You know, it seems the biggest problem with using parabollic or ellipsodial reflectors is the lamp becomes an obstruction to itself. People try to minimize this by mounting the lamp axially inside the reflector, but all metal halides (at least the ones that I've seen) seem to have some sort of cap on the ends of the arc. (usually white) I'm not sure what its made of. It looks like plastic but obviously its not. Anyways, this little cap blocks light from moving straightforward when the bulb is mounted axially and produces a small round shadow in the center. (see lucky me' parabollic reflector tests)

I have three different halide lamps. A Philips from Home Depot, a Ushio and the Venture. All three of which have this little white cap on the ends of the arc.

I tried browsing around on hid direct to look at other bulbs but they don't show many pictures.

So the question is: do any metal halide lamps exist without these little caps on the ends? Or are they necessary for all?

I mean think about it. If we didn't have the lamp getting in the way of itself, what we could do with a small ellipsodial reflector... just thinking about it is... is.... ROMANTIC!

Here it is.
OSRAM HSD 575 The Ballast is $2,000 the lamp is $130

Click to view attachment

It’s not actually the lamp getting in the way it’s the lack of reflector where the lamp goes through that causes the dark spot. With careful design it can be reduced to practically nothing.

DJ

Still, how is light going to get through if theres a cap in the way?

2,000 dollars? Ouch! x_x

There is very liitle light going thru the top or the bottom, mostly straight out the sides, here is a plot from OSRAM for the HMI 575 bulb but most others are similar.

The light goes around the arc. Read thispost Now if the arc is moved forward in an elliptical then it will start to collimate part of the arc like a parabolic so it will fill the dark spot with light. The dark spot is still there but at one position the end of the arc can fill this spot. By careful adjustment this position can be made to occur at the LCD.
I'll try to do a trace.
DJ

From what I could tell, the white endcaps are made of glass. The whole arc is just a tube that is pinched at the ends. The white part, it is paint - I don't know what kind of paint, but its looks to me like a special paint. I have no idea of the purpose. Well, in any event that is my opinion.

The bulb is an Obstruction to itself, and it always will be. Sure we are missing part of a reflector when we have a hole to insert the bulb, but that's only part of the problem. Any glass, even though it is clear, it serves as an obstruction. It reflects light, it refracts light, it causes shadows.

The ideal type of light source we all know would be one with no physical enclosure, no hook up wires and no mounting assembly. Just a light source that was a perfect spot like a mini-star.

I'd be interested to know what the white part of the arc tube's function is if anyone finds out. Be sure to post the info.

The reflector that they use like the Altman and in fact the function of an ellipsoid reflector relies on the light from the side of the lamp for over 90% of the light gain. The top of the lamp output doesn't mater much what maters is how far forward the top of the lamp is or how tall it is. The taller it is the more it will block the light from the reflector

You can get just the arcs. I could provide them but I won't. Without the outer glass envelope the arc is very dangerous. The UV and explosion risk is very real. I've seen recently a group of people using short arc lamps on other forums. They are actually taking pictures of these arcs burning, which tells me they are stupid or uninformed about the risks. These lamps do not provide any kind of UV filtration, it is the arc tube itself that is shown. In a properly designed light rig with proper handling techniques these lamps can be very effective, but as I have seen them used recently they are just dangerous experiments.

Yes standing if front of a un- protected arc lamp is dumb with out protection. Yet those lamps they are using fit many commercial PJ. Should they not sell that type of PJ?? Let's just not spend time sun tanning in front of a un-protected lamp arc.

If you can get just the Arc's, and if you can get a custom lamp made, would it not be beneficial to have one made like the $130 lamp Arizona Video posted? Why do we need such a large enclosure for? The only reason I can think of it exisitng is either a buffer for an explosion, or a buffer for intense heat. Other than that is there any reason why these lamps are so big? Brain when you make your new lamp, is it going to be longer than necessary or is there a chance you can make it like the one Arizona Video posted? It just seems beneficial no matter what light engine you use.

The projectors that use the lamps I am referring to have safety interlocks that won't allow the lamp to come on if the enclosure is open. I am not saying 'don't use the lamp', I am saying that I will not sell an unprotected halide to the community at large. It would be very irresponsible at this time to do so, especially considering that the people I have seen using these lamps are taking stupid risks. It isn't just a suntan BTW, it is a real cancer risk. Bare arc exposure = melanoma.

Short arc lamps may be in our future (as far as me retailing them) but there will be a lamp holder that protects from the arc.

The HSD lamp in that form factor has a very high cost and a 750 hour life. The ballasts to drive them are very very expensive. I have spent two months going over this with the manufacturers. It is actually easier and cheaper for me to get real short arc lamps with a 1.5mm arc gap. I have a source for those but I've yet to find someone to make the proper ballasts.

The lamp I am getting made now is much smaller than the S400. 24mm diamter x 150mm length.

You will find that as the arc gap shortens then the voltage for the lamp will be less too soon you have a lamp with a high current to voltage ratio which will require a special transformer to be made. I would try to make it a 110 volt lamp and run it on standard S51 ballast. Or a slightly modified ballast.
I know of no light source besides the HMI types that use low voltage/high current ballast. This means custom made and more money. Go cheep.

Well, I don't know... I trust Brain has done his homework here. I don't know anyone else with the resources to do this so, what ever he figures. I'm glad to know he feels a sense of responsibility to the community.