Experiment #1 Properties of Color

Introduction

Who knew that lasers were useful to demonstrate some of the most fascinating properties of the universe? Well, the keen staff at NOVAlasers did! And, of course, we’re always excited to share our knowledge!

Look around you. You’re surrounded by color. So much so, that most of us stop thinking about it! The human brain tends to simplify things for us and unless we pause and think, color sometimes seems like an intrinsic property of an object itself. Color, though, is a combination of the properties of an object, the light source striking that object, and the sensory information received by our eyes and interpreted by our brain. In short, the reason that an object is colored red, for example, is that when white light (sunlight or light from a light bulb) strikes that object only the red wavelength is reflected back into our eyes. The rest of the wavelengths are absorbed by the object. The reason that an object appears white is because it reflects all of the wavelengths back into our eyes, and absorbs none. Our eyes then interpret the combination of wavelengths reflected back as the color white.

So color then, is not really an intrinsic property of an object itself, but a combination of the properties of an object and the sensory perception of our eyes and brain. We learn to associate color names such as white, blue, etc early on in life because others teach these color names to us. The sky is blue and the grass is green. But who’s to say what each individual person (each individual pair of eyes and brain) actually perceive? While you and I both call the sky blue we could actually be perceiving two totally different things! If you borrowed my brain you could be shocked to see that what I call blue is what you’ve learned to call green! Philosophers call this color qualia. But since we’re laser physicists and not philosophers let’s move on to some experimentation!

With the aid of your green laser and some colored objects you can very easily demonstrate to yourself and others the nature of color.

Background

• Laser light is near-monochromatic (consisting of a narrow band of wavelengths) and so is of one color. A green laser produces green light (532nm wavelength).

• Color is not an intrinsic property of an object but a combination of the properties of an object and the way your eyes and brain receive and interpret sensory data. The reason that an object appears blue is that it reflects the blue wavelength only, while absorbing other wavelengths.

Purpose: to observe the nature of color with the aid of a laser.

Materials

1. <5mW green laser pointer
2. Pieces of colored paper (black, green, blue, yellow, white, red)

Safety: in this experiment a <5mW (ClassIIIa) laser pointer will be used. ClassIIIa lasers are deemed safe for momentary eye exposure. However, NEVER shine a laser into yours or anyone else’s eyes and be mindful of the laser light reflecting off of surfaces.

Procedure

1. Shine the green laser pointer at the different colors of paper.
2. Make observations. Observe visually the differences in the spot of green laser light upon the different colors of paper. You can record your observations by writing them down on a piece of paper to be reviewed later. Is the spot of laser light brighter or dimmer depending on what color of paper it is projected onto? Is the spot of laser light bigger or smaller in diameter? You can use a ruler to measure the diameter of the spot of laser light.

Observations

Review the observations you have made.

Explanation

Black Paper: the brightness of the spot of laser light is the least intense and the diameter of the spot of laser light is smallest on black paper as black absorbs all colors and reflects none.

White Paper: the brightness of the spot of laser light is the most intense and the diameter of the spot of laser light is largest on white paper as white reflects all colors and absorbs none.

Green Paper: the brightness and diameter of the spot will be similar to that of white paper as green reflects the green light of the laser pointer as does white.

Red Paper: the brightness and diameter of the spot will be similar to that of black paper as red absorbs the green light of the laser pointer as does black.

Yellow or Blue Paper: your observations of the green laser light on yellow or blue paper illustrate some of the concepts of color mixing. If you take yellow and blue paint in proportionate quantities and mix them together the resulting color of the mixture of paints will be green. This is so because both the color yellow as well as the color blue reflect wavelengths corresponding to green, as shown in the following diagram:

Conclusion

Objects are said to have a particular color based on which wavelengths of light they reflect and which wavelengths they absorb and how this information is processed by our eyes and brain.

Copyright 2007 NOVAlasers INC