Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Color and Color Temperature
Name:  Craig
Status: other
Age: N/A
Location: N/A
Country: N/A
Date: N/A


Question:
What is color and how does it differ from color temperature?



Replies:
Dear Craig,

The color of a given light source is determined by the frequency or the light or, equivalently, by its wavelength. The frequency is the number of oscillations per second and the wavelength is the distance light travels in one complete oscillation. Visible light varies between red light, with a wavelength of 700 nm and a frequency of 430 trillion Hz and violet with a wavelength of 400 nm and a frequency of 750 trillion Hz. A nm is a billionth of a meter and a Hz is 1 oscillation per second. If the light includes several frequencies, the eye will interpret the light as having several colors, but usually combine them as, for example yellow and blue are seen as green. All colors combined are seen as white.

Color temperature is more complicated. If you have a black body at a certain temperature, that body will radiate a continuous spectrum whose average frequency increases with the temperature. Since red is the lowest frequency light, when you heat something up, it will first glow red. When it is hot enough so it emits all frequencies roughly equally, it glows white hot. So the temperature of a glowing body, such as an incandescent bulb can be determined by its color. That temperature is then called the color temperature since it determines the color of the light emitted by the bulb.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory