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One Million Lumen

kdxn

kdxn

New member
Maybe not for cave photography unless you want to try and capture a rope or anchor break on a test rig to aid failure analysis.

Given that somone has created a high power LED flash unit.
Can the caving community create an open source LED flash more suited for cave photography and perhaps with a built-in wireless trigger ?
Or are the high power LED's always on good enough ? 
 
Mr Mike

Mr Mike

Active member
I've played around with doing a LED flash gun using a 100W 9000lm COB LED v Sunpac MX130 Flashgun. The LED was bright and produced a good result, but still wasn't as bright as the flashgun.

In terms of practicality in doing one yourself, there are 2 approaches as you need a you need a much higher voltage to drive COB LED's, the one I used was a 36V one.

1: Use a battery pack that is 36V, and some control / switch / current limit circuitry to turn on the LED

2: Have a much lower battery voltage and use a boost PSU, to charge a bank of caps up and then switch the caps onto the LED.

I wanted to see how the LED behaved using a cap bank, so used 5 x 4700uF caps in parallel to drive the LED that were charged up from a LAB PSU.

This was all done adhock, just to see what potential results could be, so is not refined in anyway. See photos below:


url]
http://www.aditnow.co.uk/photo/Personal-Album-125-Image-97880/
http://www.aditnow.co.uk/photo/Personal-Album-125-Image-97879/

url]

 
Mr Mike

Mr Mike

Active member
BTW, can someone tell me how to show the image in the thread: I tried using  the "Insert Image" button and then putting the link in between them, but no joy...
 
bograt

bograt

Active member
Thanks for that TBE, so, Mr Mike, that was taken by capacitor discharge through a LED? would like to see an underground example. Could be a marketable item (y)
 
O

Olaf

New member
I've built some LED flashguns for cave use with integrated remote trigger. It's certainly no magic.

I took a JeeNode, which is basically an Arduino with an integrated little radio transmitter. With a few extra components wired up as inputs, it's fairly easy to program the microcontroller to do all sorts of fancy stuff, like monitor the battery voltage, LED temperature etc and adjust the brightness of the flash using PWM signals.

Next to the JeeNode I wired up, in two different units, either 4 Buck step down converters that each drive 3 Cree XM-L's at 3A in series, or two Boost step up converters that each drive 7 Cree XM-L's at about 3A in series. At full power they give something like 10.000-15.000lm and I can leave them on for half a second or even a couple of seconds. I can control the brightness in 256 steps down to a very dim light, that can probably run for a couple of hours without breaking anything.

They are all powered off 13.2V LiFePo battery packs and wrapped in transparent, waterproof Peli cases. The control unit that plugs into the camera hot shoe even has a fancy display and buttons and stuff, and simply runs of 2 AA batteries.

Altogether they work fairly well for photography, although one of them is currently sitting on my pile of electronics that need repairing. The components are not cheap, though, and sum up to about 150-200 GBP per slave unit. Nice hobbyist project, but probably you are better off buying bog-standard off-the-shelf flashguns cheaply on ebay.


Back to the original topic, I was indeed wondering what this 1.000.000 lumen thing does and couldn't find what sort of extra tricks they are doing. Are they just driving the LED's at some insane current for a very short time and hope that they'll survive it?
 
paul

paul

Moderator
Mr Mike said:
BTW, can someone tell me how to show the image in the thread: I tried using  the "Insert Image" button and then putting the link in between them, but no joy...
Click to expand...

I tried to fix the problem by adding '[ img ]' tags, but you have posted URLs to pages, not the image files themselves. Now I noticed that Bottlebank has fixed it anyway!
 
Bottlebank

Bottlebank

New member
Mr Mike said:
BTW, can someone tell me how to show the image in the thread: I tried using  the "Insert Image" button and then putting the link in between them, but no joy...
Click to expand...

I didn't fix it!

I think what you need to do is right click on the image to get the actual URL of it and insert this between the image tabs (copy image URL in Chrome, click on properties in Explorer and copy the URL)

e.g.  ...img]http://earbypotholeclub.co.uk/wp-content/uploads/2013/12/Last-of-the-Summer-Wine-Dig-4th-August-2013-023-1024x768.jpg[/img...

Last-of-the-Summer-Wine-Dig-4th-August-2013-023-1024x768.jpg




 
B

blackholesun

New member
Right, let's have a go:

Take:
9 COB LEDs, normally driven at 34V and 1500mA, for 5000lm.

Drive them:
20 times harder

Giving:
9 * 5000 * 20 = 900,000 lm

Assuming:
a) Output stays linear with current
b) COB LEDs behave like Cree XML's, described here:
http://electronicdesign.com/power/generate-realistic-models-led-current-versus-voltage
giving a 20 fold increase in current for a 80% increase in voltage from normal operating conditions
c) LEDs behave like resistors to capacitors for a given voltage drop and current
d) Your RC time constant is 500ns

Then:
Overdriven current = 1500mA * 20 = 30,000mA
Overdriven voltage = 34 * 1.8 = 61.3V
Effective resistance of 9 LEDs in parallel = 1 / (9 / (61.3 / 30)) = 0.23 Ohms
Necessary capacitance = 500ns / 0.23 Ohms =  2.2 micro Farads

Energy in such a capacitor = 0.5 * 2.2E-6 * 61.3^2 = 0.004J

As a check:
Peak lumens = 900,000
Average lumens (Roughly) = 450,000
Average power = 4,500
Total energy = 0.002J

So I've lost a factor of two somewhere in the assumptions (or quite possibly the calculations), which isn't surprising. So, it looks on paper at least, that a few batteries, a transformer, a 100V 2uF capacitor, and 9 50W COB LEDs should be able to get you something close to this.
 
B

blackholesun

New member
For some much simpler calculations

1,000,000 lumens for 0.000,000,500 seconds gives 0.5 lumen seconds.

This means it will expose an image the same way that a Duo would for an exposure time of 1/120 of a second.

Thus it is really fast and really far too dim for caving.

However perhaps the concept could be appropriated to give some brighter caving LED flashes.
 
kdxn

kdxn

New member
Some interesting ideas.

Something to aim for is a reusable digital product that replaces the equivalent of the Meggaflash PF330 bulb. The PF330 generates 140,000 lumen seconds or an average of 56,000 lumen over the 2.5second illumination period.

The 100W COB LED provides 14,000lumen so (in theory) that would need to be on for a 10second bulb camera shot although need to experiment with reflectors to compare the lumen spread with the PF330/reflector combination.

An AA battery powered 100W COB LED flash unit with remote trigger might be useful.
 
Mr Mike

Mr Mike

Active member
For me the whole point at looking at LED flashes is to make it instant and no charge time, so ideally the LEDs are driven directly from a battery pack (with current limiting) and simply switched in and out for the time required. Also, there is no point in the LED flash ending up bigger than a normal flash, which might be the case if using multiple dies or COBs. Some of the top Cree COB LEDs output up to 17,000lm. So maybe 1 or 2 of these over driven for short periods might work well in terms of getting the light output to required levels.

As already mentioned, doing it via LEDs is a curio project and can easily rack up in to the ?100's. Far simpler and cheaper to buy flashguns.... at the moment that is.

BTW, blackholesun, 2.2uF is a time constant only, and nothing to do with power delivery to the LED, 2.2uF won't do anything for your LED in terms of powering it. I needed 23,500uF to get the light output in the photo.

For everyone's information that is the desk/office side of my lab, cluttered with boxes of parts and other electronics stuff, oh and a bit of mine exploring gear - red bag.... before we have more concerns of burglars and the like  ;)
 
Mr Mike

Mr Mike

Active member
Cree have an application data sheet for over driving LEDs, they have done experiments for over driving by 2-3 times rated current with PWM topologies. They do stress that you reach a point where the power consumption has got so high that the LEDs really loose their output power. For those that did not know the relationship between output lumens and input current is exponential.

I think that for experiments with really over driving LEDs, Chinese cheapies from Ebay and the like should be used for testing, as they are a fraction of the cost and no big deal if blown. You can easily get 100W ones that give out 10000lm. Reserve the Crees for the real thing.
 
TheBitterEnd

TheBitterEnd

Well-known member
Olaf said:
I've built some LED flashguns for cave use with integrated remote trigger. It's certainly no magic.

I took a JeeNode, which is basically an Arduino with an integrated little radio transmitter. With a few extra components wired up as inputs, it's fairly easy to program the microcontroller to do all sorts of fancy stuff, like monitor the battery voltage, LED temperature etc and adjust the brightness of the flash using PWM signals.

Next to the JeeNode I wired up, in two different units, either 4 Buck step down converters that each drive 3 Cree XM-L's at 3A in series, or two Boost step up converters that each drive 7 Cree XM-L's at about 3A in series. At full power they give something like 10.000-15.000lm and I can leave them on for half a second or even a couple of seconds. I can control the brightness in 256 steps down to a very dim light, that can probably run for a couple of hours without breaking anything.

They are all powered off 13.2V LiFePo battery packs and wrapped in transparent, waterproof Peli cases. The control unit that plugs into the camera hot shoe even has a fancy display and buttons and stuff, and simply runs of 2 AA batteries.

Altogether they work fairly well for photography, although one of them is currently sitting on my pile of electronics that need repairing. The components are not cheap, though, and sum up to about 150-200 GBP per slave unit. Nice hobbyist project, but probably you are better off buying bog-standard off-the-shelf flashguns cheaply on ebay.


Back to the original topic, I was indeed wondering what this 1.000.000 lumen thing does and couldn't find what sort of extra tricks they are doing. Are they just driving the LED's at some insane current for a very short time and hope that they'll survive it?
Click to expand...


Sounds interesting, have you written the design up anywhere - CREG Journal for example which is often looking for decent articles.
 
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