beamshape&hotspot:vertical vs. horizontal filament

While searching for some nice bulbs for an upcomming project I found some bulbs with a horizontal filament and others with a vertical one. My crappy drawing might make it more clear:


Now what are the advantages between these two? Is it easier to focus, smaller hotspot? Anything else?
Advantages, disadvantages?

Thanks for any clues. /ubbthreads/images/graemlins/wink.gif

Klaus.

Re: beamshape&hotspot:vertical vs. horizontal fila

Klaus,

This is a complex issue that, to date, has very little empirical evidence suporting conclusions of any sort. The problem has been lack of directly comparable Horizontal/Axial filament bulb pairs.

Still, I think it depends to some degree on the reflector you're using. The only common finding has been that large H filaments result in bi-lobe or oval hotspots whereas A filaments of any length result in circular spots. Also, you will always see the projected image of the support wire on one side of the beam with A filaments.

I have a Vector 2MCP with a 6" reflector and A and H filament bulbs so I will take some beamshots. I also have some A filament bulbs coming for Aurora so I will have the opportunity to test with a deep 3" reflector.

Wilkey

Re: beamshape&hotspot:vertical vs. horizontal fila

Wilkey,

Looking at WALAMP.com and the specs what's the diameter and what's the length of the filament got to do with the end result of the hotspot?

WA01160 has that bowtie hotspot, would WA01316 be about the same?

Thanks!
V!~!~!

Re: beamshape&hotspot:vertical vs. horizontal fila

V,
The longer the filament, the more prounced the bowtie or bilobe. I'd guess the diameter of the wire affects the efficiency and output characteristics in some way.

Anyway, here are some pictures. The host is a Vector 2MCP spotlight. The axial bulb is the one that came with it. You can see the support wire at about 11:00 o'clock. I took two photos of the horizontal filament automotive H3 bulb. One is rotated 90 degrees from the other. You can also see that the two filaments are about the same size and the filament centers are at about the same LCL (light center length) so there should be no focus differences.



Wilkey

Re: beamshape&hotspot:vertical vs. horizontal fila

SO what we need is a I filament, where the support wire (and conductor) goes up the middle of the filament. It would have to withstand a lot of heat.


Daniel

Re: beamshape&hotspot:vertical vs. horizontal fila

Thanks for the pictures.

Judging from your pictures the axial filament setup produces a nicer hotspot, no oval beam. /ubbthreads/images/graemlins/grin.gif

/ubbthreads/images/graemlins/thinking.gif

Re: beamshape&hotspot:vertical vs. horizontal fila

Where do you buy axial filament H3's for 6 volt spotlights?

Bill

Re: beamshape&hotspot:vertical vs. horizontal fila

It rather depends on the reflector size vis-a -vis the filament size. If the filament dimensions are small, then the posted beam shots are close to what one sees. The axial filament (filament axis parallel to reflector's optical axis) produces a single round spot that is quite soft edged. A transverse filament produce a still round hot spot but with an oval secondary hot spot that is dimmer than the main, round hotspot. In a small reflector The axial filament tends to produce a rather wide beam. The transverse filament is much better in this case. The solution? A square filament! Some that I know are: Osram HLX 64265; HLX 64616 and WA 01165. If you know of others, please let me know!!! /ubbthreads/images/graemlins/grin.gif I use the 64265 in a Streamlight #45913 spot assembly and it produces a rounded corner square spot. Very little stray light. H3 bulbs have transverse filaments. Those with axial filaments cannot be called H3s.

Re: beamshape&hotspot:vertical vs. horizontal fila

Would that 45913 spot assembly have to do with the LiteBox.

Bill

edit. I just did a Google, and answered my own question. Yes it is a LiteBox assembly. How did you change out bulb?

Re: beamshape&hotspot:vertical vs. horizontal fila

Strictly speaking I think Axial is much better to Horizontal just due to the fact that most of the reflectors we are using in flashlights are for a point source of light. Who really wants these 2 weird lobes anyhow? I know if my vector the stock A bulb looks way better than any H3 replacement bulb I've used because the car H3 is ALWAYS Horizontal. Oh yeah, A is more rare, because it is harder to make and is therefore more expensive.

Re: beamshape&hotspot:vertical vs. horizontal fila

"A" bulb? Who sells them? Go through Vector? Are we talking a 6W or 12W bulb, or are they both available?

Bill

Re: beamshape&hotspot:vertical vs. horizontal fila

Bill,
I know of no accounts of anyone ordering replacement bulbs from the Vector website. They are about $5 a piece and $5 a piece for shipping. $10 is a lot of money to find out if they are the A bulbs or if they are the same H Vector-branded bulbs found retail. I am not willing to drop money to find out.

Phy,
I agree with your observations regarding H versus V spots. I don't understand what you're saying about square filaments though. I'm looking at one of my 64625HLX and filament looks like a pack of chewing gum. A flattened shoe-box shape that is rectangular in all dimensions.

I think another way to think about the spot shape is to think of it not as a result of the filament orientation, per se, but rather a function of the deviation of the filament geometry from the one-dimensional focal point and the resulting defocus. In other words, sufficiently large H filaments create the bilobe because the ends of the filament drift off the focal point laterally extending the hotspot in that plane. Large A filaments create a fuzzier but rounded hotspot. This is borne out by careful measurement of the hotspots for both bulbs above. The diameter of the A hotspot is greater than the narrow diameter of the H bulb's spot. To me, this implies that the smearing occurs in coaxial cylinders around the axis of the filament.

Wilkey

Wilkey

Re: beamshape&hotspot:vertical vs. horizontal fila

I have found the horizontal (H) and verticle (axial = A)filaments in the standard 12v, 10watt G3? G4? bulbs from the big box stores which will fit in Carley's PR adapter. Neither one throws a good beam with the Mag reflector - see Ginsings comments. The rather long filament required for 12v just doesn't work unless you have a reflector designed for it like the one used in the MR-16 lamp. A 'V' shape might work - sort of combining the disadvantages of both H & A but minimizing them. I have seen it used in some bulbs....