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    How do you measure lumens?
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    I want to compare the lumen output of an instrument I have, for which there is no lumens value established, with another instrument for which the manufacturer has stated a lumen value.

    The tools I have to measure light are a Spectra incident meter and a spot meter.

    I have in hand the instrument without an established value. How can I measure its lumen output? Both instruments are LED arrays.

    Also, is there a way to determine color temperature without a temperature meter? Could I possibly use FCP and an HVX to determine color temperature, somehow comparing images of a captured white card illuminated with light sources of known and unknown temperature values?

    Thanks for any ideas.


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    Lumens are useless as a comparison spec. What you need to know is how many footcandles it outputs at what distance. Any professional light will list its photometrics, showing the footcandle output at varying distances.


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    Senior Member Indywannabe's Avatar
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    VidLED does not advertise footcandles for thier flat panel, but does provide lumens.

    Do you know what tungsten wattage might compare to the CoolLED for brightness?


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    VIDLED is showing lux at 6 feet, which is not quite the same as showing footcandles at a distance but it's good enough because he quotes the same statistic for competitors' lights so you can get an idea of how it performs at 6'.
    http://vidled.com/productspecifications.html

    One of the lights he tests against, the Bescor MPL-645, is a tungsten unit. It's way brighter and will go much further, but it's a spotlight. VIDLED makes a soft light. If you soften the MPL-645 to where it's throwing a comparable pattern, it brings down the footcandles but spreads 'em out. Even so, it's still quite a bit brighter, so -- in tungsten terms, maybe a VIDLED competes with a 25w bulb? But if you want daylight color, you'd need a 50W tungsten with dichroic filter.


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    Senior Member Indywannabe's Avatar
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    Thanks for the breakdown Barry.


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    C'mon guys - Wikipedia:

    http://en.wikipedia.org/wiki/Lux

    lumens measure light output of a source - not too useful for us.
    Lux and footcandles both measure light falling on an area - very useful.
    1 Footcandle = 10.764 Lux

    For all practical purposes 100 Lux = 10 Footcandles.

    For what its worth BTW - I haven't seen the vidled, but I have compared the LitePanel daylight spot version to my extremely cheap and funky $100 Sony 20W sungun (I forget the number - but its the one with 2 bulbs that takes a cheap "L" series battery) The sony with plenty of diffusion to match the softness of the Litepanel is at least double the output & probably more with wider spread. That's at tungstun of course. No dimmer though - that sucks. A Sony L batt can last well over an hour maybe 2.

    I don't know - everybody raves about those units but when I use a sungun -

    1. I want tungstun 95% of of the time Most daylight situations I can find a way to use a card- or the LED's are too dim anyway.

    2. I'm usually in an uncontrolled very dark situation - usually an event at night - where I often need to get a wide shot where i pull off the diffusion and blast the room trying desperately to see anything at all.

    Those little soft LED's sound great for the extra ambience of shooting close to people, but have no flexibility to get the bigger shot. They would be useless to me in most sungun situations.

    The dimmer is great though. The best for me is still a Frezzi with a dimmer. I don't even like the chimeras on them because they take too long to remove when you need the big shot. That's my 2 cents. I realize I'm bucking the tide though. Wish they put a dimmer on the Sony - hell I'd pay $200 anyday.

    Vidleds can be OK in a car, but then you might see them in the glass.


    Lenny Levy
    Last edited by Lenilenapi; 11-28-2007 at 07:15 PM.


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    #7
    Cinematography/Lighting Mod Ryan Patrick O'Hara's Avatar
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    Quote Originally Posted by Lenilenapi View Post
    C'mon guys - Wikipedia:

    http://en.wikipedia.org/wiki/Lux

    lumens measure light output of a source - not too useful for us.
    Lux and footcandles both measure light falling on an area - very useful.
    1 Footcandle = 10.764 Lux

    I was seeing how long this was going to go on until someone would mention the conversion... haha. It's simply just two different ways to measure the same thing... like feet and meters. (not the same conversion!)

    From what I understand Footcandle rating system seems to be more 'american' measurement unit while the Lux seems like the 'euro' unit preferred.

    I just got a bunch of photometric's from Arri and it was all in lux. Oh math!

    If cinematography wasn't infinite, I'm sure I would have found the end by now.


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