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)
Grin , I know OZ is a vast country so I don’t want to sound ignorant - but I always thought there were a lot of helicopters there (sorry, tv programs here always showing sheep rounded up by heli lol)
It would be AMAZING to see the beam from above! - know anyone with a heli - OR a drone? 
Thanks for the feedback. Even constructive criticism welcome.
I am waiting for a telescope so I can see the beam, I just hope it has enough range.
I have a decent light meter but I have not been able to get consistent results so I dont like to post the readings. The other thing is this is not really a light yet and the light source is hard to focus properly because the mount isnt solid.
Goose seeing the beam from a plane would be something else there is an airport about 6km from me so I have been thinking about how to do it. I have a gsm module I can control from my phone. the lights just need a bit more work.
The next challange is going to be difficult
Parachute jump whilst filming…… and get lit up! wow! NOW THAT would be a video! maybe make you pootube legend! 
Maybe rope in that Felix Baumgartner Austrian daredevil! (just kidding lol) or put a balloon on a tether with a go pro?
Haha I cant do night jumps yet. They have an airshow here and I would be good to light some tiger moths or p51 even yakolevs over the local town.
Doh! I forgot about the night bit, just a tiny detail lol! :person_facepalming:
There are a few ideas I have for some cool beam shots. The cliffs I posted photos previously being one idea.
I have had more than a few goes at trying to get I think it is a lantern style of light right. Anyway this is the latest attempt.
The lens and reflector somehow got more than usual.
LED is a cree cmt-1945 5000k, driver is a taskled HBflex, it doesnt have a battery yet but is setup for external power from an 18v makita battery. the back/battery pack and base are still to be designed and built.
Your work is pure pawn grin.
i like how you tapered the body section with the heat sink fins, that adds some style points to the looks.
Plus all the large diameter inside fine threads that you’ve been able to cut.
cheers to ya.
[edit]
Nice build… now that’s a big boy flashlight hahaha
A while ago I actually purchased one of these
https://www.amazon.ca/SMALLRIG-Handle-1447-Rubber-Black/dp/B00MP2YEMG/ref=sr_1_46?dchild=1&keywords=grip+smallrig&qid=1595656949&sr=8-46
And a 25mm led ring push button switch fits perfectly in the handle, since you can easily remove the black end cap
Makes a really nice and comfortable handle 
I have some similar to those handles although you cant get a switch them. Contacts in the handle base like a camera flash would be good so the handle could be removed easily. Then remote switch magnetic base so I can put it on the roof of my car for out bush.
Does anyone recognise what the front is from?
I was using alternate spelling so not to attract the ire of sb.
Ah, yes, sb doesn't like the word for "adult entertainment" on BLF because this site might be classified as an "adult website."
Very cool! 
I'm wondering though how you got such a high lux number with the calculator.
A 900mm reflector has a surface area of around 636,173mm2 minus the dead part in the middle where the LED heatsink is. You need to multiply this with the reflection losses. Since you are using a very old reflector I would go with 70% here. After this you just need to multiply this with the luminance of the LED.
COB LEDs have a rather low luminance. Your COB, the Cree CMT2890, has an LES of 22mm (diameter of light emitting surface). This allows for a rough calculation of the luminance by dividing the lumens by the surface_area x pi. At 15,000 lumens your LED should have an average luminance of around 12.6cd/mm2 (COB LEDs have many small dies with dead areas in between them so the real area is smaller and the actual luminance a bit higher). Multiplied with the area of the reflector I got around 8 Million Candela. This shows that you are leaving quite a bit of performance on the table. A Luminus SBT90.2 should easily reach 200cd/mm2 while giving you 1/3 of the lumens. Also, there a much brighter COB LEDs on the market if lumens are more important to you.