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-   -   lux, lumen, footcandles, how does it relate? (https://www.dvinfo.net/forum/photon-management/105069-lux-lumen-footcandles-how-does-relate.html)

Chris Klidonas October 5th, 2007 01:42 PM

lux, lumen, footcandles, how does it relate?
OK this is just all interesting, I get lux and lumen ratings all the time, and than ask well what settings would you be able to shoot at with that light? to which they respond that depends, so I give them the baseline iso of my camera, state no gain(+or-) the shutter speed I would prefer to shoot at and say so what f stop is you light putting out at thise settings? to which they respond well it depends! On what? the phase of the moon? whether or not Venus is in retrograde? If the president is doing a great job or not! what would it depend on??

I mean I am stating no additional modifiers, no diffussion, no gels, and I don't even care if you only know a baseline from a given shutter/iso/distance from there it can all be arranged and figured out mathamatically. They do not know.

So I ask if no one knows how much light you actually get for a given light/fixture/modifier combination, how do you know how much and what size lights to bring to a shoot?

Why is there no relationship in the video business? Why would'nt every compnay state that their lights produce x light at y speed at z iso using abc modifier or no modifier whatever the case may be??

On a side note why is it that every place you go with hotlight alternatives have a 500ws equivalent but that actual lumens/lux and actual light output varies almost 2 stops from some to others? What does it mean 500ws equivalent? one means 500ws of light behind glass the other means 500ws of light behind a black wall with a pinhole of an opening to let light through?

Its frustrating to buy anything online or even in stores since no one knows anything and no one has anything out on display to just check out.


Giroud Francois October 5th, 2007 03:34 PM

it is easy, it just require a lot of calculation that normal human brain do not want to deal with.
how the light is focused ? diffused ? reflected ? distance ? angle ?
a single bulb can give very different result in different place, so nobody will give you anything else than fuzzy specs or what the lamp is able to output.
you simply need to buy a light measurement tool (photo cell) , like they use on any movie stage since camera exists (or trust your camera information)

Chris Klidonas October 6th, 2007 11:48 AM

Thanks but I know about light meters, I work for a photographer who is known for his lighting, its not that, its how can I compare and decide on any lights before they are taking up space and producing not enough, or way, way, to much light for me? I mean I see one light selling saying 500w equivalent, and another and the lumens are different and after you buy them neither is anywhere near each other in actual usable light. Meaning at 6 feet 320iso, 1.48th second, one is producing f1.2 and one is f3.4 ? yet both claim the same, then I get another and try it and do not even have f 1.0? and yet other lights are claiming lets say 1000w and producing so much light that I have to ND the light or lens to shoot at anything near 3.4 at 1/48th at 320iso. does everyone just buy and send back that which does not work for them? or does everyone just live with whatever and make the best of it? always spend more on larger more powerful lights and gel them down? that means always carrying heavier than you need too and using more power than you need to.

I so wish someone would come up with at least a basic standard like at a given iso at a given distance and shutter speed light equals x Fstop! that way its just a matter of putting in your numbers and accounting for any gels/filters/modifiers, most of which (if not all) have ratings on how much light they cut from a source.

I cannot believe that an industry this advanced and large does not have such a system in place already.

Giroud Francois October 6th, 2007 12:06 PM

it exist, and it is the lumen.

The problem is the lumen is only a measure from the device (yes the old light meters is back again), so it gives no information about the device itself.
change the bulb, put in on 220V instead 110V and all is changed.
and the number of lumens you throw on a subject will give you no information about how much is coming back to the camera, so again the light meter is the king here.
that is probably too, why ligthing is an art....

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