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4hv.org :: Forums :: General Science and Electronics
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World's brightest flashlight

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Tesladownunder
Sun Nov 07 2010, 10:47PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
After a lot of work on the bike I have returned to do some more on the flashlight. I now know how I will attach the barrel to the light source, so can go ahead with the internal frame.

At present only the red, blue, green and one of the 12 white LEDs are in action and no lenses yet. So "only" 400W (instead of 1500W).







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Thomas W
Mon Nov 08 2010, 07:39AM
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location: UK, Dorset, Broadstone
Posts: 1275
Thats big
Realy big
how long does it run and does it need a power lead?
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Tesladownunder
Sat Nov 13 2010, 08:17PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
I now have the flashlight largely completed apart from populating the front array with 11 white LEDs. Total power at present is 400W which is just over 1/4 power.
It is heavy at 45kg and still has 5kg of lenses and fans to go.






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Chris Russell
Sun Nov 14 2010, 09:55AM
... not Russel!

Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1047
Tesladownunder wrote ...

Space = arbitrary 100 miles. Lets look at the reverse. A satellite can easily be seen against a black sky with dark adapted eyes - particularly the Iridium series. These will reflect light from the sun at 200W visible light per m2 from a 1 degree source. The reflecting surface will be say one square m from the satellite. ..... actually I am having trouble getting my head around the concept. Anyone want to have a go with those parameters?


Okay, just for fun, I did the math. Here's what I came up with. This may be a little messy; I'm mostly just copying and pasting from my notes.

I figured the easiest way to answer this question would be to consider how bright various things in space are on earth. This is called apparent visual magnitude. Happily, apparent visual magnitude can be converted to lux, or lumens per square meter, using the following formula:

Apparent magnitude: Negative numbers are brighter. Every five magnitudes is 100 fold increase in luminosity. An apparent magnitude of zero, on earth (ignoring atmosphere), is equal to 2.54e-6 lux.

Therefore, [2.54e-6 lux]/[100^(1/5)]^[Apparent Magnitude] = lux (lumens per square meter). Simpler: lux = 2.54e-6 / 2.512^a

Also works in reverse. a = -[log(50000000 * lux/127)]/log(314/125)

Proof we're not way off: -26.74, Sun's apparent visual magnitude, equals 131,000 lux. Direct sunlight is 26,000-130,000 lux depending on factors like altitude, angle, dust, etc. Looks good, since apparent magnitude is normalized to no atmosphere at all.


So then, my reasoning goes as such:

TDU's flashlight: 84,000 lumens
Half power beam width (2 * theta): 5 degrees (theta = 2.5 degrees)
ISS orbital altitude: 425000m
TDU flashlight half power beam width diameter at 425000m: 2 * tan(theta) * 425000 = 37100m
Total illuminated area (assume circle) = 1.08e9m^2
Total illuminance inside half-power area: (0.5 * 84000 lumens)/1.08e9 m^2 = 3.89-5 lux = -2.96 apparent visual magnitude


So, if TDU were to shine his flashlight at the ISS as it passed overhead at night, observers on the ISS would see a point of light about as bright as Jupiter, at maximum brightness, appears here on Earth. That's pretty impressive, actually, and provided someone on the ISS were looking at the Earth at that moment, it would be very noticeable.

Note that 425km is actually the maximum altitude of the ISS. At its lowest, the altitude is 278km. If we are kinder, and use the median altitude of the ISS (352000m), the numbers are even better: 5.68e-5 lux, and -3.37 apparent visual magnitude. That is noticeably brighter than Jupiter, and approaching the minimum brightness of Venus.

And, just for fun, if TDU were to stand on a mountaintop and shine his flashlight at an observer far below, 10km away, on a clear night: 0.0701 lux, -11.1 apparent visual magnitude. That's brighter than a half-full moon, and given the beam profile, probably bright enough to start triggering alien abduction stories.
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Tesladownunder
Sun Nov 14 2010, 07:13PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
Chris Russell wrote ...

Okay, just for fun, I did the math. .... So, if TDU were to shine his flashlight at the ISS as it passed overhead at night, observers on the ISS would see a point of light about as bright as Jupiter, at maximum brightness, appears here on Earth. That's pretty impressive, actually, and provided someone on the ISS were looking at the Earth at that moment, it would be very noticeable.


That is all fascinating and brighter than thought. I am a bit surprised that any light would be visible over a 37km beam spot. Thanks for that calculation, I am sure I will quote it frequently.

I just received a light meter I bought on eBay, covering 5 decades up to 400kLux. Sunlight reads about 100kLux early in the morning and my previous single white LED is 200kLux at the lens at 10cm. I probably need to work things out a bit further out when the beam is defined at 5 degrees.

I am preparing a big white cloth backdrop (3x4m) to shine the beam against to compare with other light sources such as car headlights that have a different beam dispersion. I have the frame and the wife has done the sewing. Also a good black backdrop for general photos.

One thing that I would like to do is audio modulate the beam and hook a receiving solar panel to a speaker. That would be cool. This can't be done with full modulation with any other light source really. I could communicate with the ISS covertly.

I have only two LED's to go in the array to be fully populated so hopefully more results soon.


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Chris Russell
Mon Nov 15 2010, 08:45AM
... not Russel!

Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1047
Tesladownunder wrote ...

That is all fascinating and brighter than thought. I am a bit surprised that any light would be visible over a 37km beam spot. Thanks for that calculation, I am sure I will quote it frequently.

I just received a light meter I bought on eBay, covering 5 decades up to 400kLux. Sunlight reads about 100kLux early in the morning and my previous single white LED is 200kLux at the lens at 10cm. I probably need to work things out a bit further out when the beam is defined at 5 degrees.



Thanks. I should note that Jupiter is near maximum brightness now (-2.5), and it is fairly impressive to look at, even when it's close to the moon and seen from a light-polluted city like mine. From space, at night, against the backdrop of a relatively dark Earth, I'd imagine the flashlight would be quite hard to miss. Anyone know someone on board the ISS?

Of course, the calculation assumes that power is distributed equally along the entire 5 degrees. Some measurements of the beam at an intermediate distance of some meters could probably help create a more refined calculation.

Full modulation would be amazing. I've seen LEDs and photodetectors communicate over distances of miles just using atmospheric scattering; both were simply pointed straight up rather than at one another. With a good photodetector and lens, and the flashlight aimed at the horizon, I wouldn't be too surprised if communication were possible over 100km+ distances in darker areas.
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Tesladownunder
Tue Nov 16 2010, 02:54PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
The beam is actually a square and you can make out the individual elements and even the bonding wires if the optics are good. With multiple LEDs all at an angle, the net result should be circular and reasonably uniform.

I have now populated the array. It is a real rats nest of point to point cabling for wires carring 100mA up to 60A. Remember each LED is buffered with a 6v 3A auto globe although the only one that lights up here is the Red LED that has to drop much more voltage, hence uses both filaments of a globe plus a resistor. The globes are a non linear resistance that allow current sharing, current limiting under diffferent loads and also are a fuse with less thermal inertia than the LED.

Power here is 11A at 31V = 320W which is around 20% of capacity.







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Adam Munich
Tue Nov 16 2010, 09:24PM
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2236
Did you find any more hidden numbers in the LEDs?
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Tesladownunder
Mon Nov 22 2010, 12:39AM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
Grenadier wrote ...
Did you find any more hidden numbers in the LEDs?
That was just a quirk of the threshhold and active surface configuration. No more hidden messages.

And is it bright? You bet. Vastly brighter than anything I have access to. The beam is a flat uniform and surprisingly well demarcated disc of light of approximately 5 degrees. There is a lot of light spill outside or a degree or two away from the focal beam giving a surrounding umbra.

On full power (front array only for the Flashlight) voltage is 36.8v and 43.7A ie 1600W in of which about 1300W gets to the LEDs and the rest goes to ballast lamps and fans. Add another 300W for the bike with the rear lights although the voltage drop will reduce that but looking at about 1800W.

Here are some lenses and the completion on the front array. And a low power shot with blue and red LEDs on.
Also shows the trolley setup as I don't like lugging 50+kg more than a few steps. But it is still portable... I have made the trolley adjustable and able to be placed at any angle from vertical to horizontal.





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Chris Russell
Mon Nov 22 2010, 01:40AM
... not Russel!

Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1047
Time to get in touch with someone on the ISS!

Excellent work, can't wait to see more.
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klugesmith
Mon Nov 22 2010, 02:33AM
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1456
TDU: with your luxmeter you can determine the candlepower.
Simply measure the lux at distance of say 100 meters (so you're properly in the far field)
and multiply by 100^2.

Re. ISS visibility: I figured numbers similar to Chris's.
I honestly don't want to rain on anyone's parade, but the candlepower aren't that spectacular
because, as TDU says, the LEDs are a diffuse source & hard to focus into a narrow beam.

Half of 84000 lm in a 5-degree-wide beam (0.006 steradians) is about 7 million candlepower.
Companies like to advertise handheld spotlights with higher cd ratings (probably a stretch)
that put out fewer lumens, but tune the optics to make the narrowest possible spot.
Ordinary green laser pointers have comparable candlepower (single digit lumens in sub-milliradian beam).
Trailer-mounted searchlights are in a different class -- you could rent an honest 120 Mcd unit to advertise your event, or summon Batman. Real IMAX projectors (not the lame digital IMAX in shopping mall cineplexes) have a 600000 lumen lamp with source area less than 1 cm^2.


The instant on/off modulation capability makes TDU's LED flashlight uniquely good for, say, signaling to an observer at (or from) a distant mountain. Maybe even in the daytime -- you can aim close enough without needing to see the beam. In the great war, on/off modulation was done with mechanical shutters like Venetian blinds. Please keep us on the news list!

-Rich

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Tesladownunder
Mon Dec 06 2010, 01:19PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
Chris Russell wrote ...

Time to get in touch with someone on the ISS!

I hope to contact Andy Thomas (Aussie NASA astronaut) sometime once I have a solid proposal for the ISS team to look out from their new cupola.
I would need to servo my flashlight with a small telescope that can be set at least every 5-10 seconds to allow coverage of the invisible ISS position in the 5 degree beam.

Klugesmith wrote ...

TDU: with your luxmeter you can determine the candlepower.
Simply measure the lux at distance of say 100 meters (so you're properly in the far field)
and multiply by 100^2.

Re. ISS visibility: I figured numbers similar to Chris's.
I honestly don't want to rain on anyone's parade, but the candlepower aren't that spectacular
because, as TDU says, the LEDs are a diffuse source & hard to focus into a narrow beam.

Half of 84000 lm in a 5-degree-wide beam (0.006 steradians) is about 7 million candlepower.
The instant on/off modulation capability makes TDU's LED flashlight uniquely good for, say, signaling to an observer at (or from) a distant mountain. ....

I need to get the data from farfield. I have some nearfield readings but they are not really meaningful. At each lens the reading is about 200klx (sunlight 130klx).
Testing a single focussed 100W LED at 25m the meter gave 36 lux. So by your formula candle power is 36*25*25=22,500. Multiplying this by the 15 LEDs gives 337,500. Of course, I need to measure the array directly, but it is a long way from 7 million which I would associate perhaps with a highly focussed HID light. I need to get my head around all these photonic terms.

I have done the video shoot with interviews, overlays and details of the bike, flashlight and Xmas tree with Santa riding the bike. It will be the colors rather than the maximum power that will be the best TV feature of this bike.
Still need to get a good "money shot" still which is tricky with 4 light sources to get right.
Also need to finish off some video of comparative flashlight shots then it's finished.

Here are some data though. Switch on current for one LED is about 7A decaying over 200ms to 3.4A as the ballast filament heats up. Switch on light output (measured by silicon cell) is only up 5% however, so it seems that they are being driven reasonably fully at least individually with full battery charge. Actually I have just realised that was for switching the full array on so the data are not really comparable. I need to recheck this properly.





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Chris Russell
Tue Dec 07 2010, 09:40AM
... not Russel!

Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1047
Tesladownunder wrote ...

I hope to contact Andy Roberts (Aussie NASA astronaut) sometime once I have a solid proposal for the ISS team to look out from their new cupola.
I would need to servo my flashlight with a small telescope that can be set at least every 5-10 seconds to allow coverage of the invisible ISS position in the 5 degree beam.


That would be a really awesome experiment. Many of the astronauts on board will be familiar with Morse code. Perhaps you could relay a brief message to the station using either on/off modulation, or visual FSK (only red, blue, or green on = off, everything on = on). Fortunately, with a five degree wide beam, aiming doesn't need to be too precise.

I don't know if a telescope would be necessary. Amateur radio operators make use of keplerian elements to aim their antennas at orbiting satellites (and the ISS) during passes, which works well even for antennas with a beamwidth similar to your flashlight. A properly calibrated gimbal with markers for elevation and azimuth could allow the flashlight to be rotated through the path of the pass manually. Of course, there are two-axis rotors, but getting one to work with your flashlight might be... problematic.
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Tesladownunder
Sat Dec 11 2010, 05:13AM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
This is my first distance shot. 2.5km along the straight stretch of Lillydale Rd out of Bunbury.
Photo 1 shows the 1/4 moon for brightness reference and a car heading down that stretch about 100m away. My son's car taillights are in the foreground.
Photo 2 shows the Flashlight firing the white LED's 1200W from 2.5km. The moon has moved to be a bit obscured by trees (long wait for a car free period).
Photo 1 shows the green light alone to confirm the source.

I believe Chris' calculations about 1/2 moon brightness at 10km now. It just didn't seem intuitively right before.

Now I want to try Bunbury to Busselton (up to 45k) but I will need to get a vantage point either end to allow it to get over earth curvature (3.6m drop). This pic of the comet shows a 35 km view to Busselton (horizon lights on left) to Cape Naturaliste lighthouse on right.







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Tesladownunder
Mon Jan 10 2011, 06:33PM
Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424
I have received a response from NASA who have forwarded my proposal to the operations team. It's just a foot in the door but is a first step. Fingers crossed from here.

My proposal has been fine tuned significantly since I last wrote and is in detail here on my site.

In essence one plan is to go to a place where there is a 90 degree pass over by the ISS at night. Set up the static flashlight vertically. Brightness based on measured lux values is about that of Canopus, (Apparent magnitude -0.72). Flash a Morse coded message in the 2.5 second flyover with the ISS using their 400mm Nikon D3 with open shutter and not tracked. The Morse code can be read out on the film which provides proof of sighting for Guinness.
There is 8 seconds of visual view time on the ISS with a static flashlight.
Plan B is to have the flashlight track the ISS to get longer visual view times (perhaps 1 minute).

My proposal was:
Subject: Potential publicity photo for ISS. Request night photos of Western AustraliaI have a proposal that may be easy for the ISS to perform and give a nice TV news segment. Also perhaps world firsts such as seeing a flashlight from space or reading Morse code from space.
It is a positive article easily understood by the public and takes only minutes of ISS astronaut time.
I have made the World's most powerful flashlight at around 84,000 lumens nominal. (Guinness Record applied for)
With a 10 degree beam (around 32,000 lumens) this will be visible at ISS altitude as apparent magnitude –0.7 at 230 miles altitude which is the brightness of Canopus, the second brightest star.
The thing about this light is that it is bright and being LED rather than incandescent or discharge can be modulated into a morse code, or even an audio signal.
Accordingly a night time ISS pass in astronaut waking hours over South Western Australia in the next 3 summer months (generally cloudless and low population density) would see this.
A long camera exposure (NO tracking required) would therefore present a string of "dots and dashes" on the picture whereas all other lights will be streaks. It should be a striking picture from which Morse code could be read.
I would not need to track the ISS once set up for a single photo still, but would with an accuracy of 5 degrees if it was to be viewed directly by an astronaut as well (preferable).
If this proposal is of interest I can present more solid data, mechanical tracking information, Guinness information and plans for optimal siting for dates and times. In particular aiming for a near 90 degree elevation.
I am an Australian experimenter with a high media profile (eg on Discovery Channel 5 times) and have the resources to make this a success from my end.
My relevant web page and proposal is here:

This shows the relative positions of the ISS (using the Nikon D3 400mm lens) and the Flashlight.




This shows a simulated view from the ISS camera with open shutter for 2.5 seconds showing my flashlight
modulated light amongst the other town/city lights. This will be morse coded to give a brief message.




This is the flashlight viewed from 9km.

The ISS view at 230 miles will be less by a factor of 1700 but still very visible at night to the naked eye.





NASA's response:Thank you for your message. I have forwarded on your request to our operations team for review. Acquisition of specific target imagery from the ISS is dependent on several factors including the crew task schedule, orbital position of the spacecraft, and environmental factors (cloud cover in this case).

The crew does sometimes take imagery of areas outside their standing science targets, and I recommend that you periodically check our online database for night time imagery of the western Australia coastline to see if the Bunbury region has been acquired. You may use our technical search tools at for this purpose, I would recommend doing a combined Geographic Region and Features search (use the keyword “night” – no quotes required).

We also have an Uncataloged image search tool at - crew discretionary images as described above are typically not high priority for cataloging, so you are most likely to find new imagery using this tool.


Thank you for your interest in astronaut photography of Earth!
Earthweb
The Gateway to Astronaut Photography of Earth
NASA Johnson Space Center


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Chris Russell
Mon Jan 10 2011, 08:19PM
... not Russel!

Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1047
Looks like kind of a canned response to a "take a picture of my house please" type of request, but it's good to have a foot in the door. Hopefully the next person up the chain will take a closer look at your proposal.

The 2.5km picture is amazing.
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