# bulb/lamp for planetarium



## rmiller (Feb 6, 2004)

Hi everyone,
I am trying to find a bulb that is very bright, has an extremely small filament, and decent life (>100 hrs). I'd like soemthing like the minimag bulb, but it needs to last a lot longer than those. Does anyone have any ideas? The size of the bulb doesn't matter, but the size of the filament size does, since it projects onto the wall and the smaller the better.


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## brickbat (Feb 6, 2004)

Hmm. If you could live with a touch less brightness than the minimag bulb, you could reduce the voltage a tad to prolong the life. Or, how about a Luxeon low-dome - they put out more light than a minimag, are quite small, and have a blue-white color. Or, if you need even more light, there are some 10 and 20 Watt 12V halogen bulbs commonly available in most home centers - they're commonly used on small desk lights and under-cabinet fixtures.


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## Mark_Larson (Feb 9, 2004)

I'm sorry, but do "bright" and "mini-mag bulb" belong in the same sentence? /ubbthreads/images/graemlins/icon3.gif


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## rmiller (Feb 9, 2004)

I can't use the Luxeon because it is directional. I need equal amounts of light in all directions. The halogen bulbs are too big (well the filaments are). The problem is the filament size because it projects onto the wall and you can see it, which makes for pretty poor non-circular stars.


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## James S (Feb 9, 2004)

Sounds like you need a fiber optic running into a tiny round diffuser of some kind. You can use any light you like to light up the other end of the fiber. That way you can get a good bright pinpoint source and not have the bulb located in the projector at all.

real fiber optic illuminators are expensive, nothing under $100 or so and many MUCH more expensive. But if you're really looking at the brightness of a mini-mag bulb, then you can build your own with a regular light bulb or luxeon or whatever and it will work fine. Since the brightness is so low, you might be able to use a little glass bead either sanded or sprayed with something to make it diffuse as the diffuser. There will be a dead spot in the direction that the fiber, but the same would be true for a regular light bulb as it would need to have a base and a wire.


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## brickbat (Feb 11, 2004)

Do you really need 'equal light in all directions"? or might a hemispherical pattern do? The low domes cover nearly a hemishpere.

Give us some numbers - what's the max size of light source that's tolerable? How many lumens do you need?

How about an automotive D2S HID lamp - their arc length is about 5mm. Or do you need something smaller?

I'd suggest posting on sci.engr.lighting - there seem to be some folks there with a pretty good background in lamps.

Tell us more about your project. What size sphere are you using? What size is the room?


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## rmiller (Feb 12, 2004)

Yes a hemispherical pattern would work? It should be as small as possible because you can see the reflection of the glass if it is too big. The sphere is about 6" in diameter and the ceiling height should be about 8' and the length and width of the room will be a little more than 9'. It should be able to work in a variety of rooms though. The D2S would not work since the shape of the bulb and filament wouldn't create round stars on the ceiling and walls. I need a bulb that is fairly round with no sharp curves. The filament size must be small (about 1-3mm) and it must be able to run off a 12V source or less. I would like it do have an MSCP >= 1. I appreciate all the help. Thanks


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