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Light lost through bounce


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#1 Jimmy Browning

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Posted 07 June 2007 - 05:24 PM

Has anyone ever compiled some photometric data for the amount of footcandles lost through bouncing light on various materials?

I know there are lots of variables. Intensity of the source, distance from the source to the bounce, distance from the bounce to the subject being illuminated, type and size of material, angle, and so on.

I know that light isn't actually "lost" through bouncing it. What I mean is, say I place my subject and the bounce material at a certain distance from each other, and the particular light source at a certain distance from the material. What would happen if I change materials? How many footcandles will I gain or lose on the subject's face? What if I change to a larger size material, but still keep the entire surface illuminated by the same source?

Precise calculations aren't necessary. What I'm looking for are some average ranges, to get a general feel for the relationships between the different variables. It would come in handy when coming into a lighting situation to have a general idea of what units and materials and distances would get me close to the footcandle level I'm looking for, without having to waste too much time experimenting on set.
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#2 robert duke

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Posted 07 June 2007 - 06:08 PM

I dont think there is an imperical way to calculate light loss from a bounce. Distance from reflector, angle of light, beam spread on the light, condition of the reflector, size of the reflector, size of the light all affect the light output. larger=softer, smaller =sharper for the bounce. The best way is to guesstimate the loss, if you want hard or soft bounce, directional or diffused.
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#3 Bob Hayes

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Posted 07 June 2007 - 08:57 PM

Jimmy

It?s not that hard to test it yourself. Select your bounce materials, Bead board, foam core, grifflon, Rosco scrim and select some different sizes. Then bounce a light into and take some readings. If you really want to get technical. Point the baby at the subject and spot it, flood it, place diffusion on the doors and on a frame. It would be a fun days worth of testing and you could probably get some friends to participate. Get a good looking model and shoot stills of your tests. Ultimately you will find that it is a real sense of feel that is developed through experimentation. Testing is a great way to start.

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#4 Jimmy Browning

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Posted 08 June 2007 - 03:47 PM

Jimmy

It?s not that hard to test it yourself. Select your bounce materials, Bead board, foam core, grifflon, Rosco scrim and select some different sizes. Then bounce a light into and take some readings. If you really want to get technical. Point the baby at the subject and spot it, flood it, place diffusion on the doors and on a frame. It would be a fun days worth of testing and you could probably get some friends to participate. Get a good looking model and shoot stills of your tests. Ultimately you will find that it is a real sense of feel that is developed through experimentation. Testing is a great way to start.



I probably will sometime this summer. If anyone's interested, I'll post about it afterwards.
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FJS International, LLC

Media Blackout - Custom Cables and AKS

CineLab

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