sources of visible light

luminescence

Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence. Luminescence, in turn, can occur in several different ways: One type of luminescence is called fluorescence. In this process, a substance absorbs shorter-wavelength ultraviolet light and then gives off light in the visible range of wavelengths. Certain minerals produce light in this way, including gemstones such as amethyst, diamond, and emerald. Another type of luminescence is called electroluminescence. In this process, a substance gives off light when an electric current passes through it. Gases such as neon, argon, and krypton produce light by this means. The car dash lights in the Figure 1.2 are produced by electroluminescence. A third type of luminescence is called bioluminescence. This is the production of light by living things as a result of chemical reactions. The jellyfish in the opening photo above produces light by bioluminescence. So does the firefly in the Figure 1.3. Fireflies give off visible light to attract mates.

the light we see

Visible light includes all the wavelengths of light that the human eye can detect. It allows us to see objects in the world around us. Without visible light, we would only be able to sense most objects by sound, touch, or smell. Like humans, most other organisms also depend on visible light, either directly or indirectly. Many animalsincluding predators of jellyfishuse visible light to see. Plants and certain other organisms use visible light to make food in the process of photosynthesis. Without this food, most other organisms would not be able to survive. Q: Do you think that some animals might be able to see light that isnt visible to humans? A: Some animals can see light in the infrared or ultraviolet range of wavelengths. For example, mosquitoes can see infrared light, which is emitted by warm objects. By seeing infrared light, mosquitoes can tell where the warmest, blood-rich areas of the body are located.

illumination

Many other objects appear to produce their own light, but they actually just reflect light from another source. Being lit by another source is called illumination. The moon in the Figure 1.4 is glowing so brightly that you can see shadows under the trees. It appears to glow from its own light, but its really just illuminated by light from the sun. Everything you can see that doesnt produce its own light is illuminated by light from some other source.

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incandescence

Most of the visible light on Earth comes from the sun. The sun and other stars produce light because they are so hot. They glow with light due to their extremely high temperatures. This way of producing light is called incandescence. Incandescent light bulbs also produce light in this way. When electric current passes through a wire filament inside an incandescent bulb, the wire gets so hot that it glows. Do you see the glowing filament inside the incandescent light bulb in the Figure 1.1? Q: What are some other sources of incandescent light? A: Flames also produce incandescent light. For example, burning candles, oil lamps, and bonfires produce light in this way.

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instructional diagrams

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questions

visible light includes all the wavelengths of light that the human eye can detect.

-->  a. true

b. false

some animals can see infrared or ultraviolet light.

-->  a. true

b. false

objects that produce light by incandescence include

a) candles.

b) bonfires.

c) oil lamps.

-->  d) all of the above

substances that produce light by electroluminescence include

a) diamond.

b) emerald.

-->  c) neon.

d) all of the above

diagram questions

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