Output of a camera flash in lumens?

RoyJ

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Camera flash power varies widely, but let's say it's a full size SLR flash with a guide number of 150', then it's probably comparable to a 3000 watt halogen studio light. Say 30,000 lumens, roughly?

Anyone have a more accurate guess?
 

paulr

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OK, let's say we're talking about a fairly serious shoe-mount SLR flash, the big units that mount on top of the camera, not the even bigger external studio strobes but also not the little dinky flashes built into pocket cameras.

The Nikon SB800 has a guide number (in meters) of 125 at ISO 100 with its zoom head set to telephoto (105mm coverage). That's a "beam angle" of 20x27 degrees (http://www.scantips.com/speed2.html) and the flash duration is 1/1050th second (same link). 20x27 degrees is about .35x.47 radians or .35*.47/(4*pi) steradians (is that right?) or 0.013 steradians.

The 125 guide number means at 1 meter you'd use f/125 (close to f/128) so this is 4x the exposure of f/64, the smallest aperture on this scale:
http://www.kodak.com/cluster/global/en/consumer/products/techInfo/am105/am105kic.shtml

Since that Kodak table shows f/64 to correspond with 64300 lux at 1/30th of a sec, 4x that would be about 257000 lux at 1/30th. But the flash is putting out that much light in 1/1050th sec so it's (1050/30)=35x brighter! That's 9 million lux!

However, because of that 20x27 mm narrow angle, that light is going over just 0.16 or so square meters. So spreading it out to 1 square meter (remember lumens = lux/square meter) we get 9 million * 0.16 or about 1.4 million lumens!

Remember that this is a fairly hefty 4AA-powered flashlight which will give you maybe 100 flashes on full power per set of batteries, or a total runtime of around 1/10th of a second. If you dialed the power back by a factor of 10000 so you were getting just 143 lumens (a more normal 4aa or 2x123 flashlight) the resulting 17 minute (10000 * 1/10th sec) runtime wouldn't be all that impressive, so the efficiency of these flashes is not that high. Of course you can't really dial back the power like that and get the same efficiency, that was just for comparison.

Cool question! Anyone up for checking the answer please do so, I could have easily made a mistake. It was fun researching this.
 
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IMSabbel

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Your numbers look about right.

Some quick googling gave that pdf about cell phone camera flashes: http://www.cap-xx.com/news/CAP-XX_LED_Flash_and_Xenon_Comparison.pdf

There they make notice that the small xenon bulbs have flash-times in the order of 50 us, thus allowing a 100 lumen 100msec led pulse to be compareable.

This would translate to peak brightness in of about 200,000 lumen for cell phones, and orders of magnitued more for big systems.

( like those guys :http://www.meggaflash.com/ , if you absolutely want to light up some valley in the night or something (see here: http://www.meggaflash.com/Sustut River Bridge photographed using meggaflash flashbulb2.htm )).
 

IsaacHayes

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Anyone know of any links for DIY of taking a bunch of disposable camera flash circuits and hooking them up to one powersource and firing them all at once? I think that would be pretty cool with a huge array of them. Say 5x5? :D
 

paulr

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Those disposable things are very weak compared with a bigger flash. 25 of them might come out about the same as the SB800 mentioned above. Sure the SB800 costs 300 bucks or so, but that's mostly because of the computerized innards, not the raw flash power. A comparably powerful simpler flash from Sunpak or Vivitar is in the 50 buck range. Or you can get a cheap AC-powered studio strobe that's several times as powerful, for maybe 100 bucks.
 

IsaacHayes

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Hmm good info. I think it would be cool to have a portable flash that would make it seem like lighting struck outside. :)
 

Burgess

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For a LOT of lumens, with relatively low cost and complexity,
get yerself' a few FLASHBULBS ! :grin2:


Even the humble #5's could make considerable light. :poof:


Flashbulbs are still available if you look for 'em.


There's a fellow on the web . . . .

Bill Cress is his name.

His website is Flashbulbs.com



I'm 54 years old, and i well remember using flashbulbs
(at times) up until the early 1970's. :candle:


Not to mention, my first camera was a Kodak Brownie Fiesta, (Christmas 1962), :santa:
which took those dinky little AG-1 flashbulbs.

Taking a "flash picture" practically doubled the cost of each photograph. :broke:


And ya' know . . . .

35 years later, i can STILL remember the sound and smell
of a flashbulb igniting. :cool:


Yes, this is an interesting thread !

:wave:

_
 

paulr

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I remember figuring out that the output of a good sized shoe-mount electronic camera flash was around 100,000 lumens, for around 1 millisecond.
 

KevinL

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My conservative calculations..

Little hotshoe flashes range from 50-100 watt-seconds. Let's take a median, 75WS. That's the power rating, spread over one second.

Flash pulses have a duration of 1/1000 or thereabouts. So that's 75 / 1/1000 = 75000 watts in that instant of a second.

Conservatively, assuming we get 10 lumens per watt, 75000 x 10 = 750,000 lumens.

It sounds crazy.
 
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LEDAdd1ct

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I remember seeing a device (of course I can't recall the URL right now, 'cause life's like that) which was essentially a camera flash being run off a battery. It didn't have constant on, but it would flash every so many seconds, probably after the capacitor charged. If I can remember the site, I'll post the link here.
 

KevinL

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I remember seeing a device (of course I can't recall the URL right now, 'cause life's like that) which was essentially a camera flash being run off a battery. It didn't have constant on, but it would flash every so many seconds, probably after the capacitor charged. If I can remember the site, I'll post the link here.

Little battery powered strobe signal light running on a D battery? There's one at countycomm.com. It's a bit wimpy though, I had one.
 

dpullum

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In reply to your 5x5 aray of flashes, I have the same DIY type of brain. In addition to making a ring flash or zapper with a g of 250, 5x5xg of 10, I have considered using a large capacitor and a large Strobe bulb. Both low cost on electronic gold mine ... like $2 for the pair. Shipping messes up the price, so for a DIY there are lot of thing for the junk drawer the bring the cost per item down.

I do MACRO, and so the lumens per sq feet is the key. there are LED flash lights that have 50 and 100 lumens , so for close work the light is intense enough to do a good photo even with the drug store flash lites. I made a simple rig, #10 wire embeded in a small plastic ware filled with Plaster of Paris and 3' to the end where a LED flash lite is attached. Makes great MACRO Studio Lite. d/p Don
 

bp_968

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Funny you mention sb800s. I have 4 of them and a 700 and 900. I fired 3 of them in my yard for some photos and it was really intense at night. I've also caught a 1/2 power shot from a sb800 in the face at 6" and it burned my eyes, sucked.

If you can think of any cool tests or demos I could do with them all let me know. Maybe a comparison against a led light or something at the same camera settings VS all 6 units at full power ;)

BP


OK, let's say we're talking about a fairly serious shoe-mount SLR flash, the big units that mount on top of the camera, not the even bigger external studio strobes but also not the little dinky flashes built into pocket cameras.

The Nikon SB800 has a guide number (in meters) of 125 at ISO 100 with its zoom head set to telephoto (105mm coverage). That's a "beam angle" of 20x27 degrees (http://www.scantips.com/speed2.html) and the flash duration is 1/1050th second (same link). 20x27 degrees is about .35x.47 radians or .35*.47/(4*pi) steradians (is that right?) or 0.013 steradians.

The 125 guide number means at 1 meter you'd use f/125 (close to f/128) so this is 4x the exposure of f/64, the smallest aperture on this scale:
http://www.kodak.com/cluster/global/en/consumer/products/techInfo/am105/am105kic.shtml

Since that Kodak table shows f/64 to correspond with 64300 lux at 1/30th of a sec, 4x that would be about 257000 lux at 1/30th. But the flash is putting out that much light in 1/1050th sec so it's (1050/30)=35x brighter! That's 9 million lux!

However, because of that 20x27 mm narrow angle, that light is going over just 0.16 or so square meters. So spreading it out to 1 square meter (remember lumens = lux/square meter) we get 9 million * 0.16 or about 1.4 million lumens!

Remember that this is a fairly hefty 4AA-powered flashlight which will give you maybe 100 flashes on full power per set of batteries, or a total runtime of around 1/10th of a second. If you dialed the power back by a factor of 10000 so you were getting just 143 lumens (a more normal 4aa or 2x123 flashlight) the resulting 17 minute (10000 * 1/10th sec) runtime wouldn't be all that impressive, so the efficiency of these flashes is not that high. Of course you can't really dial back the power like that and get the same efficiency, that was just for comparison.

Cool question! Anyone up for checking the answer please do so, I could have easily made a mistake. It was fun researching this.
 

bp_968

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Messages
48
You do realize the post you quoted above was posted 4 years ago?
Norm

It showed up as a new post in tapatalk so I responded. I guess the poster on the 31st necroed it and I got suckered via tapatalk lol.

And do you usually ask questions you know the answer to? ;)
 

Secateurs

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Apr 3, 2007
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My conservative calculations..

Flash pulses have a duration of 1/1000 or thereabouts..

I know this is an old thread, but I've just been thinking about it... if flash pulse is 1/1000s but you only want to shoot at 1/250s that means you only need 1/4 the lumens using a continuous light than you would a conventional flash to get the same amount of light into the camera. So we only need 200,000 lumens? Getting closer....

And how can we not be completely and permanently blinded if a large conventional studio flash puts out 200megalumens?
 
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