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Visible Light الضوء المرئي شرح مفصل
Seeing the Light
Let's take a moment to talk about visible light. As you can tell by the name, visible light is the light that humans can see. More specifically, you see the light that is not absorbed by objects. Green plants are green because they absorb all of the colors of the visible spectrum except the green color (you could also say the green wavelengths). A red wall is red to your eyes because it is not absorbing light from the red wavelengths. Mirrors reflect all of the colors of visible light.
Not Seeing the Light
We describe the world the way we see it as humans. Other living things on Earth see the world in different ways. Dogs only see things in black, white and gray. Some insects see colors that none of us can see. When you are learning about visible light you should remember we mean visible to humans. We should also mention that not all humans can see all the colors. There is an eye defect called color-blindness that affects many men. Color-blind men cannot see certain colors of the spectrum. It has to do with a genetic defect in their eyes.
Visible Light Colors
We now introduce you to Mr. Roy G. Biv. Was he a scientist? No. Did he create great optics and telescopes? No. He is not even a he. ROY-G-BIV is the acronym that represents all of the colors in the visible spectrum of light. R (red) - O (orange) - Y (yellow) - G (green) - B (blue) - I (indigo) - V (violet). Not only are those the colors we can see as humans, but they are also in the right order. Red has the longest wavelength and violet has the shortest. You could also say that red is the least energetic and violet is the most energetic of the visible spectrum.
Edges of Visibility
Although we can't see them with our eyes, some wavelengths of light that bookend the visible spectrum are also important. Infrared radiation is next to the red portion of the spectrum. Infrared light is heat. Scientists use infrared light sensing optics when they want to see differences in temperature. Ultraviolet radiation (UV) is just beyond the violet end of the visible spectrum. UV light is given off by the Sun and absorbed by ozone in the atmosphere. Ultraviolet light can also mutate cells in your skin and give you skin cancer.
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