Thats crazy grin. 
That is the envy of us all 
I love watching your builds. Looking like a WW2 search light 
Thanks,
sometimes I do things for no real project in mind but a 4s1p 26650 battery carrier would be handy wouldnt it? You never know when you might need one and it does fit into 3inch ali tube.
That searchlight that you can see 3km away is a budget light in that configuration.
Mirror $250
A rallyexpress “200W” HID headlamp those crazy ones.$80
4x38120 3.2v lithium batteries about $100
Frame screws cable and other stuff say $150
I made the light mount
So AU$580 or US$400
I found that there was a military agreement to have a common standard around WW2 and the metric system has been around a long time. The numbers on the mirrors correspond to metric, 90cm aperture, 408mm focal length. So with that bit of information I have narrowed down the light they were used in.
I couldnt find any detail as to how they were originally mounted but now it appears to to be fixed and the light is on a pedestal and the arc is moved.
The more I find out about them the more I am drawn to building them with the original in mind. The rails on the side look like they would make it simple to balance it.
“Ralphie, you’ll shoot your eye out”
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Wow, that will need a cooling system ! and a generator too.
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900mm mirror with CMT-2890 @ 2.8amp ridge is about 1.6km
Very nice round spot 
Could def use that to spot planes in the sky.
Haha i would like t9 see it from a plane. with your calculator it comes out at 119Mcd. Here is a video taken that night by another forum member.
Is there a maximum distance ‘any’ light can throw, or is it infinite? Or is the maximum throw defined buy brightness/reflector etc?
Just curious I know it’s an odd question. For example, if you had a mirror 3x the size of yours, and the light source was 3x brighter, would it go 3x further?
Mathematically it’s infinite - you can always create a larger mirror. But at some point you’ll arrive with a light that has extremely low intensity at any distance - it just produces a beam that widens very slowly but is extremely large even at the start.
Physically - dunno.
I am not exactly sure but someone did some calculations on here and it was suggested that you need to increase the reflector surface area 4x to double the throw. I have a few big quads in to works one will be 4 GT reflectors with 4 sbt-90.2s once that light is built I will be able to take measurements and compare the numbers, I am hoping to out throw the lemax by 1km. Will be interesting to see what the numbers are.
Another thing I think determines throw and beam size is focal length. Longer focal length will give you smaller beam diameter and more throw than a shorter focal length.
Another thing is light source size.it is very hard to take pics next week or so I will try again.the 2890 has a 22mm light surface and I would estimate the spot size at 1.6km to be around 150m. A 100w HID will give a spot diameter the width of the road about probably 10-15m
Light from stars travels for years II dont really know if there is a limit.
It also depends upon the media and environment, e.g. in vacuum vs in air. For laser distance measurements the barometric pressure, humidity, temperature affect the wavelength.
Interesting. I nearly mentioned stars, but didn’t for fear of looking an idiot lol! And… they don’t have reflectors. That being the case, I can only imagine there is not limit, only to the one ‘viewing it’.
Stars are just pure brightness, and we can see some with our eyes - others we need telescopes for.
In theory, someone could see your light from the furthest depths of the universe, given a big enough telescope…… gets you thinking lol!
Light can travel infinitely, that’s how we can see outer parts of the universe, it’s because light has travelled a few billion years to get here.
So there really is no limit.
The only thing is that on earth there is atmosphere and particles and other stuff that blocks light so the intensity actually begins to decrease at a rate faster than 1/r^2, but yes you can always make a light more powerful and have it go further.
Also yes, if your mirror has 3x the front area and your light source is 3x brighter then you have 9x the candela, which means it will go 3x farther (because sqrt(9) = 3) but slightly less when you take into account the atmospheric losses as I mentioned above.
[quote=grin]
900mm mirror with CMT-2890 @ 2.8amp ridge is about 1.6km
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Wow 1.6km and bright as day.
I’m thinking you may need a camera set up in a telescope to see its full range !
I really like the pic from across town, burning a hole in the sky
Have you considered a lux meter for some measurements?
Thank you :+1: , I kinda knew you’d step in and I know you are very knowledgable about it - I can’t believe I was right though lol! (3x further)