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Registered Member #10
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).
Registered Member #10
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.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
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.
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.
Registered Member #10
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.
... not Russel! Registered Member #1
Joined: Thu Jan 26 2006, 12:18AM
Location: Tempe, Arizona
Posts: 1052
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.
Registered Member #10
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.
Registered Member #10
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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World's brightest flashlight
