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#1 Fra Farellacci

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Posted 02 February 2009 - 05:16 PM

Hi
I am working on a light installation in which I should demonstrate how primary colors create white light.
I am looking for gels to use on daylight light. I found at LEE's only primary red 106 and primary green 139. Ho close are they to the real primary colors ?
So no primary blue.
Do you know how I could easily produce primary color lights ?
Nota bene : it is ment for an installation and not for a shooting
Thanks
François

Edited by Fra Farellacci, 02 February 2009 - 05:20 PM.

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#2 Matthew Parnell

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Posted 03 February 2009 - 03:41 AM

Maybe RGB LED fixtures could be good for this?
Cheers,
Matt.
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#3 Fra Farellacci

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Posted 03 February 2009 - 05:09 AM

Didn't think about this. I'll investigate. Good idea !

Maybe RGB LED fixtures could be good for this?
Cheers,
Matt.


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#4 Jeff Locke

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Posted 03 February 2009 - 11:08 AM

The best way I have found to create this experiment is with three sperate lights with shutters. Point them at the same spot and open and close the shutters in different combinations to create different colors. As for the gels...LEE should all the primary colors, and when it says primary, it means it. The number is just a coding system that orders the colors. The other main company is Rosco, and they make primary gels as well. Also, if you want to be fancy about it you could get a primary yellow and show the difference between light primaries and pigment primaries. Good Luck.
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#5 Dominic Case

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Posted 04 February 2009 - 11:38 PM

LED sources would certainly give you the purest colours as they tend to have a very narrow wavelength set. Also, filtering white light absorbs at least 2/3 of the original light in each colour, - actually quite a lot more as no filter is 100% pure.

Most important if you want to demonstrate good colour mixing is to ensure that your lights project as uniform a spot of light as possible. Even-field red and green add together to produce a very convincing yellow for example: if the lighting is less uniform, you get a patchy reddish-greenish mess that doesn't impress in the same way at all. ( I tried this with a set of cheap (i.e. give-away) coloured LED flashlights, and it was disappointing).
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#6 John Sprung

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Posted 09 February 2009 - 05:43 PM

.... Ho close are they to the real primary colors ?


There are no absolute physical "real" primary colors. Any choice of a well saturated red, green, and blue will work fine for making a demonstration white.

Every color specification standard picks its own primaries, there are at least a dozen of them out there. Here are just a few:

CIE
Rec 709
Rec 601
PAL/SECAM/EBU
SMPTE C
SMPTE 240M
DCI 1.1
DC P7V2
Adobe RGB 98
ROMM

What you want to find out about is CIE 1931 (x,y) space. It describes normal human trichromatic vision, and it's the place where the standards people pick their primaries and white points.

Here's a place to start:

http://en.wikipedia....931_color_space

Scroll down to the diagram that looks like a shark fin with strong colors on it. That's (x,y) space.





-- J.S.
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