# WW2 Carbon arc vs skytracker spotlights



## kuna (Oct 14, 2012)

Hey I have a question about the 800 million CP ww2 searchlights. Every site that advertises these things says that the beam can be visible 20 to 30 miles away. I find this hard to believe because the 4 beam skytracker spotlights with 2-4kw per lamp only go out to about 5 miles under good conditions.


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## AnAppleSnail (Oct 14, 2012)

Light goes until it hits an object. Note that they say, "Can be." In NYC you wouldn't see them from more than 20 blocks away. In BFE Alaska, it might be visible for 30 miles. Finally, searchlights are meant to find and then highlight it. They aren't necessarily meant to make pretty columns of light.


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## BVH (Oct 14, 2012)

They absolutely are visible from 20+ miles. I owned one and I had occasion to drive to a buddy's work site with his 60" running and I clearly saw it from 23 miles distant. The intensity of the beam is far, far greater in the CA than in any of the Sky Rose type lights. At 73 Volts DC to the carbons and 150 Amps of current, they are pulling 11KW. Plus the 5' mirror does a far better job of collecting and focusing the light than do the small Sky Rose lights.

Those of us in the CA League refer to Sky Rose lights as Spotlights, not searchlights.


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## The_Driver (Oct 14, 2012)

hint hint: look at BVH's profile picture :devil:


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## kuna (Oct 14, 2012)

BVH said:


> They absolutely are visible from 20+ miles. I owned one and I had occasion to drive to a buddy's work site with his 60" running and I clearly saw it from 23 miles distant. The intensity of the beam is far, far greater in the CA than in any of the Sky Rose type lights. At 73 Volts DC to the carbons and 150 Amps of current, they are pulling 11KW. Plus the 5' mirror does a far better job of collecting and focusing the light than do the small Sky Rose lights.
> 
> Those of us in the CA League refer to Sky Rose lights as Spotlights, not searchlights.



Yea I know the difference between spotlight and searchlights its just that people usually refer to the old carbon arcs as searchlights. The spotlights I was talking about usually have four 2 or 4kw xenon short arc lamps and are about 200 million candlepower each. An example: http://www.youtube.com/watch?v=et-n3nwOfzY . Its just that while those are very bright you will have a hard time seeing the beams more than 5 miles away on a clear night so I have a hard time believing you will see a ww2 searchlight 20-30miles away as claimed on every site that advertises them lol

Edit: They are actually 200-310 million candlepower per lamp depending on wattage. So you are sure you would be able to see a ww2 searchlight from 20 miles and it would be more than just barely noticeable?


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## BVH (Oct 14, 2012)

I am familiar with the different arrangements of the spotlights. Assuming the searchlights' mirror is in good shape, (which my friends' light is) as I mentioned I've easily noticed his lights' beam from 24 miles. It's not like being up close to a lasers' beam but it's clearly visible. I would suspect the beam divergence is greater in the spotlights so only at best, 20 to 25% of the focused candlepower of the spotlight into a wider diverging beam equals lots less distant viewing mileage. Especially in a city environment, the spotlights wash out quickly. I'd take the stated candlepower of the spotlights with a grain of salt. Spectrolabs' NightSun uses a 1.6KW lamp and projects a 4 degree beam at tightest focus and is only rated at 40,000,000 CP. Even at twice the power, and possibly a tighter beam, I don't think you're going to see a 5 - 6x's increase in CP.

EDIT: Just looked at a new 4KW on Ebay. Shows a beam angle of 9 degrees. That's pretty much a "flood" beam, not a spot beam.


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## kuna (Oct 15, 2012)

BVH said:


> I am familiar with the different arrangements of the spotlights. Assuming the searchlights' mirror is in good shape, (which my friends' light is) as I mentioned I've easily noticed his lights' beam from 24 miles. It's not like being up close to a lasers' beam but it's clearly visible. I would suspect the beam divergence is greater in the spotlights so only at best, 20 to 25% of the focused candlepower of the spotlight into a wider diverging beam equals lots less distant viewing mileage. Especially in a city environment, the spotlights wash out quickly. I'd take the stated candlepower of the spotlights with a grain of salt. Spectrolabs' NightSun uses a 1.6KW lamp and projects a 4 degree beam at tightest focus and is only rated at 40,000,000 CP. Even at twice the power, and possibly a tighter beam, I don't think you're going to see a 5 - 6x's increase in CP.
> 
> EDIT: Just looked at a new 4KW on Ebay. Shows a beam angle of 9 degrees. That's pretty much a "flood" beam, not a spot beam.


Yes its true that the old carbon arcs have a great beam with almost laser like divergence. The four beam skytrackers aren't as good but their not to bad either. The video I linked can show you if you haven't seen but you probably know what Im talking about lol. Im only asking because Ive seen such amazing distances posted for the carbon arc such as 30 miles that I wanted to check with someone whos knows for sure. Ive lurked on this forum for quite a while and I knew you would have the answer  I guess the wider beam(60") with more candlepower and lower beam angle really helps.

Edit: Your sure it was 24 miles as the crow flies? If so that's amazing.


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## BVH (Oct 15, 2012)

kuna said:


> Edit: Your sure it was 24 miles as the crow flies? If so that's amazing.



Yes. If I remember correctly, my CA beam angle was 1 or 1.5 degrees. That makes a huge difference when compared to a 9 degree beam - even if the CP was the same.


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## kuna (Oct 17, 2012)

BVH said:


> Yes. If I remember correctly, my CA beam angle was 1 or 1.5 degrees. That makes a huge difference when compared to a 9 degree beam - even if the CP was the same.



Lets say that someone took the carbon rods out of a 60" CA and replaced them with one of those 15kw xenon short arc lamps. Do you think you would get a brighter beam with more CP? I believe that a CA has efficacy of around 17 lm/w while a xenon arc has a little more. Would you get say 1-1.2billion cp vs 800 million with just the CA? Btw I know this is speculative since I dont think anyone tried this but it would be a cool experement :laughing:


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## BVH (Oct 17, 2012)

There's a few variables to consider. First, there is/was a company doing that to the old lights. "They" rated them at 1 Billion CP. The Dominator, I believe it was called. If the point source of light in the Dominator bulb was the same size or smaller, and the Lumens were the same or more, than I would say yes, it would have a brighter beam/higher CP. But if the point source of light was larger, then no telling what the result would be. Maybe more light produced, but not as sharply focused so less CP. But to generally answer your question, if all factor were the same except the Short Arc produced more Lumens, then the resulting CP would be higher.


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## kuna (Oct 21, 2012)

BVH said:


> There's a few variables to consider. First, there is/was a company doing that to the old lights. "They" rated them at 1 Billion CP. The Dominator, I believe it was called. If the point source of light in the Dominator bulb was the same size or smaller, and the Lumens were the same or more, than I would say yes, it would have a brighter beam/higher CP. But if the point source of light was larger, then no telling what the result would be. Maybe more light produced, but not as sharply focused so less CP. But to generally answer your question, if all factor were the same except the Short Arc produced more Lumens, then the resulting CP would be higher.


 Alright since you have good experience with the CA do you think there would really be such a big difference if you were to place a 60" CA next to a 4 beam skytracker producing nearly 300 million CP per beam? Im talking about how it would look from say 1.5-2 miles distant. Everyone ive seen talking about the CA's always say there is


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## BVH (Oct 21, 2012)

I don't know how to make myself more clear but I'll try. If placed right next to each other and you were 1.5 to 2 miles distant and - the lights were in a typical city environment with it's typical ambient lighting condition with street lights, business lights etc., then you would see a huge difference. The CA would stand out like a huge, thick laser beam and the tracker beams would be visible but less than 30% as bright. A very, very marked difference would be visible. There is no comparison between the two. Its too bad there isn't a CA near you so you could experience it. If you're ever in the Los Angeles area, I can arrange for you to see the best conditioned, most original 1942A CA in the world working.


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## kuna (Oct 22, 2012)

BVH said:


> I don't know how to make myself more clear but I'll try. If placed right next to each other and you were 1.5 to 2 miles distant and - the lights were in a typical city environment with it's typical ambient lighting condition with street lights, business lights etc., then you would see a huge difference. The CA would stand out like a huge, thick laser beam and the tracker beams would be visible but less than 30% as bright. A very, very marked difference would be visible. There is no comparison between the two. Its too bad there isn't a CA near you so you could experience it. If you're ever in the Los Angeles area, I can arrange for you to see the best conditioned, most original 1942A CA in the world working.



Sounds good. I just had a hard time believing that these carbon arcs could really be that much more bright. It never made sense to me that they could be seen from so much further when they have similar beams. 300 million cp 20" beam vs 800 million 60" beam. Im gonna assume you have seem both of these in action. I guess im just biased towards these 4 beam skytrackers because they are the reason Im in this hobby because they were awesome to see up close and far away. Ive seen them on many occassions from 1.8 miles and 3.2 miles away and at 1.8 miles they were easily seen but at 3.2 miles the beams themselves were not that easily seen but not absent at the same time if you know what I mean lol. Now, on the other hand I saw one of you're posts about a 4 BILLION cp spotlights from the 1930's(iirc). Now I have no Doubt that a 40" beam at 4billion cp will really be seen much brighter than any 4 beam skytracker but at the same time I really doubt there could be a true 4 billion cp searchlight from that era but I dont know much about that light. Do you have any stats on that light such as beam diameter? and I assume it was a CA to produce that intesity. Sorry for long post haha


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## BVH (Oct 22, 2012)

A very key reason for the huge difference in brightness is that the beams are _not_ similar. With the CA, you have 400,000 or so Lumens focused down to a 1 to 1.5 degree beam while all the data I see on the trackers says they are 9 degree or larger beams and the 4KW units are producing about the same lumens.

I have no stats on the 4 Billion CP advertising light. Just the original press photo. Look at the size of the ventillation/cooling shaft. With a huge volume of cooling, there had to be a very bright and very hot light source.



kuna said:


> Sounds good. I just had a hard time believing that these carbon arcs could really be that much more bright. It never made sense to me that they could be seen from so much further when they have similar beams.


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## AnAppleSnail (Oct 22, 2012)

kuna said:


> 300 million cp 20" beam vs 800 million 60" beam.



The throw of a light (Intensity of its beam) is based on the ratio between the source size and optic size, and linearly scaled with output. So if I have two identical-output light sources, and make one half the size, I greatly increase throw. Similarly, tripling the optic size greatly increases throw. Finally, increasing output while increasing size quickly runs into problems of making optics that are big enough. Carbon-arcs make a very small, intense point of light. This, combined with a VERY VERY big dish, about the size of most cars, gives a tight beam.



> ...I really doubt there could be a true 4 billion cp searchlight from that era but I dont know much about that light.



Why? Optics laws have been known for centuries, and arc-lamps for many decades. Heck, the fastest plane in the world was built with slide rules...


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## BVH (Oct 22, 2012)

Thanks for jumping in Apple! You explained in much more technical terms than I did.


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## sven_m (Oct 22, 2012)

In "The outdoor use of lasers and other high intensity light sources in relation to air traffic safety",
a paper from the dutch TNO (applied scientific research),
two lamps with 60" carbon arc mirrors were measured.
One with real carbon arc and one with an Osram 12kW HMI bulb (said "Dominator").

Lux were measured at 25, 50, 75 and 100m, then extrapolated, and the result was
- 60" with carbon arc: ~ 129,300,000 CP _(edited, I wrongly wrote 201,600,000 at first)_
- 60" with 12kW HMI: ~ 140,200,000 CP _(edited, I wrongly wrote 209,900,000 at first)_

(It's on p. 25 and 27: they printed numbers for special distances and I calculated CPs from that)
_
Edit: ah, here's a link to the PDF_

I don't know what type of HMI lamp was used and I don't know the illuminance of a carbon arc,
but these HMI lamps have an arc length at about 25mm AFAIK, and I guess main emphasis of these
HMIs is not on arc illuminance, so that even brighter arcs are possible and would increase CPs...

Learning and calculating with arc illuminances might be a bit tricky, as we don't know the quality of the reflector curve, though?
(can a huge arc for a given reflector be better than a very small one, that is, if the reflector seems only partially illuminated for the latter when looking from the target?)


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## kuna (Oct 22, 2012)

sven_m said:


> In "The outdoor use of lasers and other high intensity light sources in relation to air traffic safety",
> a paper from the dutch TNO (applied scientific research),
> two lamps with 60" carbon arc mirrors were measured.
> One with real carbon arc and one with an Osram 12kW HMI bulb (said "Dominator").
> ...


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## sven_m (Oct 22, 2012)

kuna said:


> Are they saying that the carbon arc is really only 201 million candlepower? I cant really infer anything differently based on the fact different distances were used and 201 was the average.



They didn't give these very numbers, but I calculated them from their diagrams: They gave exact numbers for e.g. 680 Lux at 436m (from their calculations in turn from the values for 25...100m which were not printed)
Ha! But I confused numbers and calculated wrong. I'll update my post, too.


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## kuna (Oct 22, 2012)

AnAppleSnail said:


> Why? Optics laws have been known for centuries, and arc-lamps for many decades. Heck, the fastest plane in the world was built with slide rules...



Well in theory of course its possible but to do such a thing you would need like an 80" reflector and probably around a 35kw+ CA or XSA lamp at perfect focus to achieve that. I have no idea on the stats of that 4 billion cp spotlight mentioned in a thread by BVH so I cant make any judgements on it. And talking about the size of optics/size of light source increasing throw I know all about that ive been interested in this hobby for years and also interested in lasers. Ie a LED cannot compete with a laser in throw because the laser has a much smaller, intenser light sorce that allows it to be focused into a shaper beam. Same thing when comparing an hid bulb with a xenon short arc. You would need a larger reflector in a HID lamp to achieve the same throw in a XSA lamp of the same output.

Edit: Sven just saw your post and the 60" CA's produce even less than 200 million cp according to these people. Pretty suprising lol


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## BVH (Oct 22, 2012)

I dont put a lot of faith in their numbers. Spectrolab quotes btw 30,000,000 and 50,000,000 cp from the Nightsun which is only 1.6 KW & has a beam of 4 degrees. Theres no way an 11 KW CA with a 60" mirror is only going to produce 100,000,000+ cp. I would speculate that their measuring distance was hundreds or thousands of yards short of optimal focus.


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## kuna (Oct 22, 2012)

BVH said:


> I dont put a lot of faith in their numbers. Spectrolab quotes btw 30,000,000 and 50,000,000 cp from the Nightsun which is only 1.6 KW & has a beam of 4 degrees. Theres no way an 11 KW CA with a 60" mirror is only going to produce 100,000,000+ cp. I would speculate that their measuring distance was hundreds or thousands of yards short of optimal focus.



Yea I just checked out that pdf and they also tested one of the 4 beam skytrackers that I was talking about with 4kw bulbs and they have a beam of 2.6 degrees compared with the carbon arc beam of 2.8 according to that study lol. 

Btw the distance they measured at was 100 meters on a white wall. 

Oh and they only used like a 5mw green laser when it should have been more like 100mw


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## sven_m (Oct 22, 2012)

At first I found those numbers plausible because they seemed to converge in their logarithmic diagrams.
But on the other hand they don't exactly for the 60", and most important, they measured at no more than 100m.
Unfortunately indeed--it would have been quite an interesting comparison (some other, smaller 1-4kW searchlights were also included)


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## kuna (Oct 22, 2012)

sven_m said:


> At first I found those numbers plausible because they seemed to converge in their logarithmic diagrams.
> But on the other hand they don't exactly for the 60", and most important, they measured at no more than 100m.
> Unfortunately indeed--it would have been quite an interesting comparison (some other, smaller 1-4kW searchlights were also included)



Yes it would have been interesting to see how the other spotlights compared against the CA. I have to say that 140 million cp is probably a little bit too low for a 60" CA. I also found it interesting that the 4 beam skytrackers apparantly have a tighter beam than the CA's lol


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## BVH (Oct 23, 2012)

Went to the horses mouth to get this. Straight from the GE 60" manual. Beam degrees is 1.25 on the 60" CA and 2 degrees on the 36". I though as much as I do not remember seeing any significant divergence when running my light, even up to high cloud level. I remember one cloudy night landing the spot on a cloud and it looked almost exactly like the full moon was shinning thru a very, very thin cloud. I think you can pretty much hang your hat on the 800,000,000 CP as the lights had to pass rigorous testing to specs to be approved by the War Dept. Not like manufacturers today who can spout off with any numbers they want. (Unless selling to the military)


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## kuna (Oct 23, 2012)

BVH said:


> Went to the horses mouth to get this. Straight from the GE 60" manual. Beam degrees is 1.25 on the 60" CA and 2 degrees on the 36". I though as much as I do not remember seeing any significant divergence when running my light, even up to high cloud level. I remember one cloudy night landing the spot on a cloud and it looked almost exactly like the full moon was shinning thru a very, very thin cloud. I think you can pretty much hang your hat on the 800,000,000 CP as the lights had to pass rigorous testing to specs to be approved by the War Dept. Not like manufacturers today who can spout off with any numbers they want. (Unless selling to the military)



You're sure they were able to accurately measure the beam CPs back then? Not saying they werent as Im much more likely to believe that the ww2 carbon arc is 800 million true candlepower than the luxor hotel is 42 billion :laughing: Btw I was thinking before I even made this post that if you were to keep all things the same in the 60" CA except you were to push 20-30kw through the rods instead of 12kw would you get more cp in the beam or am I missing something like the arc will be bigger and wont focus the same or something. I know that the rods would obviously burn faster but I cant think of anything else that would really change. 

Edit: Oh yea btw that would mean the study that said the CA beam is 2.8 degrees is wrong if its really officially stated as 1.25. Wonder what else they did wrong? I personally think they should have done the test at more like 200 meters+ to get more accurate results.


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## BVH (Oct 23, 2012)

I don't think 200 meters would do it. 750 to 1500 meters maybe. Remember, the beam travels 5.7 miles at which point, you can read a newspaper (assuming a brand new mirror, which there are very few of) Think of all the extra heat created with the power level you cite. Chances are, the rods would vaporize extremely quick. How quick? I don't know but seconds probably. Next issue, heat-again. There's a heat shield about 1" from the arc. If the automatic rod fee system malfunctions and the + rod is not feed quick enough, the arc burns towards the heat shield. Guess what....Whatever metal the shield is made of, creates a beautiful blue-green flame for less than a minute then, your shield is gone. There goes $150 - if you can find a new one. Another issue, the positive rod automatic feed mechanism is insulated from the frame (ground). Pump that much more power into the system and the insulation would probably leak. The positive rods are 5/8" in diameter and the negatives are 1/2". There were some German CA's that used rods about 2.5" in diameter, I believe. Don't know what power they saw.


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## kuna (Oct 23, 2012)

BVH said:


> I don't think 200 meters would do it. 750 to 1500 meters maybe. Remember, the beam travels 5.7 miles at which point, you can read a newspaper (assuming a brand new mirror, which there are very few of) Think of all the extra heat created with the power level you cite. Chances are, the rods would vaporize extremely quick. How quick? I don't know but seconds probably. Next issue, heat-again. There's a heat shield about 1" from the arc. If the automatic rod fee system malfunctions and the + rod is not feed quick enough, the arc burns towards the heat shield. Guess what....Whatever metal the shield is made of, creates a beautiful blue-green flame for less than a minute then, your shield is gone. There goes $150 - if you can find a new one. Another issue, the positive rod automatic feed mechanism is insulated from the frame (ground). Pump that much more power into the system and the insulation would probably leak. The positive rods are 5/8" in diameter and the negatives are 1/2". There were some German CA's that used rods about 2.5" in diameter, I believe. Don't know what power they saw.



Seems plausible what you said. I bet those 2.5" diameter rods would be able to be pushed a bit more. I guess the best bet for a true 1 billion cp would be a 15kw xenon short arc and a large 60"+ mirror. Too bad nobody is working on a real powerfull searchlight to replace the old ww2's. I would love to see what people could come up with using todays technology  I guess the 4 beam skytrackers are here to stay. Not that they are bad or anything I happen to like them and they are pretty bright within a 1.5 mile radius but people would never know what an old ww2 ca was really like

I was thinking about how the ww2 60'' could be 800 million candlepower. It would have to have a lux reading of 80000 at 100 meters to be 800 million cp. This is slightly below direct sunlight which is about 100k-120k lux on a summer day with the sun directly overhead. Seems possible for one of these 60'' ca dont you think? Btw that study quoted 12900 lux at 100 meters for the 60''. Thats way lower than sunlight and probably a little bit too low for a 60'' ca at 100 meters I think. Another thing I noticed was all of the lights they measured were all way under spec compared their offically stated output which would suggest they were probably measuring wrong or had a faulty light meter.


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## LightSward (Mar 16, 2015)

kuna said:


> Hey I have a question about the 800 million CP ww2 searchlights. Every site that advertises these things says that the beam can be visible 20 to 30 miles away. I find this hard to believe because the 4 beam skytracker spotlights with 2-4kw per lamp only go out to about 5 miles under good conditions.



Aside from all the numbers, one thing I've noticed is for sure, when I'm operating my homemade:1,200 watt HMI 36" searchlight with 100,000 lumen output, 5 degree partially collimated beam, I can see it easily three to four miles in the city and more than ten miles out in the farmland near my home, depending on the direction I aim the searchlight. Live literally at the edge of town. The beam looks quite bright... However, when I fire up the 4,000 watt HMI at 380,000 lumen output in my 72 inch diameter Lord of Lights homemade searchlight with it's 5 degree partially collimated beam, it blows away the other searchlight. Math makes it seem like it would be about four times brighter and by itself, it looks the same brightness as the 1,200 watter, BUT, side by side, the 1,200 watt searchlight looks like it's NOT even on at all. The beam from the 4,000 watt searchlight is totally visible for ten miles in the city easily or more and twenty or more when I drive out in the farmland highways. Got nervous and drove back home to crowds of people driving my neighbors crazy. 

To sum it all up, the eye works differently than one would expect. Amazing how bright my 1,200 watt HMI searchlight looks by itself, but is totally drowned out by the 4,000 watt HMI searchlight when it's operating, yet within a few blocks, by themselves, each of the two searchlights look similar in brightness, until they're brought together, and then there's no comparison even at just a rough ratio of 3:1 wattage wise or a LUMEN output of roughly 4:1.

The two searchlights are roughly a 2:1 diameter size ratio and a 4:1 roughly mirror area size ratio, along with an arc ratio for the bulbs of: 2.3:1 for the arc measurements of: 23 mm for the 4,000 watt HMI and 10 mm for the 1,200 watt HMI.

Nothing scientific here, just personal experience working with my Las Vegas searchlight fantasy.:thinking:


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## sven_m (Mar 17, 2015)

BVH said:


> I dont put a lot of faith in their numbers. Spectrolab quotes btw 30,000,000 and 50,000,000 cp from the Nightsun which is only 1.6 KW & has a beam of 4 degrees. Theres no way an 11 KW CA with a 60" mirror is only going to produce 100,000,000+ cp. I would speculate that their measuring distance was hundreds or thousands of yards short of optimal focus.



...or the light was slightly defocused (perhaps even off-axis, which might be harder to detect), or the mirror was slightly deformed.



BVH said:


> I think you can pretty much hang your hat on the 800,000,000 CP as the lights had to pass rigorous testing to specs to be approved by the War Dept.



I also absolutely believe the 800 Mcd (at least roughly) for a GE 60".
Since the start of this thread I've found some interesting values for carbon arc luminance,
in 'Optical Society of America "Handbook Of Optics, Vol1, Pt4, Ch10 Artificial Sources", A.LaRocca, Ed2 (1995)',

- search light arc (rotating 16mm electrode, 150A, 78V) : 650 cd/mm²
- movie projector (rotating 14mm electrode, 160A, 66V) : 960 cd/mm²
- microscopy source (fixed 5mm electrode, 5A, 60V) : 150 cd/mm²

A GE 60" with 53" mirror (and 8" center hole), 80% rhodium mirror transmission, 92% glass transmission, by calculation would require 780cd/mm² in the arc itself. This matches just perfectly with the numbers above.



kuna said:


> I just checked out that pdf and they also tested one of the 4 beam skytrackers that I was talking about with 4kw bulbs and they have a beam of 2.6 degrees compared with the carbon arc beam of 2.8 according to that study lol.
> 
> Btw the distance they measured at was 100 meters on a white wall.



For spot lux, the beam degree (or spot size) is not of concern (depends on arc size and focal lengths). spot lux is only determined by luminance and diameter.

Originally, without knwing the 800 MCP value, I thought 100m distance might be o.k. because the carbon arc is so extraordinarly "huge" in comparison to a Xenon short arc.
But even their own diagram (page 27) leaves the question unanswered if the distance was long enough: The measurement points even don't line up in contrast to the other sources.
(And I was wrong about 436m, that value was not measured but only calculated).



kuna said:


> You're sure they were able to accurately measure the beam CPs back then?



Absolutely. In fact "CP" had been used so frequently, and the "candela" even had become an SI unit for these reasons.
It was the easiest to measure in former times. You only need distance and resulting lux (e.g. in comparison to a known source) to calculate it.
That's even the very purpose of "candela" aka "candle power": you can easily calculate resulting lux in a given distance, in turn.

"luminance" (cd/mm²) would have been a more reasonable SI unit, because it's the only unit which can be perceived intuitively, directly, by the human eye.
People usually have no idea what "candela" means at all (in contrast to all other SI units, like mass, time, length, etc.)
However, luminance is everything but easy to _measure_, and so the candela became SI unit.



kuna said:


> [...] if you were to keep all things the same in the 60" CA except you were to push 20-30kw through the rods instead of 12kw would you get more cp in the beam or am I missing something like the arc will be bigger and wont focus the same or something



I believe it might be possible to increase luminance only slightly. See the values I quoted above. With more wattage the arc would rather become bigger, that is, more lumens. But not hotter or denser. I guess you would need more gas pressure, or something like that, to achieve it.



kuna said:


> I guess the best bet for a true 1 billion cp would be a 15kw xenon short arc and a large 60"+ mirror. Too bad nobody is working on a real powerfull searchlight to replace the old ww2's. I would love to see what people could come up with using todays technology



The highest luminances I know are ~3000 cd/mm² (Osram XBO 2001W/HTP) and ~6000 cd/mm² (experimental Philips 0.3mm UHP).
This would result in about 3000 Mcd or 6000 Mcd, respectively, for a 60" searchlight.
But: the quality of the GE mirror would probably not be good enough to focus almost-point sources like these.
The carbon arc however is huge, about an inch, I guess.



LightSward said:


> "homemade 1,200 watt HMI 36" searchlight" vs "4,000 watt HMI at 380,000 lumen output in my 72 inch diameter Lord of Lights homemade searchlight " [...] Math makes it seem like it would be about four times brighter and by itself, it looks the same brightness as the 1,200 watter



What about just measuring lux in a known distance, have you ever tried? Then you would have at least plain numbers for CP (aka candela).
"usable spot size", lumens, etc. is certainly a different issue. Neverthelesse, CP is one of the basic properties of a searchlight.


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## LightSward (Mar 18, 2015)

sven_m said:


> What about just measuring lux in a known distance, have you ever tried? Then you would have at least plain numbers for CP (aka candela).
> "usable spot size", lumens, etc. is certainly a different issue. Nevertheless, CP is one of the basic properties of a searchlight.



I need to obtain a light meter I can trust...or download an app., I can trust. May be able to talk a friend into using his calibrated light meter. I've been reluctant to use CP because my beams aren't quite as collimated as I'd like them to be...probably about 5 degrees spread, hopefully less as I get rid of my orange peel texture from the reflectors.

I'm amazed at how things have changed for the advertising searchlights. Thirty or forty years ago, street lights were mostly incandescent or murcury bapor lighting and car headlights were much dimmer than today's design. Searchlights were easily seen back then, but now much brighter, perhaps big HMI searchlights will have to be made and designed to keep up with the ever increasing night light.


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## kuna (Sep 7, 2015)

LightSward said:


> Aside from all the numbers, one thing I've noticed is for sure, when I'm operating my homemade:1,200 watt HMI 36" searchlight with 100,000 lumen output, 5 degree partially collimated beam, I can see it easily three to four miles in the city and more than ten miles out in the farmland near my home, depending on the direction I aim the searchlight. Live literally at the edge of town. The beam looks quite bright... However, when I fire up the 4,000 watt HMI at 380,000 lumen output in my 72 inch diameter Lord of Lights homemade searchlight with it's 5 degree partially collimated beam, it blows away the other searchlight. Math makes it seem like it would be about four times brighter and by itself, it looks the same brightness as the 1,200 watter, BUT, side by side, the 1,200 watt searchlight looks like it's NOT even on at all. The beam from the 4,000 watt searchlight is totally visible for ten miles in the city easily or more and twenty or more when I drive out in the farmland highways. Got nervous and drove back home to crowds of people driving my neighbors crazy.



Wow, that is incredible. I remember seeing the thread with the original 1200W HMI 36" along with some beamshots, and being very impressed with that. I also remember a post where you said the beam was clearly visible from about 7 miles away, even with a picture of it attached. I don't remember if that was in the city or viewed from a more rural area, but impressive nonetheless. I'm gonna go look for the 72" build on here shortly  
A 72" searchlight with a 4000W HMI sounds incredible. I think that may be tied for the world's biggest searchlight along with a German-made searchlight that was made for a fair circa 1902. Can't remember the exact details on that except that it burned 2.5" carbons and is still used today occasionally on top of a town hall building around St. Louis. They replaced the original rod-feed mechanism with one from a 60" GE searchlight, so no more 2.5" carbon rods.

As a side note, last November I bough a 2kW Osram XL OFR off Ebay and am still not done gathering everything I need for the power supply. It's about 80% finished but it will probably take a few more months. It definitely takes a lot to build a 72" searchlight from scratch, very impressive. Can't wait to see the candela rating 



LightSward said:


> I'm amazed at how things have changed for the advertising searchlights. Thirty or forty years ago, street lights were mostly incandescent or murcury bapor lighting and car headlights were much dimmer than today's design. Searchlights were easily seen back then, but now much brighter, perhaps big HMI searchlights will have to be made and designed to keep up with the ever increasing night light.



I like the idea of that immensely  That's a great point you bring up about the extra light pollution today. It's particularly bad where I am, making the 20" skytracker beams wash out very quickly after 3 miles.


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## LightSward (Sep 9, 2015)

kuna said:


> Wow, that is incredible. I remember seeing the thread with the original 1200W HMI 36" along with some beamshots, and being very impressed with that. I also remember a post where you said the beam was clearly visible from about 7 miles away, even with a picture of it attached. I don't remember if that was in the city or viewed from a more rural area, but impressive nonetheless. I'm gonna go look for the 72" build on here shortly
> A 72" searchlight with a 4000W HMI sounds incredible. I think that may be tied for the world's biggest searchlight along with a German-made searchlight that was made for a fair circa 1902. Can't remember the exact details on that except that it burned 2.5" carbons and is still used today occasionally on top of a town hall building around St. Louis. They replaced the original rod-feed mechanism with one from a 60" GE searchlight, so no more 2.5" carbon rods.
> 
> As a side note, last November I bough a 2kW Osram XL OFR off Ebay and am still not done gathering everything I need for the power supply. It's about 80% finished but it will probably take a few more months. It definitely takes a lot to build a 72" searchlight from scratch, very impressive. Can't wait to see the candela rating
> ...



The 72 inch searchlight is incredible, but storage was a problem so I had to partially disassemble it to make room in my shop. I'm currently fitting the 50 inch Monster Searchlight with the 4,000 watt HMI light source. This design is based largely on the 60 inch WWII carbon arc searchlights. It has an incredible focal arrangement so the beam is well cilluminated and should go quite the distance. Just about ready for it's first test run.


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## kuna (Sep 10, 2015)

LightSward said:


> The 72 inch searchlight is incredible, but storage was a problem so I had to partially disassemble it to make room in my shop. I'm currently fitting the 50 inch Monster Searchlight with the 4,000 watt HMI light source. This design is based largely on the 60 inch WWII carbon arc searchlights. It has an incredible focal arrangement so the beam is well cilluminated and should go quite the distance. Just about ready for it's first test run.



I'll be waiting to see it.  A 50" searchlight should be able to focus the light very well, even with an HMI bulb. If I remember correctly, you fired up the 36" on Halloween one year and that got quite a bit of attention lol. I though of doing something similar with a 575W HMI, but I think that would probably get some unwanted attention from the police, as least where I live


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## LightSward (Sep 23, 2015)

kuna said:


> I'll be waiting to see it.  A 50" searchlight should be able to focus the light very well, even with an HMI bulb. If I remember correctly, you fired up the 36" on Halloween one year and that got quite a bit of attention lol. I though of doing something similar with a 575W HMI, but I think that would probably get some unwanted attention from the police, as least where I live



Will be good to see your light work. Do you live in a big city, near a military base or airport. I usually call air traffic control or other relevant FAA knowledge input point to inform them and clear my bright searchlight activities. They really aren't too concerned about searchlights, mostly lasers of any brightness.

I'm hoping this year to fire up the 50 inch Monster on Halloween. Along with typical life size skeleton, 2 foot long Tesla coil Sparks and the searchlight itself on the 2nd floor deck with power cable running down the steps to the ballast in the garage...should be fun.


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## kuna (Oct 6, 2015)

LightSward said:


> Will be good to see your light work. Do you live in a big city, near a military base or airport. I usually call air traffic control or other relevant FAA knowledge input point to inform them and clear my bright searchlight activities. They really aren't too concerned about searchlights, mostly lasers of any brightness.
> 
> I'm hoping this year to fire up the 50 inch Monster on Halloween. Along with typical life size skeleton, 2 foot long Tesla coil Sparks and the searchlight itself on the 2nd floor deck with power cable running down the steps to the ballast in the garage...should be fun.



Yeah I'm in a pretty urban area and about 10 miles from an airport. Definitely not the ideal location. I hope you get some pics and I know you'll have the most trick-or-treaters of any other house in the neighborhood guaranteed 
A 200 Mcd spotlight beam is the best decoration for any holiday


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## LightSward (Oct 6, 2015)

kuna said:


> Yeah I'm in a pretty urban area and about 10 miles from an airport. Definitely not the ideal location. I hope you get some pics and I know you'll have the most trick-or-treaters of any other house in the neighborhood guaranteed
> A 200 Mcd spotlight beam is the best decoration for any holiday



My tribute and a temporary substitute for the 60 inch WWII carbon arc searchlight, for anyone with limited space for storage, (light as seen can hang in closet).
This is an excellent design after many experiments. Someday if I have the room, I'd like to get a GE or Sperry, but for now this will work.:

Excited Law enforcement officers informed me they could see it many miles out on their patrol and just had to come by and see it, since they knew no businesses are out this far.

*Big learning experience. I built this 50 inch Monster reflector six years ago and sort of didn't do much because it needed a very bright bulb to do it justice. Dimmer bulbs just barely made abeam. This thing took the light a and shot it into the night sky. For ease of transport, storage with ease of extraction, I have decided to make this my big light for now. The 72 inch is so big, I had to partially disassemble it just to store the pieces. For now the 50 inch MONSTER will be the big dominant light until I get a shop where I won't drive my neighbors crazy. Have to decommission things a little until I can get into a production facility.

This thing is "AWESOME" Had kind of shelved this light in favor of more efficient reflector designs. This set up allows for less light to be collected from bulb, but with a much longer focal length, the light travels further in a more parallel beam configuration. Beam had the effect of looking somewhat like a laser and was hard to tell from which direction it was coming from when beam aimed near horizon.

50 inch Searchlight MONSTER was shelved for a few years while I was waiting to secure a 4,000 watt HMI 385,000 lumen light source. It is a good substitute for the 60 inch WWII searchlights that need much loving care to keep going. This 50 inch MONSTER will help keep the big light legacy going well into the 21st century and beyond. The beautiful beam is a nice painting to a glorious night sky. Photo from a yard or two away.*







Photo taken behind MONSTER showing the beam traveling several miles.

Photo taken from a block away
 





Photos taken a few blocks away.









*Photo from a block away. Beam paints a nice color in the night sky. Turquoise blue color looks nice.

*







Photos taken around and from a few hundred feet distance.





*Photo from a block away. Walking way from searchlight, the beam appears to follow. Aimed near the horizon, people couldn't tell which direction it was coming from...nice narrow beam compared to my other searchlights.
*
 





*The beautiful beam is a nice painting to a glorious night sky. Photo from directly beneath the beam, next to searchlight.
*
 





* Photo from near mail boxes, block away...300 feet...
*
 




Some good views from a block away...several hundred feet. Couldn't go any where with the crowds coming to see. Police almost said they'd stay and watch while I drove around to take photos.







Some of these composites were hard to align with the camera tripod. Software to straighten the photos was unavailable.








*Photo from a block away.
*

 





*Photo from a block away.*







*Photo from a block away.
*Photos showing beam traveling overhead. Laser like look, hard to tell direction beam came from when aimed near horizon.


*Photo from a block away. Beam paints a nice color in the night sky. Turquoise blue color looks nice.*
*Photo from behind searchlight.
*I'll get back to posting on this shortly.


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## lucca brassi (Oct 7, 2015)

IMO : you have far too much side spill from main reflector - everything around is irradiated and light looses are astronomic ; consequently, the efficiency drops significantly


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## LightSward (Oct 7, 2015)

lucca brassi said:


> IMO : you have far too much side spill from main reflector - everything around is irradiated and light looses are astronomic ; consequently, the efficiency drops significantly



It just looks like a lot of spill light on camera. It's actually not very bright at all. All the light the reflectors can possibly take geometrically or any other way is being reflected away and into the beam. It's actually pretty dark around the searchlight. The light losses are the same for any other light using this arrangement. If you look at a Carbon Arc 60" searchlight, one can see that a significant amount of light is just being bounced around on the barrel and never goes into the beam, but the military GE and Sperry engineers calculated that amount of light loss to be acceptable for how much the reflected light does do it's job well.

My more efficient reflectors that theoretically collect nearly 100 percent of the light, (never a reality), also produce some spill light, similar to the less efficient 200 year design this great light uses, yet because of the shorter focal length, the beam spreads out faster and the result is less light traveling far distances, compared to the less efficient 60" carbon arc design which produces a better beam, the design I used building this magnificent searchlight. The spill light produced does come in handy for alerting motorist they have found the source of the Great Light in the sky..

I figure I'm grabbing anywhere from 40% to 65% of the light, as the split back reflector can only get sop much light bounced back through the arc chamber and two other layers of glass before reaching the main reflector....45% at best, unless split reflector really does a good job then maybe 55-65% of the light is placed into the beam. The beam produced by this light really does act much like the 60" carbon arc lights I've always wanted to imitate. My goal has been achieved. 

Thanks for reading up on this wonderful light.


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## kuna (Oct 9, 2015)

Those composite beamshots are amazing. The amount of attention that light gets must be crazy haha. I can't tell how large your neighborhood is, but if you were to use that light in a somewhat crowded neighborhood such as mine on Halloween the attention might be a little too much  Record number of trick-or-treaters I think lol. I hope you fire up the 50" on Halloween, at least for a short time before your neighborhood is overrun with trick-or-treaters ;D

@ lucca The spill really isn't a problem and all large searchlights have a significant amount of light that doesn't make it into the main beam. I don't think the spill is a problem in this case unless of course you were trying to make the surroundings darker. A deeper reflector would cut down on spill but that's not always feasible when you have such a large diameter searchlight. The WW2 searchlights have a pretty "flat" reflector that doesn't collect a lot of the light, whereas the newer smaller skytracker type lights collect a bit more.


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## LightSward (Oct 22, 2015)

kuna said:


> Those composite beamshots are amazing. The amount of attention that light gets must be crazy haha. I can't tell how large your neighborhood is, but if you were to use that light in a somewhat crowded neighborhood such as mine on Halloween the attention might be a little too much  Record number of trick-or-treaters I think lol. I hope you fire up the 50" on Halloween, at least for a short time before your neighborhood is overrun with trick-or-treaters ;D
> 
> @ lucca The spill really isn't a problem and all large searchlights have a significant amount of light that doesn't make it into the main beam. I don't think the spill is a problem in this case unless of course you were trying to make the surroundings darker. A deeper reflector would cut down on spill but that's not always feasible when you have such a large diameter searchlight. The WW2 searchlights have a pretty "flat" reflector that doesn't collect a lot of the light, whereas the newer smaller skytracker type lights collect a bit more.



Very true. Soon, I should be able to take the 50 inch Monster towards the center of town and 'try it out', in a business setting and see how the result is...expect it to be good.

Will be using the 50 inch Monster up on the 2nd floor deck and surround it with black theater scrim to reduce any unwanted light and glare. Doing my best to make a positive Halloween experience for as many people as possible. This for now is my main light. Wow, and it took a full multi searchlight building route to figure the best searchlight for me, really depends on the light source and need. For sure the 50 inch Monster Needs the 4,000 watt HMI 385,000 lumen bulb to make "it work", correctly, meaning a tight well defined beam going a good distance, this is the main showcase light for now. The other lights are phenomenal sources of entertainment and lighting as well. See more later.


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## kuna (Oct 31, 2015)

It's almost time to light it up . Good luck and be prepared for quite a few people to show up ;D. It's already almost 8 o'clock where i am and we had a good number of trick-or-treaters show up even without a spotlight. I couldn't imagine how many people would show up if I had a similar light at my location. Would be hectic haha

Edit: just looked outside and saw one of the four-beam units running a ways away. Might go track them down just to see a nice spotlight on Halloween


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## LightSward (Nov 1, 2015)

kuna said:


> It's almost time to light it up . Good luck and be prepared for quite a few people to show up ;D. It's already almost 8 o'clock where i am and we had a good number of trick-or-treaters show up even without a spotlight. I couldn't imagine how many people would show up if I had a similar light at my location. Would be hectic haha
> 
> Edit: just looked outside and saw one of the four-beam units running a ways away. Might go track them down just to see a nice spotlight on Halloween



Yes the light was phenomenal. Never had such a line of vehicles like this before.
Just wanted everyone to know this MONSTER 50 inch searchlight is a winner. So many cars came by and used up much of our trick or treat candy..! Met many people from far away towns and small cities. People from towns twenty miles distance said it was bright where they were located.

One day would like to power all the lights at once, but will take a while to have the resources to power all the lights at once. Would like to have them all on at once, some day. Here is how the 50 inch Monster looked Halloween Night.
Hard to say, I'd like to one day have the means to compare many of my searchlights together. For now I can do a 1,200 watt HMI, NightHawk or 36 inch Gorilla, comparison to the 4,000 HMI 50 inch Monster, when the neighbors won't be bothered. Have to do it when the nights come real early next month.

Just wanted everyone to know this MONSTER 50 inch searchlight is a winner. So many cars came by and used up much of our trick or treat candy..! Met many people from far away towns and small cities. People from towns twenty miles distance said it was bright where they were located.

Here are some quick photos, (better ones to be transferred soon), of the awesome Halloween night 50 inch MONSTER searchlight Trick or Treaters flood and hundreds of vehicles on our private street to see what the "Big Light", was all about.. Awesome. Met many great people.







*Another shot taken from a camera hard to transfer photos from. Looks great, will get it in better quality soon.
*


First photo of the night my cell phone camera could actually take.
*At sunset I turned the searchlight on and found it was already dark enough to be seen.


















Searchlight is bright enough to be seen at sunset.





*
* Halloween begins with this brilliant beam that could be seen twenty miles in distant small towns.*




*My 385,000 lumen Four thousand watt, HMI high efficiency, medium arc, 50 inch diameter MONSTER searchlight drew in Hundreds and hundreds of vehicles, multiple dozens of "Trick or Treaters", more than all other years here combined. One photo is from cell phone and one with a rainbow vein, like a rainbow caught in the light beam.
(You can see the high tech light bulb cooling down next to the air cooled 'split half reflector', which redirects otherwise wasted back light, back through the arc chamber, and onto the main reflector.)
*




Beam looked thinner to the eye, but cloud nicely lit.


*Cool photo showing beam splitting raindrops up into colors like a rainbow.*




While the rain was falling heavily, rainbow patterns were visible at various parts of the light beam. Looked real neat.


*4,000 watt, 385,000 lumen HMI High Tech bulb cooling down.*




The split reflector cooling system has reduced the tarnishing effects of the intense heat assaulting the back split reflector.

*
Beam was bright enough for the my cell phone to capture the beam in rain*.





Very impressive. The beam could be seen for many, many miles. People from many of the small and large towns and small cities scattered in the area, came for some candy and to see a searchlight, many had never seen one in person before. The look on many people's faces was like they had just seen God, or were otherwise spiritually lifted. 



Car headlights compete with the much brighter searchlight beam 1:200 ratio in brightness.






Beam isn't totally culminated, but it looks like a laser when underneath it in another neighborhood...I'm told.


Way worth the effort. Now we get many Trick or Treaters when in the entire history of our small part of town, we had almost no people come by on Halloween...ever. I'm stoked....don't have to eat so much left over candy now....HA.

Will have to do this again. Originally I was going to make this the last appearance of the light, but due to high public approval, I may do it again, next year..!







When resources allow, the World's Biggest Searchlight will be "resurrected". For now the 60 inch WWII wann-a-BE Monster 50 inch searchlight will be my Big Light for now. A true WWII searchlight will blow mine away, but it'll be interesting to see how the two would compare. Maybe at Flash-a-holic event to be scheduled soon...I hope..!


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