Mired Shift
What is Mired Shift?
Mired is a measurement of colour temperature. Mired shift is a change in this value. Colour correction filters have a specific mired shift value (e.g -71). Colour temperature is defined as the temperature of an equivalent Black body radiator that exhibits that colour of light. Typical values are:
<cue table ripped from wikipedia>
| Temperature | Source |
|---|---|
| 1,700 K | Match flame |
| 1,850 K | Candle flame |
| 2,700–3,300 K | Incandescent light bulb |
| 3,350 K | Studio "CP" light |
| 3,400 K | Studio lamps, photofloods, etc. |
| 4,100 K | Moonlight, xenon arc lamp |
| 5,000 K | Horizon daylight |
| 5,500–6,000 K | Typical daylight, electronic flash |
| 6,500 K | Daylight, overcast |
| 9,300 K | CRT screen |
| Note: These temperatures are merely characteristic; considerable variation may be present. | |
</cue table ripped from wikipedia>
Why is it useful?
Knowing the mired shift you need allows you to select a filter to convert from any colour temperature to any other colour temperature. It means you are not limited to the standard conversions such as "tungsten to daylight" - especially as daylight can take many different values.
Another case where calculating the mired shift is useful is when you have a scene involving a lit candle and you want to simulate the light it gives off with a tungsten fixture. (this is a mired shift of +228 and the lee filters calculator suggests full C.T straw together with 1/4 C.T straw to give +202)
How do I calculate it?
<math>Mired Value = \frac{1000000}{Colour Temp}</math> and the shift is (temp wanted)-(temp we have) so:
<math>Mired Shift = \frac{1000000}{Colour Temp wanted}-\frac{1000000}{Colour Temp we have}</math>
so for the above tungsten to candle example:
<math>Mired Shift = \frac{1000000}{1850K}-\frac{1000000}{3200K}</math>
<math>+228 = \frac{1000000}{1850K}-\frac{1000000}{3200K}</math>
Mired shifts can be both positive and negative depending on if we are increasing or decreasing the colour temperature (+ decreases, - increases) To put it another way, positive shifts add orange, negative shifts add blue.
Other useful links
- Lee Filters Mired Shift Calculator. Will suggest filters to you. - This is the only way I've been able to get mired shift values from the Lee Filters website! ARG!
- Wikipedia on Mired