[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
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.
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?
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.
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'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.
I would assume he’s using the 200cd/mm2 from the SBT90.2 otherwise it’s not above 100Mcd.
With 200 it does show ~120Mcd but that’s only with a perfect mirror, so you’re right he should be doing like 70-80% reflectivity to get more accurate numbers.
The variable for that is in the “intensity calculations” folder in the calculator
There is also a glass transmission variable which can be set to 1 since he is not using any front glass for the light.
You are correct I would trust your calculations over mine but when I looked again that number is for the sbt-90. My measurement is usually “it hurts my eyes so it must be bright” and “I pointed it at that house 2km away and they called the police it must throw a fair distance” haha around 3am one morning I lighted up someone sleeping on the job over 2km away.
I am trying different light engines out of curiosity and also to get a feel of what the mirror is capable of. SBT-90.2 is impressive, HID is good fun, CMT puts out a column of light. Looking at original light it was designed to be carried by hand so everything has handles built in, the genset was towed on a truck. By the looks of it the carbon arc assembly sits inside an enclosure inside the drum. Looks like it dropped in and was fastened so it didnt move. In my lights I would like to have it the same but build the cooling system, driver and maybe even a battery into the one module. That way if I was to hire them out depending on the use the light engine can be changed. I want one portable and one mounted on the mini dump truck. How would a plasma cutter or a tig welder go for a light engine? A small bottle of argon would last an hour or 2 to purge the oxygen from the electrodes about the same as carbon rods.
Screen shot from google of the 90cm carbon arc searchlight.