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FAQ: Mireds


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#1 David Bradley

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Posted 25 March 2007 - 07:56 PM

the mired value of a light source is equal to '1,000,000 / X' where x equals the colour temperature in Kelvin. Colour correction gels such as colour temperature blue (CTB) and Colour temperature orange (CTO) vary in intensity and can be purchased according to their mired value.

To work out the appropriate Mired shift value required to balance a light source to another of a different colour temperature or to your film stock simply divide 1,000,000 by the colour temperature in degrees kelvin for the original source (the one you wish to emulate perhaps) then do the same again for the other source and subtract its value from the original.

i.e.

1000000 / 5500 (photographic daylight) = 181 (approx)

1000000 / 3200 (Tungsten studio lamp) = 312 (approx)

181 - 312 = -131

-131 is the mired shift value of wratten 80A and is generally used to balance tungsten (3200k) to daylight (5500k).

Mired values correspond more effectively to our perception of colour than measuring in Kelvin. CC gels always have a mired value so its good to know a bit about it when purchasing your gels and filters. Using mireds allows the cinematographer to accurately emulate specific colour temperatures in a uniformed manner.

If your not satisfied with this explanation the internet is a good place to look but also check out the chapter on colour theory in Blaine Brown's 'Cinematography Theory and Practice' (2004).
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#2 kpv rajkumar

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Posted 13 August 2007 - 09:56 PM

hi, dave, let me chip in too and keep the fire going !
mired = micro reciprocal degree.
also, '.... equal changes in color temperature are not necessarily percieved as equal changes in color. a change of 50k from 2000k to 2050k will be a noticeable difference in color. for an equivalent change in color perception at 5500k, the color temperature would need to shift 150k and about 500k at 10,000k. for this reason the mired system has been devised........' (blaine brown, in his book 'motion picture & video lighting' )
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