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Light Source Color Temperatures

The spectral quality of light used to create an image is a factor of filter spectral characteristics, illumination color temperature and subject reflectance. The spectral characteristics of the lighting will effect spectral selectivity imaging efforts. The following tables provide color temperature values for some common light sources. Color temperature is specified as degrees Kelvin and in MK-1 values (see table below for common conversion factors).


DAYLIGHT COLOR TEMPERATURES
Description Degrees Kelvin MK-1 Values
Clear Blue Sky
8000 to 27,000
125 to 037
Rainy, Misty Daylight
7200 to 8500
139 to 117
Overcast Daylight
6500 to 7200
154 to 139
Direct Sun + Clear Blue Sky
5700 to 6500
175 to 154
Summer Sunlight (9am to 3pm)
5400 to 5700
185 to 174
Summer Sunlight (before 9am or after 3pm)
4900 to 5600
204 to 179
Electronic Flash (Typical)
6200 to 6800
160 to 150


ARC LAMP COLOR TEMPERATURES
Description Degrees Kelvin MK-1 Values
Xenon Arc (unfiltered)
6000
167
White Flame Carbon Arc
5000
200
Yellow Flame Carbon Arc
3200
312


FLUORESCENT LAMP COLOR TEMPERATURES (Approximate)
Description Degrees Kelvin MK-1 Values
'True Daylight' Color Match Tubes
6500
154
'Daylight' Cool White Tubes
4300
233
'Warm White' Tubes
3000
333


Daylight Fluorescent



Cool White Fluorescent



White Fluorescent



Warm White Fluorescent



TUNGSTEN COLOR TEMPERATURES (Approximate)
Description Degrees Kelvin MK-1 Values
Photoflood & 3400K Tungsten-Halogen
3400
295
Tungsten-Halogen and Photolamps
3200
312
Projection Lamps (500 to 1000 Watts)
2900 to 3000
345 to 335
General Purpose Lamps (200 to 500 Watts)
2900
345
Household Lamps (100 to 150 Watts)
2850
350
Household Lamps (60 Watts)
2800
357
Household Lamps (40 Watts)
2750
360


Daylight and tungsten illumination will produce different spectral sensitivity plots on panchromatic film. The following illustration shows the tungsten and daylight spectral sensitivity plots for a typical panchromatic emulsion.



The spectral energy plots for tungsten and sunlight illumination are also different. Tungsten illumination is much "warmer" and contains much more energy in the red portion of the spectrum. Sunlight has more energy in the "cooler" or blue portion of the spectrum. The following illustration shows spectral energy plots for sunlight and two types of tungsten illumination.



The color temperature of tungsten lamps varies with line voltage. The following table shows how the color temperature of a 3200 degree Kelvin lamp varies with changes in line voltage.



Water acts like a blue pass band filter. The following illustration shows the absorption density curve for sunlight entering water (depth in feet and meters).




CANDLE COLOR TEMPERATURES (for Reference)
Description Degrees Kelvin MK-1 Values
Standard Candle
2000
500
Candle Flame
1500
660


Color Temperature Conversion Factors - The following list provides color temperature conversion factor equations. MK is the modern term for "Mired" which stands for micro-reciprocal (or the reciprocal of degrees Kelvin times 1,000,000).
Value: Equation:
Mired = MK-1
Decamired = mired / 10
Decamired = 100,000 / Kelvin
Mired = 10 * decamired
Mired = 1,000,000 / Kelvin
Kelvin = 100,000 / decamired
Kelvin = 1,000,000 / mired



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C1997 by Ed Scott - <dotted.dog@worldnet.att.net>
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