When a block of tungsten is heated, it produces light, just like the burner element of an electric stove.
As the temperature of the block increases, the color of the light goes from red to blue.
The Commission Internationale de l'Eclairage (CIE) measured the color of daylight in Washington D.C. at noon on the vernal equinox in 1931.
The daylight color was the same color of a block of tungsten heated to 4,870°K.
The CIE then developed a color temperature scale based on this intersection of the color of daylight and the color of a heated tungsten block
The 4,870°K temperature was rounded to 5,000°K.
In your camera, the sun icon uses the 5,000°K, or a similar value.
Most flashes also produce 5000°K light.
Here is a chart of the color temperatures of common light sources.
|Color||Light Source||Color Temperature||White Balance Icon||Mired||Kodak Wratten Filter|
|Candle flame||1,500 °K||667|
|40-watt bulb||2,750 °K||364|
|60-watt bulb||2,800 °K||357|
|100-watt bulb||2,850 °K||351|
|200-watt bulb||2,900 °K||345|
|500-watt bulb||3,000 °K||333|
ECA (250 watt)
BAH (300 watt)
ECT (500 watt)
|3,200 °K||Light bulb||313||80A|
|Quartz-halogen lamp||3,200 °K||313||80A|
BBA (250 watt)
EBV (500 watt)
BCA (250 watt)
EBW (500 watt)
|Morning & afternoon sunlight||5,000 - 5,500 °K||Sun||200 - 182|
|Overcast sky||6,700 - 7,000 °K||Clouds||149 - 143||81C - 81D|
|Shade||10,000 - 12,000 °K||Building with shadow||100 - 83||85C - 85|
|Clear sky||15,000 - 27,000 °K||67 - 50||85 - 85B|
There's a problem with the above color temperature system.
Any given change in color temperature produces a greater change in color at the lower temperatures than it would at higher temperatures.
For example, a change from 3,000°K to 3,100°K produces a greater change in the color, than a change from 6,000°K to 6,100°K.
The mired color temperature system solves this problem, using the mired unit of measure.
Mired is the acronym for micro-reciprocal degrees.
A mired is calculated by multiplying the inverse of the color temperature (°K) by 106.
1 ÷ color temperature (°K) x 1,000,000
Mired values are given in the above chart.
Filtration is determined by subtracting the mired value of the light source, from the mired value of the white balance setting.
For example, let's say you're photographing scene lighted with candles.
The mired for candlelight is 667.
You've set your white balance to the tungsten setting (light bulb icon), which has a mired of 313.
Subtracting the two mired values, 667 - 313, gives you the correction needed, 354 mired.
You need to cool the color of the candlelight, so you'd use a mired blue filter with a mired of 354.
Mired filters are either amber, to warm the color temperature, or blue, to cool the color temperature.
You may be able to adjust the white balance on your camera using mireds.
See the far right column of the above chart for Kodak Wratten filters.