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 Spectral Color vs Temperature
Name: Christopher
Status: student
Age: 12
Location: N/A
Country: N/A
Date: 2001-2002


Question:
Do the different colors of the spectrum have different temperatures?


Replies:
Any object at temperatures above absolute zero emits radiation. Let us concentrate on an ideal "black body." This ignores the complexities associated with real bodies and surfaces.

The radiation emitted by a black body (or a real body) is not at a single color (wavelength). At a given temperature an object emits a broad range of radiation according to an equation known as Plank's Law, after Max Plank, the German scientist that discovered it.

Conversely, there is a range of temperatures at which a body emits a significant amount radiation at a particular color (wavelength). However, a body at a particular temperature gives off the largest fraction of its radiation at a particular wavelength (color). It is in this sense that one can say that different colors (wavelengths) have different temperatures.

Ali Khounsary, Ph.D.
Advanced Photon Source
Argonne National Laboratory


Christopher,

The colors do not have specific temperatures, they have frequencies. A frequency is how fast something vibrates. A light waves vibrates as it travels, rather like a wave traveling along water. Different colors correspond to different vibration frequencies. A hotter object can produce a more quickly vibrating light wave, and blue light has a higher frequency than red light. As a result, a blue flame is hotter than a red flame.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


I aguessing a bit about what your question means. Electromagnetic radiation, of which visible light is a small part, can generate heat if it is absorbed by some object, and this may increase the temperature. So in that sense light can be said to generate heat, but that is not usually meant to indicate that the light "has a temperature".

The more common way in which light and temperature are related is what is called "black body radiation". This is the radiation that you see when you turn on an electric stove and the burner glows red, but this is actually a continuous spectrum of light extending into the infrared. As the object is heated to a higher temperature this distribution of light wavelengths changes decreasing in the average wavelength, but still a continuous distribution of wavelengths. What your eyes perceive is that the "color" becomes more orange then yellow then bluer, and finally it becomes "white hot" when the temperature is so high that all wavelengths in the visible range 400 to about 700 nanometers have about equal intensity.

In photography, and other applications, you will sometimes see what is called a color temperature. What this term means is the temperature you would have to heat a "black body" to in order that the radiating object has the perceived color.

Vince Calder



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