Film-Tech Forum ARCHIVE: fL and lumen calculator

This is topic fL and lumen calculator in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Philip Borgnes (Member # 2383) on 04-22-2004, 05:53 PM:

Hi all,

I'm a newbie to this site and have been reading alot waiting for my registration to be approved so I'm very glad to be making my first posting.

Anyway, I'm starting up a small outdoor cinema and one of the questions I had was how bright a projector do I need and what size screen could I project that onto and still have it look good. After reading through many posts here I learned about the 16fL SMPTE spec. and the relationship of fL to Lumens. So out of that I created a spreadsheet that calculates these relationships.

I hope what I created is correct. If so it may help other newbies such as myself trying to figure this out. From what I calulated, my 2500 lumen projector will work great with my target 10x20 screen.

Thanks again for a great forum and am glad to join.

www.film-tech.com/ubbpics/fl.xls

[ 04-28-2004, 12:33 PM: Message edited by: Philip Borgnes ]

Posted by John Pytlak (Member # 331) on 04-22-2004, 09:56 PM:

For a matte white (gain = 1.0) screen, you want at least 12 footlamberts. So the image area (in square feet) x 12 fL will give an approximation of the "true" lumens required. But if you are cropping or letterboxing the image from the native display aspect ratio, some of the "true" lumens never reach the screen. Likewise, the light output specs of the projector are often optimistic, especially as the lamps age and light output decreases.