Download Don Werthmann The Kelvin Scale Defines the Color

Washtenaw Community College
Don Werthmann
The Kelvin Scale Defines the Color Temperature of Light
Cooler Light Source
13,000 K
Blue sky, no direct sun: 11,000 K to 13,000 K
12,000 K
11,000 K
10,000 K
9,000 K
8,000 K
Overcast Sky: 8000 K
7,000 K
6,000 K
Average Daylight: 6500 K
Electronic Flash: 6000 K
5,000 K
Noon Sunlight: 5500 K — DAYLIGHT
Film viewing tables, projector bulbs, HMI Lighting
4,000 K
Studio Light, Type A: 3400 K
Studio Light, Type B: 3200 K — TUNGSTEN
Household Lightbulb: 2800 K
3,000 K
2,000 K
Candlelight: 1900 K
1,000 K
Warmer Light Source
Kelvin (K) defines a specific property of light that is emitted by a star or other astronomical object.
A black body—known as absolute zero or 0 K—is a theoretical stellar object that has a surface
which absorbs incident radiant energy but cannot reflect any (light). The scale interprets the degree
to which a black body would have to be heated for it to emit light of a given color. The Sun at mid-day
emits a color temperature of 5500 K (white light) and is the standard that color photographic materials,
image input devices, analog or computer processing equipment, and output devices are manufactured.
The illustration above interprets commonly used color temperatures of light. Note that ordinary ideas
of color—the warmth or coolness of thermal temperature—don't match what you think it to be.
Although red is known as a warm color, the color temperature of red/warm light is LOW on the
Kelvin Scale. Similarly, blue is known as a cool color but its color temperature is HIGH. The illustration
below compares the relativity of the Kelvin and Fahrenheit scales.
5,500
7,500
0 373 3,200
Kelvin
Black
°Fahrenheit
-460 212
15,000
30,000
45,000
Sun
9,980
60,000
Hottest Stars
26,540
53,540
80,540
—Text adapted from Sears and Zemansky’s University Physics, 6th Edition, pg. 323
—Illustration adapted from Astronomy: From the Earth to the Universe, 2nd Edition, appendix 13
107,540