Ward's World Activity Guides

Ward's World+McGraw Hill - Color

View, download, and print free resources for your science classroom.

Issue link: https://wardsworld.wardsci.com/i/1300813

Contents of this Issue


Page 1 of 3

Color (continued) + ward ' s science the invisible band of electromagnetic frequencies immedi- ately adjacent to and less energetic than red light is known as infrared radiation, while the invisible band more energetic than violet light is called ultraviolet. Receptors The human eye is sensitive to the wavelength, or color, of light because there are three different receptors—known as cones— in the eye that respond to three different ranges of wave- lengths, as illustrated in Fig. 3. The red (L) cones respond to light of longer wavelengths (roughly 500–700 nm). The green (M) cones respond to light of medium wavelengths (roughly 450–650 nm). The blue (S) cones respond to light of shorter wavelengths (roughly 400–500 nm). The central wavelengths for these three different ranges represent the three additive pri- mary colors: red, green, and blue. The response of these three receptors is used by the human brain to determine the color of an object. If light of a single well-defined wavelength enters the human eye, then the degree to which it stimulates the red, green, or blue receptors determines which color the observer perceives. If only the red receptors (cones) are stimulated, then the brain perceives red light. Similarly, if predominantly green recep- tors are stimulated, then the brain perceives green. However, if light at a single wavelength stimulates both the green and red receptors, then the brain perceives yellow, which lies between red and green in wavelength as shown in Fig. 3. While both re- ceptors can be stimulated by light of a single wavelength, they can also be stimulated in the same way with separate sources of light at different wavelengths. Because a single wavelength of yellow light and two wavelengths of green and red light can produce the same visual stimulus within the brain, the brain perceives the same yellow color in both cases. This is how primary colors can be mixed to make any color in the rainbow and is the basis of color displays in televisions, cell phones, and computer screens, for instance. Within each pixel of the display device, there are three different emitters for each of the three primary colors (red, green, and blue). The brightness of each emitter can be independently adjusted to stimulate an arbitrary response in the eye of the viewer for each pixel—thus, Fig. 2: Extensive chemical weathering can remove essential minerals and elements from soil. Typically, only the most insoluble compounds remain in the soil. For example, iron oxides may persist, imparting a reddish-brown color to the soil. (Credit: Stephen Reynolds)

Articles in this issue

Links on this page

Archives of this issue

view archives of Ward's World Activity Guides - Ward's World+McGraw Hill - Color