# BOUNCED LIGHT PHOTOMETRICS

5 replies to this topic

### #1 Al Ramis

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Posted 26 July 2008 - 10:10 AM

Hi everyone,

Just was wondering about the existence of a software, table or any other way to calculate the photometrics of a bounced light, for instance a 6K HMI bounced to a white board would give you whatever amount of lux...or footcandles..

Thanks in advance!!!
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### #2 Andrew Brinkhaus

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Posted 26 July 2008 - 01:15 PM

This would be very difficult for a program to calculate, if not impossible. There are too many variables involved to yield a reliable result. The distance of the light to the bounce, the density of the bounce, exact color would effect reflection, as well as the size and material type, whether it is foamcore, gryfflon, etc. Why not just meter the bounce of the light and use a table to convert your f/stop to FC's or lux?

Hi everyone,

Just was wondering about the existence of a software, table or any other way to calculate the photometrics of a bounced light, for instance a 6K HMI bounced to a white board would give you whatever amount of lux...or footcandles..

Thanks in advance!!!

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### #3 Ken Minehan

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Posted 27 July 2008 - 09:14 PM

Hi ramis, i dont know if this will help you. I think it is difficult to work out the lux or footcandles of bounced light but i did read on this forum this equation:

100asa@ f2.8= 100 footcandles.

and

1footcandle = 10.764 Lux

so i think as long as you have these 2 equations you can work out the intensities of light based on the photometrics provided by arri for example.

I have a shoot coming up tomorrow and i wanted to work out if my 5k fresnel was going to be enough. so i used this calculation.
I know that i'm working on 250asa, and that the 5k flood about 5 metres away was going to give me 3560 lux.
So with 1 footcandle =10.764 Lux, i can work out that i will have 330.73 footcandles.

therefore when 100asa@ f2.8=100 footcandles.
i can work out that the 5k flood at 5 metres away is going to be, 250asa @f5.6 1/3 =330.73 footcandles

I'm gonna put a silk in front of that which will take out 2 stops max,
so my key light will be f2.8 1/3.

Theoretically that should be right.

ken minehan
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### #4 Jonathan Bowerbank

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Posted 28 July 2008 - 12:03 AM

Does anyone (besides event lighting techs) really light by software? Besides drawing up a general placement of fixtures, I don't think you can get so specific with your diagrams or check your levels until you're on set and seeing the performances blocked out before you.
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### #5 Ken Minehan

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Posted 28 July 2008 - 12:51 AM

Yep, i totally agree with you Jonathon. On set there are 1001 variables to take in to consideration.

As with the equation i stated earlier it is a rough guide for someone like me with limited experience to be able to work out if the light you hire will be strong enough or not. Once you have enough experience and you know that a 5k 30ft away will give you a certain amount of light. Then of course you have no worries.

As for me I trying to work out 5k through a silk at a certain distance will be enough for my key. For this situation i felt, been able to work out was very helpful. especially when the shoot budget is quite tight and i dont have the luxury of renting things i wont use.

regards
Ken Minehan
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### #6 David Auner aac

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Posted 28 July 2008 - 02:03 AM

Does anyone (besides event lighting techs) really light by software? Besides drawing up a general placement of fixtures, I don't think you can get so specific with your diagrams or check your levels until you're on set and seeing the performances blocked out before you.

I think software and detailed lighting plans are more useful in TV studio situations or the like. Maybe too, if you prelight an interview space for your doco. Other than that I can't really imagine using software prior to being on the set.

Cheers, Dave
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