Mired

Close up of the Planckian locus in the CIE 1960 color space, with the isotherms in mireds.

Close up of the Planckian locus in the CIE 1960 color space, with the isotherms in kelvins.

Note the even spacing of the isotherms when using the reciprocal temperature scale. The even spacing of the isotherms on the locus implies that the mired scale is a better measure of perceptual color difference than the temperature scale. The range of isothermal color temperatures for both diagrams is from 1000 K (1000 MK⁻¹) to 10000 K (100 MK⁻¹).

Contracted from the term micro reciprocal degree, the mired (/ˈmaɪrɛd/^[1]) is a unit of measurement used to express color temperature. Values in mireds are calculated by the formula:

${\displaystyle M={\frac {1\,000\,000\,{\text{K}}}{T}},}$

where T is the colour temperature in units of kelvins and M denotes the resulting mired dimensionless number. The constant 1000000 K is one million kelvins.

The SI term for this unit is the reciprocal megakelvin (MK⁻¹), shortened to mirek, but this term has not gained traction.^[2]

For convenience, decamireds are sometimes used, with each decamired equaling ten mireds.

The use of the term mired dates back to Irwin G. Priest's observation in 1932 that the just noticeable difference between two illuminants is based on the difference of the reciprocals of their temperatures, rather than the difference in the temperatures themselves.^[3]