Mired

{{Multiple image|total_width = 480|direction=horizontal

| header = Close up of the Planckian locus in the CIE 1960 color space

| image1 = Planckian-locus-in-mireds.png

| caption1 = Isotherms in mireds

| image2 = Planckian-locus.png

| caption2 = Isotherms in kelvins

| footer = 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 {{val|10,000|u=K}} (100 MK⁻¹).

}}

Contracted from the term micro reciprocal degree, the mired ({{IPAc-en|'|m|aɪ|r|ɛ|d}}{{Cite book |url=http://alltootechnical.weebly.com/uploads/4/0/7/5/4075543/dict_units.pdf |title=How Many? A Dictionary of Units of Measurement |location=Pasig City |publication-date=20 March 2013 |pages=239 |language=en}}) is a unit of measurement used to express color temperature. Values in mireds are calculated by the formula:

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

where T is the colour temperature in units of kelvins and M denotes the resulting mired dimensionless number. The constant {{val|1,000,000|u=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.{{cite book |title=Colorimetry: Fundamentals and Applications |page=84 |first=Noboru |last=Ohta |author2=Robertson, Alan R. |isbn=0-470-09472-9 |publisher=Wiley |year=2005}}

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.{{cite journal |title=A proposed scale for use in specifying the chromaticity of incandescent illuminants and various phases of daylight |first=Irwin G. |last=Priest |journal=JOSA |date=February 1932 |volume=23 |issue=2 |pages=41–45 |url=http://www.opticsinfobase.org/abstract.cfm?URI=josa-23-2-41 |format=abstract |doi=10.1364/JOSA.23.000041}}

Examples

A blue sky, which has a color temperature T of about {{val|25,000|u=K}}, has a mired value of M = 40 mireds, while a standard electronic photography flash, having a color temperature T of 5000 K, has a mired value of M = 200 mireds.

class="wikitable"

|+Common color temperature and mired equivalents{{cite book |url=https://archive.org/details/tiffenpracticalf0000smit/ |title=The Tiffen practical filter manual |first=Robb |last=Smith |date=1975 |publisher=American Photographic Book Publishing Co., Inc. |lccn=75-21574 |isbn=0-8174-0180-6}}{{rp|40}}

! Light source !! Temp. (K) !! Mired

Skylight (clear, blue)

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|15000|hexval}}|#{{Color temperature|27000|hexval}}|direction = right}} | 15000–27000

{{#expr:10^6/27000 round -1}}–{{#expr:10^6/15000 round -1}}

Shade, illuminated by skylight

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|10000|hexval}}|#{{Color temperature|12000|hexval}}|direction = right}} | 10000–12000

{{#expr:10^6/12000 round -1}}–{{#expr:10^6/10000 round -1}}

Skylight (hazy)

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|7500|hexval}}|#{{Color temperature|8400|hexval}}|direction = right}} | 7500–8400

{{#expr:10^6/8400 round -1}}–{{#expr:10^6/7500 round -1}}

Overcast

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|6700|hexval}}|#{{Color temperature|7000|hexval}}|direction = right}} | 6700–7000

{{#expr:10^6/7000 round -1}}–{{#expr:10^6/6700 round -1}}

Electronic flash

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|6200|hexval}}|#{{Color temperature|6800|hexval}}|direction = right}} | 6200–6800

{{#expr:10^6/6800 round -1}}–{{#expr:10^6/6200 round -1}}

Sunlight (hazy)

| class="mw-no-invert" style="background:#{{Color temperature|5800|hexval}}" | 5800

Daylight (average)

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|5500|hexval}}|#{{Color temperature|6000|hexval}}|direction = right}} | 5500–6000

{{#expr:10^6/6000 round -1}}–{{#expr:10^6/5500 round -1}}

Daylight (morning / afternoon)

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|5000|hexval}}|#{{Color temperature|5500|hexval}}|direction = right}} | 5000–5500

{{#expr:10^6/5500 round -1}}–{{#expr:10^6/5000 round -1}}

LED (cool white){{cite web |url=https://www.westinghouselighting.com/color-temperature.aspx |title=Understanding color temperature |publisher=Westinghouse |access-date=18 August 2024}}

| class="mw-no-invert" style={{Linear-gradient background|#{{Color temperature|3100|hexval}}|#{{Color temperature|4500|hexval}}|direction = right}} | 3100–4500

{{#expr:10^6/4500 round -1}}–{{#expr:10^6/3100 round -1}}

Professional tungsten

| class="mw-no-invert" style="background:#{{Color temperature|3200|hexval}}" | 3200

Incandescent bulb (100 W)

| class="mw-no-invert" style="background:#{{Color temperature|2900|hexval}}" | 2900

Incandescent bulb (40 W)

| class="mw-no-invert" style="background:#{{Color temperature|2650|hexval}}" | 2650

Applications

= Photographic filter and gel =

File:Color temperature - mired shift.svg]]

In photography, mireds are used to indicate the color temperature shift provided by a filter or gel for a given film 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, one would need a corrective filter or gel providing a mired shift

: $\frac{10^6}{5700} - \frac{10^6}{3200} \approx -137~\text{MK}^{-1}.$

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}}{{cite web |title=Mired Shift Gel Table |url=https://www.danberens.co.uk/uploads/3/0/0/6/30067935/mired_shift_gel_and_camera_filter_tables.pdf}} Color gels with negative mired values appear green or blue, while those with positive values appear amber or red.

= CCT calculation =

A number of mathematical methods, including Robertson's, calculate the correlated color temperature of a light source from its chromaticity values. These methods exploit the relatively even spacing of the mired uint internally.{{cite journal|title=Computation of Correlated Color Temperature and Distribution Temperature|first=Alan R.|last=Robertson|journal=JOSA|volume=58|issue=11|pages=1528–1535|date=November 1968|doi=10.1364/JOSA.58.001528|bibcode=1968JOSA...58.1528R}}

= Color description =

Apple's HomeKit uses the mired unit for specifying color temperature.{{cite web |title=HMCharacteristicTypeColorTemperature |url=https://developer.apple.com/documentation/homekit/hmcharacteristictypecolortemperature |website=Apple Developer Documentation}}

References

Category:Units of measurement

Category:Non-SI metric units

Category:Color