

And here is a photo from the front showing the 15 cm (6") diameter reflector:
http://jensbirch.smugmug.com/Photogr...PA101261-L.jpg

Here is the beam appearance after centering the bulb (1 sec., f/5.6, ISO 400):
http://jensbirch.smugmug.com/Photogr...PA101267-L.jpg

Here is the electronics box:
http://jensbirch.smugmug.com/Photogr...PA101260-L.jpg

and here is the lamp:
http://jensbirch.smugmug.com/Photogr...PA101266-L.jpg

Close-up of lamp text which appears to be "OSRAM POWERBALL HCI-7C 70W/WDL GERMANY q9b8":
http://jensbirch.smugmug.com/Photogr...1266crop-L.jpg

The following link brings you to my online gallery where you can see all photos full-sized:
http://jensbirch.smugmug.com/Photogr...6361&k=TJzMfjV