1920's Box Spots now MR-16 Fixtures


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So, as soon as the other six can be found, I own three or more lot numbers or brands of plano convex box spot. This by way of many brands and even yoke verses stand mount. One even with an interesting Fresnel lens I have never seen before. Front side a Fresnel, rear side as if a wide flood PAR 64 lamp in surface.

Anyway, these fixtures normally suited for a 400G-FL lamp, I"m modifying for a 20w/12v Ushio BAB/FG lamp Not my optimum choice in shooting for a 45 degree angle and this only giving me 36 degree, but it should still focus sufficiently as a theory. If a 36 degree instead of 40 degree lamp is not sufficient, I still have lots of at least 40 degree choices. This before I move up to the BAB/60 series of 60 degree lamp type but having potentially lots of spill.

Anyway, as above, the 1920's fixtures have had their medium screw bases removed and Gimbal mount MR-16 lamps installed in their places. These jacked up to the bench focus height and centered upon the filament as necessary.

Kind of cool project - this similar to what I often do with large wattage Fresnels in making them LED or much less wattage fixtures, except in this case they are for my living room. I want low voltage MR-16 in washing the ceiling.

Anyway, below is the first two fixtures wired. First set of photos is for the Fresnel version that was stand mounted an Fresnel lensed. Still in all ways a box spot but definately much older by way of very unique lamp base no longer sold and in all other ways just seemingly older. The next set of pootos is the version I have four of all the same and I estimate from the 1940's thru 1950's. Possibly earlier but just got that feeling they are not as old.

Some bench focusing to do but it in theory should work. Than again they might not work.

Will a MR-16 lamp optimized for focus on a 4.1/2" lens, both Fresnel and PC provide a similar light to that of the 400w flood lamp the fixture was designed about? What will a MR-16 behind a 4.5x6.5 PC lens, and a unique fresnel lens do?

Have not plugged them in yet. Given nobody else has ever done such a thing, before I post the answers, let's get some theories here.


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The following is what the normal lamp for the fixture would look like - lens removed.

Any debate or theorizing of what a MR-16 behind the lens (both types) will look like in this situation?


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CB Mods
This is one of those questions I feel like I should be able to answer, but can't quite figure it out.

Originally, this fixture used a lamp that was in effect a point source. Later fixtures used a spherical reflector to gather the lost light and redirect it through the source. With all the light striking the lens either from the source or re-directed through it, all the rays of light were coming at the lens from the same focal point.

However, an MR 16 uses a parabolic reflector. In this case, the light comes not only from the point source of the filament itself, but from the light redirected by the parabolic reflector. Now, I would assume the filament of the MR 16 you selected is not at the focal point of the reflector, as this would be a mini beam project and I'm not even sure if those exist. What I don't know, and what would help, is the angle of the MR-16's you chose for this project. Either way, with the MR 16, the rays of light are focused at two different points, being the point source that is the filament, and wherever the focal point of the reflector is.

In the mean time, I do offer this hypothesis: the beam of these box spots will still be focusable, however, I would suspect the final beam will be wider than the original equipment.

A thought on that Fresnel: That pattern reminds me of the Fresnel lenses designed to spread the light into an oval. However, that does appear to be a rather early lense, particularly in the case of the very large central "bulls eye" and the uneven rings, neither which have I seen in other Fresnel fixtures that I can recall.

Another thing I have been wondering, is a box spot really called a box spot because it is, infact, shaped like a box? If the box was changed to a cylinder, wouldn't it no longer be a box spot? Seems to simple for theatre.:)

In addition, in all the Kliegl, Altman and Strand literature on line, why is it that I cannot recall seeing a Fresnel box spot, but rather only PC versions. Did the other major manufacturers of the day offer Fresnel box spots, and if so why have I yet to see reference to this. Clearly, Fresnel box spots do exist, as I have pictures I have saved off ebay showing box spots with both Fresnel and Step Lenses, in addition to PC lenses, but where they sold that way, or was the Fresnel a later addition to update older equipment?
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CB Mods
I was thinking today about the difference between the Fresnel and the PC with the MR 16 source. Based upon my explanation from yesterday, I would think that the Fresnel will have a more conventionally smooth and even beam with the MR16, but will likely be wider in spread than with the original lamp. The P/C might have an uneven field more like the MR16 that is its new source than the field it would have had with the original lamp. PAR lamps, especially the smaller ones, have rather uneven fields. The MR16 might be wild-bright, but the beam is very uneven. Right now, as I look at the MR16's above my desk, there is a center "hot spot", surrounded by a less intense, but still identifiably focused, wide-angled field of light


CB Mods


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Finally got the chance to power up my first two fixtures of these type. I was using an Ushio lensed BAB lamps which are only 36 degree but all I had in stock at work.

In answer to will it work, yep, it works in a similar way to the old lamps work by way of a sort of harsh light effect but one that's period as it were in doing so. Very similar in fact except that the color temperature is much higher and the fixture efficiency was boosted.

So first I tried the PC lensed fixture. On paper photometrically, given the approximate center point of the filament on a 400G/FL lamp designed for the fixture, it's a 45 degee angle if the filament of the MR-16 is placed in the same position in a reletive sense. In other words, one wants a 45 degree beam spread by the math and I did do the math and even lay it out in drafting it up.

The 20w BAB lamp is a bit under powered in comparison with what I remember of a 400w lamp but that's the design intent to be not as bright.

More important beyond intensity is what each of the two Fresnel and PC lenses did when a MR-16 lamp was powering them up.

The PC lens was tried first. In spot position, stridations from the reflector upon the beam image were miserable and clearly showing. This would be a really bad choice for a lamp/lens. IN flood position, it wasn't that bad all together. Towards the edges of the beam there was still stridations from the reflector but it was a fairly even beam other than this and a frosted gel would cover for this. I also could not get the beam to bench focus with a hard edge I should be able to. This was possibly due to the beam angle of the lamp used, or perhaps being not so centered. This lamp, lens and position however was the closest to doing an honest hard edge and flat field focus however. Just about there in being as one would expect with a PC lens fixture. That is an MR-16 lamp powering up a antique PC fixture.

The Fresnel lens was miserable in all ways. Spot position was less bad than flood position but overall, you could while not seeing clear stridations, there was absences or shadows in the beam that got worse the more you sent the lamp towards flood position. It will be a tremendous savings of money to me in not having to replace all lenses with a Fresnel, but who knows once I do the 40 degree, much less 60 degree lamps what will work best. This by way of soft image verses hard PC image.

The grainy image of a Box spot I remember was definately gone in both cases due to the change of lamp. Much more like a modern stage light instead of antique effect.

What's learned... First if it's a 45 degree fixture, the 36 degree reflector lamp seemingly is not optimal for use in it. I have some GE brand 40 degree lamps on order and will try them. As a theory I might in flood position for the PC lens be able to get really close in flood position to a good tight bench focus beam with a hard edge. This in between spot and flood should also work theoretically very well.

Otherwise in this experiment, there is BAB/60 lamps available with a 60 degree beam spread. If I cannot get a bench focus off the 40 degree GE lamps, the next choice is something from Ushio, Osram, or Dura Lamp that is available in 60 degree. Also, given the fixture is enclosed and lensed, a lensed version of this lamp is optional in a won't hurt but won't be needed type of way.

That's part two of this experiment. What will the closer to the beam angle of the fixture 45 degree, by way of MR-16 lamp, 40 degree or 60 degree lamps do in the fixture?

Overall, if you have to, and in doing so, the PC lens with so far the MR-16 lensed BAB lamp with 36 degree beam angle is not that bad in a classic 1920's box spot with PC lens in flood position.

There is our answer, it's a promissing concept this more efficient lamp within a antique fixture.
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CB Mods
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Can you post pics of the Fresnel/Par weird lens by itself...it intrigues me.


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What a cool project ship. I've got 4 old Century Strand Fresnels in the garage (1950's?) some day I'm going to build my dream rec-room and the fresnels are going in there. I would love to see a picture of what it's like when the project is done.


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[[excellent... the system randomized my slide show of photos in their order.

Image #6 is one in spot, #3 is two in flood, #2&5 are four/five of the MR-16 flood with Fresnel lens.
Image #12 is six in flood, #6 is seven in spot, #13 & 11 is image eight & nine below described - the MR-16 spot with PC lens

Image #9 is image nine flood postition, #7 & 8 are in spot of the photos #10 of the line voltage 400G/FL lamp with image #1 below showing my bench focus technique - bench vise focused on a white screen.]]

Ok, went back and did another bench focus with photos. This time on my bench vise with a white drop 8' distant from it.

First in the photos is the Fresnel lens PC fixture with Ushio 20w/12v 36 degree BAB lamp. Note, it can use a bit of adjustment to it's bench focus centering.

Flood was about 7' field angle with stridations and un-even beam. Spot was 4'-6" field angle which while spotty, a bit more even.

Second set was the PC lensed PC fixture with the same lamp. Note, as far as I can tell LCL of the lamp to the lens is 45 degrees. I don't know for sure what exact lens is in these units.

Flood was 5'-4" field angle with a hard edge to the beam within about three inches while in flood. Stridations of the reflector seemed to for some unknown reason clear up as the lamp heated up. Field was fairly even and decent after it warmed up. Spot was 3'-6" and showed the stridations in a harsh way from the reflector lamp. Bench focus as far as alignment to the lens was also just a bit off but corrected I believe in the last photo.

Finally I wired up one of the origional 400G/FL lamps to the fixture and bench focused it. Seems as if this one was a bit out of alignment due to a serious double image I find curious. Beam was not able to get a tight bench focus hard edge and overall not so even or nice.

Flood measured 7'-0" and had stridations theoretically from the filament. Spot position while it had less stridations at 4'-6" was even more spotty in image by way of a total lack of flat field.

Still yet to try the 40 degree from GE and 60 degree BAB lamps out of Ushio, Osram and Philips. My theory is that given I only needed about 3" dia. more focus room for a good hard edge, the 40degree sounds promessing.

(TBA a report on my Kliegl Dynabeam. Service calling it at work to become working lobby sculpture. This has got to be one of the most cool follow spots I have ever worked on. Just wait until the photos of the flip out flood lens gets shown. Fascinating to an extreme. Flip out shield to cover the iris etc. Working 3,000 Watt incandescent lamp that does not have a brand name but does have 4/1/68 written on it. This on a fixture that's of unknown date but someone signed the back of it as of 1963. Origional gel - think it's Roscoline but could be a fore runner to that, and in absolute mint condition by way of working & paint. Just finished re-wiring it and cleaning the top half of it.)


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Finally got my 40 and 60 degree MR-16 BAB lamps in and had a chance to play test what they would look like inside a box spot as opposed to the 36 degree beam spread BAB lamps normally available that didn’t do such a hot job.

First observation is that luminous output on the 36 degree lamps was more overall and more similar to that of the 400w/120v lamp usually used in the fixture - a 400G/FL. As above however, there was a specific lack of ability to bench focus to a hard edge and the beam was not able to get a even wash to say the least.

Following are the photos from a GE #20814 BAB (Q20MR16C/FL40̊) lamp that is one of the only 40 degree lamps on the market, and an Ushio BAB/60/FG lamp (12v 20w WFL60̊) #1000004.

Theory was that given a photometric 45̊ angle between filament and lens, that if one got closer or exceeded that beam angle, one would gain the benefits of an low voltage MR-16 lamp in use and still retain the photometric beam characteristics of the non-reflector included incandescent lamp it was design for. This with both PC and Fresnel lens. Un-measured is what exact PC lens is in use with the fixture, given it was the same in all tests this won’t matter as much but I”m noting between both white/blue and green, Altman still offers eleven 4.5" lenses of all types of beam spread, though not the 4.5" Fresnel lens which could be acquired elsewhere.

Theory sort of worked but not really. Was never able to get a hard edge beam similar to that of the 400G/FL lamp. At no point was I in bench focus mode able to pull the outer field angle ring (I measure from below) into that of the beam angle ring of light. In fact, that distance was similar no matter what lamp was used. This could theoretically be a question of adjusting the focus distance between filament and lens, or given there is only so much room inside the fixture something that is not possible to get a hard edge on. The crossing over effect of beam spread is theoretically a problem when it needs to hit a lens this close in proximity. Given a soft edge would be more my preferred end result, this while notable is not as much a problem.

On the specs, the Ushio 60̊ lamp is what I would choose. The 40̊ GE lamp for some reason had much too harsh a reflector when projected thru either lens type at a close distance to be useful as other than pattern effect. In other words, in all situations, you could clearly detect a effect from the reflector - specular reflector image reproduced on the tarp which was placed at the same bench focus distance as above. This brand of lamp is kind of throwing off the science of what either does but by way of lamp brand/ways to do a reflector it did play a major role below. Not to say that a GE lamp wouldn’t be just fine in a track light but a 40̊ BAB lamp inside a Box Spot would be a really poor choice if one wanted a useful beam of light for more than just effect.

Datta on beam spread to go along with the photos:
40̊ Lamp in PC.
Spot position 4'-2"
Flood position 5'-2"
60̊ Lamp in PC.
Spot position 3'-10"
Flood position 6'

(The above in the 60̊ lamp was much more even in wash of light but still would not bench focus to a hard edge.)

40̊ Lamp in Fresnel
Spot position 5'
Flood position +11'
60̊ Lamp in Fresnel
Spot position 4'-7"
Flood position 8'

In the data above, I was measuring approximate field angle where the beam output was about 50% or had a defined ring for field as opposed to beam angle. One would think that in a Fresnel, that the 60̊ source, that the beamspread would increase. Not persay given the useful light hitting the lens and what the lens than does with it. In this case bench focus of filament to lens might play more of a role - this even if the reflector on the MR-16 played more a detrement to the beam image.

Note also that measurements are not by way of photometer just best measurement across the beam I could.

The beam of the PC lens makes a bit more sense & will be interesting to compare with that of the 36 degree lens. Didn’t above note the field angle of the 36 degree but I did measure it. As soon as I can find that note pad... Still end result is that the 60 degree lamp while it won’t bench focus by way of reflector type did a much better job of putting out a beam of light than other beamspreads. That’s what I was looking for - this even if I’m loosing a lot in output over that of the smaller beam angles. Not such an efficient lamp in the end for output, but still a 20w/12v lamp instead of 400w/120v lamp is a good thing or concept. Easy enough to do 75 or more in wattage if it were needed.

Not a perfect replacement for the hard edge and even grainy yellow beam from a PC, more just an experiment of can it be done and what would it look like. This much similar to the question of if one could do a say low voltage MR-11 or capsule lamp inside a Leko, how well would it work?

As normal for this post, Control Booth’s system scrambled the photos.

As presented:
Image #1, PC 40̊ Spot
Image #2, PC 60̊ Flood
Image #3 PC 60̊ Spot
Image #4 PC 40̊ Flood
Image #5 PC 40̊ Spot
Image #6 Fresnel 40̊ Flood
Image #7 Fresnel 40̊ Spot
Image #8 Fresnel 60̊ Flood
Image #9 Fresnel 60̊ Spot


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