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 Film Interference and Feathers
Name:  Sheng H.
Status: student
Age: 19
Location: N/A
Country: N/A
Date: 2000-2001


Question:
We all see the colourful wings of butterflies and beautiful feathers of ducks. How do u explain these "colour appearing" phenomenons on those animals by using thin film interference?


Replies:
Sheng,

When light hits two surfaces that have a separation (one behind the other) of about a wavelength, there can be a big interference effect in the reflected light. Some reflects from the front surface. Some reflects from the back surface. Because light from the back surface travels a little bit further than light from the front, it is shifted slightly. If back and front light waves line up with each other, you get constructive interference (peaks with peaks, valleys with valleys). That color is bright. If the waves are exactly out of line, you get destructive interference (peaks with valleys, valleys with peaks). That color is dim, possibly not visible at all. Only some colors interfere constructively. All colors hit the wing together in the sunlight. The film thickness determines which reflect brightly and which reflect dimly. Your eye "interprets" the combination as a specific color. Different parts of the wings have slightly different surface thicknesses.

Dr. Ken Mellendorf
Illinois Central College


I do not think that the colors in animals are created by thin film interference. Thin film interference occurs in transparent materials that have a thickness of about a wavelength of light -- that's less than one micrometer thick. I do not believe that butterfly wings or duck feathers are transparent enough, or thin enough, to do that.

-Wil



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