Contracted from the term micro reciprocal degree, the mired is a unit of measurement used to express

color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...

. Values in mireds are calculated by the formula: :

M = \frac,

where ''T'' is the colour temperature in units of

kelvins The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phy ...

and ''M'' denotes the resulting mired dimensionless number. The constant is one million kelvins. For convenience, ''decamireds'' are sometimes used, with each decamired equaling ten mireds. The SI term for this unit is the reciprocal megakelvin (MK⁻¹), shortened to ''mirek'', but this term has not gained traction. The use of the term ''mired'' dates back to Irwin G. Priest's observation in 1932 that the

just noticeable difference In the branch of experimental psychology focused on sense, sensation, and perception, which is called psychophysics, a just-noticeable difference or JND is the amount something must be changed in order for a difference to be noticeable, detectable ...

between two

illuminant A standard illuminant is a theoretical source of visible light with a spectral power distribution that is published. Standard illuminants provide a basis for comparing images or colors recorded under different lighting. CIE illuminants The Inter ...

s is based on the difference of the reciprocals of their temperatures, rather than the difference in the temperatures themselves.

Examples

A blue sky, which has a color temperature ''T'' of about , has a mired value of ''M'' = 40 mireds, while a standard electronic

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed ...

flash Flash, flashes, or FLASH may refer to: Arts, entertainment, and media Fictional aliases * Flash (DC Comics character), several DC Comics superheroes with super speed: ** Flash (Barry Allen) ** Flash (Jay Garrick) ** Wally West, the first Kid ...

, having a color temperature ''T'' of 5000 K, has a mired value of ''M'' = 200 mireds. In

, mireds are used to indicate the color temperature shift provided by a

filter Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...

gel A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state, although the liquid phase may still dif ...

for a given

film A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...

and light source. For instance, to use daylight film (5700 K) to take a photograph under a tungsten light source (3200 K) without introducing a

color cast A colour cast is a tint of a particular colour, usually unwanted, that evenly affects a photographic image in whole or in part. Certain types of light can cause film and digital cameras to render a colour cast. Illuminating a subject with light s ...

, one would need a corrective filter or gel providing a mired shift :

\frac - \frac \approx -137~\text^.

This corresponds to a color temperature blue (CTB) filter.{{cite book , url=https://books.google.com/books?id=1JL2jFbNPNAC&q=ctb+159+mired&pg=PA172 , title=Cinematography: Theory and Practice : Imagemaking for Cinematographers , first=Blain , last=Brown , isbn=0-240-80500-3 , page=172 , publisher=Focal Press , year=2002 Color gels with negative mired values appear green or blue, while those with positive values appear amber or red.

References

Units of measurement Non-SI metric units Color