Color temperature is a visible color characteristic of a light source, it is calculated by determining the temperature of the light on an isotemperature line on the chromaticity chart, related to a black body locus, the unit is in absolute temperature Kelvin (K). It is not to be mistaken as the actual temperature (heat) that emits from any light source.
*Black body locus or Planckian locus is the path line that the color of an incandescent black body would take in the CIE 1931 chromaticity diagram as temperature changes/shift. It begins from reddish at low temperatures through orange, yellowish white, white, and bluish white at high temperatures.
The term, color temperature is only used to quantify color of a light source that correspond closely to the radiation of a black body locus, e.g., color temperatures over 6,000K are called cool colors (bluish white), while lower color temperatures (1,500–3,500 K) are called warm colors (reddish color to yellowish white). Color temperature is not suitable to be use for a green light or a purple light as these colors do not fall within the black body locus. Color temperature is an important factor for applications like lighting, photography, videography and other fields that involves lighting.
Using the sun as an example, as the sun crosses the sky from morning to evening, the color of sunlight appears to be different. It can be red, orange, yellow or white depending on its position. Sunlight changes color over different times of the day, this is a result of the scattering of light, and it is not due to changes in black-body radiation. For each color of the sunlight, the color temperature is different, e.g. the morning sun has a correlated color temperature of 2000K – 3000K (orange/reddish to warm white), in the noon it is at 5500K – 6500K (white or cool white) and in the evening the color temperature drops back to 1850K – 2000K.
About the Author: Garie Xu
Garie Xu is the Sales Engineer of Konica Minolta Sensing Singapore Pte Ltd. Graduated from a manufacturing engineering background, he is mainly involved in sales, seminar, training and coaching in the field of light and color management. With his prior 3 years’ experience in the oil and gas industry and 2 years in Konica Minolta, he is providing solutions to the many industrial applications. He has also conducted seminars and workshops to educate the industry on instrumentation technologies and color science.