Amount of light?

Christopher Norin · April 30, 2011

Hi!

I'm looking for a relatively simple way of calculating the amount of light I would need to illuminate any given area. Ofcourse, thus depends on many factors; size of the area, how far away the lights need to be etc. Given that you know these two factors, how would you calculate the wattage and number of lights?

I've looked around but haven't been able to find a simple way of going about it,

I would appreciate any help you could provide.

Best,

Christopher

Christopher Norin · April 30, 2011

I want to add that I've been using pCam's scene illumination but it doesn't tell me how much light I would need to light an area of any given size. As far as I can tell at least.

Adrian Sierkowski · April 30, 2011

I'm not really sure I understand what you mean. For example, you walk into a room and say, oh, ok, i Want to be at an F4, then you have to figure out your film stock, let's say 500T, '19, which means you'd need 40FC for the room.

But, if you're looking for what light to use to get 40FC there is no correct answer, it depends upon style...

So in essence, you are the one who says how much light you need for any given area. And it'll take experience and time to know which lights you'd use for which situation. You'll have to know how much light is required for what stop you're at on which system you're using first, then you'll have to know which lights can producer that much light at that distance (normally available upon a manufacturer's website,) and then youll also need to factore in if you can fit the light into your given area (for example, I highly doubt you could fit an 18K into a small bathroom).

Christopher Norin · April 30, 2011

Adrian, I appreciate your answer. It helped me a lot!

Christopher

Hal Smith · April 30, 2011

ETC has great photometric information for their different Source Four models on their website. Reading through some of the specs will give you a good idea what professional photometrics data and diagrams look like.

Dig down through to the data sheets for individual fixture models like the 50 degree Source Four.

http://www.etcconnect.com/products.fixtures.aspx

Chris Millar · April 30, 2011

You can do the math for an ideal point source kinda easy (inverse square law) - but no real life situation ever really approaches this, there is so much bounced/reflected/diffuse light about so as to make the math a bit silly...

Maybe one open lamp, no reflectors or diffusion or otherwise on a blacksand beach or theatre stage and you'd be pretty sweet with the inverse square law

I think most DoP's go with experience - so you just gotta get in there, take notes.

Its interesting in that reading up on the complexities of realistic 3D rendering can shed light (guffaw) on the real world situation:

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

Christopher Norin · May 2, 2011

Great! I'm really trying to get an understanding of this.

I have a project in the near future where I'll need to light a 450x450 feet area. I don't yet have the experience to know what I need to bring to have it covered. Therefor, a simple way of calculating amount of I need for a given helps immensely.

Thanks again!

Christopher

Adrian Sierkowski · May 2, 2011

http://www.arri.de/l...calculator.html

for that large of an area, you're in the big HMI range.

an 18KW HI 450ft i on the middle of it's "spot flood" should give you a T1.8 on 500 speed film (8 fc) in the middle of the beam and the overall cone of the light would be 240 ft, or so. So 2 18KW HMIs overlapped would light up your space but it wouldn't necessarily be very interesting, and this of course would have to be night.

Matt Dennie · May 6, 2011

I use the arri calculator all the time. It is my main resource for figuring out how much power I will need for a location. I generally aim for about 120fc to account for diffusion. I usually end up with T4 with iso 400.