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LED Flash
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Mr Mike
Posted 3/8/2012 11:38 (#97867)
Subject: LED Flash


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Location: Bury - In The Laboratory		Thought I would mention that I had a little play with making a solid state LED flash. Food for thought results.

I got a 100W LED from Ebay, approx 9000lm @ 34Vish 3.2A, and built a little test circuit on the bench. Basically charging up a bank of caps (40000uF to 35V) and discharging via the LED and comparing it to a old small Sunpak MX 130 Flash gun.

The flash gun won, on the light output stakes, but a few notes:

The ting tong LED, states 9000lm @ 100W, I do think this is optimistic, the Chinese are way behind on such outputs, a western made power LED at 100W would be giving out around 12000lm, which could maybe make the light output equal judging by the photos.

It is still easier to buy a 2nd hand flashgun and use that, compactness for starters.

It would be a different matter if you had a compact portable 35V 3.2A supply, but that is not going to happen any time soon, so I built a single cell Li-Ion PSU that gave out 35V at low current to charge the capacitor bank, took about 20s, this could be easily improved, but the cap bank is still big!

The exposure was 2.5s, F/2.2, ISO100, with just firing the flash and LED.




(LED Flash S.JPG)



(MX130 Flash S.JPG)



Attachments
----------------
Attachments LED Flash S.JPG (69KB - 72 downloads)
Attachments MX130 Flash S.JPG (53KB - 71 downloads)
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royfellows
Posted 3/8/2012 14:50 (#97868 - in reply to #97867)
Subject: RE: LED Flash



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Just looked at the pics Mike.

Did the burglars take much?
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Mr Mike
Posted 3/8/2012 15:16 (#97869 - in reply to #97868)
Subject: RE: LED Flash


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Location: Bury - In The Laboratory
royfellows - 3/8/2012 14:50

Just looked at the pics Mike.

Did the burglars take much?


Yeah yeah, thats one end of the lab, been busy, too busy to tidy, drives the wife crazy, "how can you work like that !"
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moonwalker
Posted 3/8/2012 19:03 (#97871 - in reply to #97867)
Subject: Re: LED Flash


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Location: Near Edinburgh, Scotland.		Wouldn't the results of this test be skewed in favour of the flashgun if it has a longer decay flash than the cct with the LED ?
If the flashgun had a longer decay your camera set on 2.5 secs would pick up both full flashed periods and if the Flashgun was longer
than the LED the resulting picture WOULD be exposed more anyway whether it was brightest or not ?

Or did you design both Flashes to be the same decay period ? Or perhaps Electronic flashguns have no decay ? (I don't know)
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Mr Mike
Posted 4/8/2012 07:47 (#97874 - in reply to #97871)
Subject: Re: LED Flash


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Location: Bury - In The Laboratory		I did not actually measure the flash time, but it will be in the order of 10's of ms. Probably a mistake, as I could have measured it and matched the LED exactly. Saying that, I roughly estimated it by manual control, the LED probably would have been on for longer. The flash looks to have a 'long' on time due to the eyes persistence of vision.
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moonwalker
Posted 4/8/2012 19:17 (#97876 - in reply to #97867)
Subject: Re: LED Flash


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Location: Near Edinburgh, Scotland.		Well if you want to prove it "in the interests of science" i suppose you could maybe measure each exactly by use of a photo cell and a scope perhaps to measure the light duration ? (or maybe it would need some sort of other time measuring device)

Maybe some way of extending the LED decay time would make up for its lack of Lumens punch. I suppose it would all depend on the Output curve for a given current over the discharge time.
Are two Cap values on each unit about the same valve, therefore discharge time would be the same if both loads were the same too ?
(Trying hard to remember all my electronic theory)
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Mr Mike
Posted 5/8/2012 10:12 (#97878 - in reply to #97876)
Subject: Re: LED Flash


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Location: Bury - In The Laboratory		Capacitance is totally different for both as we are trying to get an equal energy in, via 2 voltage extremes. One being low voltage and the other high. Flash tube getting its energy in via high voltage and the the LED via high capacitance. A flash tube may have 220uF @ 400V = 17.6J, LED 40000uF @ 35V = 24.5J, but I would really need to take the Sunpak apart and find out values.
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