Seeing Red: How Different Are the Colors of Red Laser Pointers?

Overview

Objectives/Goals I noticed that the colors of some red laser pointers were slightly different when I aimed them at a wall. However, other family members did not see any difference, so I wanted to know who was right. My experiment was to find out exactly how different the colors were by measuring the wavelength of each pointer. Methods/Materials I used 3 red laser pointers (wavelengths marked between 630 and 680nm on the label) and one green laser pointer (wavelength 532nm). The green pointer was my control. I used a diffraction grating to disperse the laser beam from each pointer onto a screen. By measuring the distance between the grating and the screen, as well as the distance between the dots of diffracted light on the screen, I calculated the wavelength of light from each laser pointer. For each pointer, I repeated the experiment with three gratings and three different distances between the grating and screen. Results The measured wavelength of the green laser pointer was withing 2 nanometers of the wavelength marked on its label. That showed that my measurements were accurate. The results for the red laser pointers showed that their average wavelengths were very close--within 7 nanometers of one another. Conclusions/Discussion At first, I thought that because the wavelengths were so close, the colors of the red laser pointers were really the same. I found out, though, that the human eye can see differences in color when the wavelengths are only 2-4 nanometers apart. Therefore, I concluded that although the wavelengths were only 7 nm apart, that difference could be seen. Because I am the youngest in my family, as a future experiment I think it would be interesting to find out if the ability to see small changes in color decreases with age.

Competition history

• CSEF 2003 Physics & Astronomy · Entry J1534

Resources

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