artificial light

vapor light

A vapor light also produces visible light by electroluminescence The bulb contains a small amount of solid sodium or mercury as well as a mixture of neon and argon gases. When an electric current passes through the gases, it causes the solid sodium or mercury to change to a gas and emit visible light. Sodium vapor lights, like the streetlight pictured in the Figure 1.4, produce yellowish light. Mercury vapor lights produce bluish light. In addition to lighting city streets, vapor lights are used to light highways and stadiums. The bulbs are very bright and long lasting so they are a good choice for these places.

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neon light

A neon light produces visible light by electroluminescence. In this process, neon or some other gas gives off light when an electric current passes through it. Other halogen gases besides neonincluding krypton and argonalso produce light in this way. The word OPEN in the sign 1.3 is a neon light. It is a long glass tube that contains neon gas. When electricity passes through the gas, it excites electrons of neon atoms, and the electrons jump to a higher energy level. As the excited electrons return to their original energy level, they give off visible light. Neon produces red light. Other gases produce light of different colors. For example, krypton produces violet light, and argon produces blue light.

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led light

LED stands for light-emitting diode. An LED light contains a material called a semi-conductor, which gives off visible light when an electric current flows through it. LED lights are used for traffic lights (see Figure 1.5) and also indicator lights on computers, cars, and many other devices. This type of light is very reliable and durable. Q: Some light bulbs produce a lot of heat in addition to visible light, so they waste energy. Other bulbs produce much less heat, so they use energy more efficiently. Which light bulbs described above would you place in each category? A: Incandescent light bulbs, which produce light by incandescence, give off a lot of heat as well as light, so they waste energy. The other light bulbs produce light by some type of luminescence, in which light is produced without heat. These light bulbs use energy more efficiently. Which types of light bulbs do you use?

turn on the lights

If youre like most people, you dont give it a thought when you flick a switch to turn on a lightat least not until the power goes out and youre left in the dark! When you flick on a light switch, electricity normally flows through the light, and some type of light bulb converts the electrical energy to visible light. This can happen in various ways, depending on the type of light bulb. Several different types of light bulbs are described below. All of them are examples of artificial light, as opposed to natural light from the sun or other sources in nature.

fluorescent light

A fluorescent light bulb produces visible light by fluorescence. Fluorescence occurs when a substance absorbs shorter-wavelength ultraviolet light and then gives off the energy as visible light. The compact fluorescent light bulb (CFL) in the Figure 1.2 contains mercury gas that gives off ultraviolet light when electricity passes through it. The inside of the bulb is coated with a substance called phosphor. Phosphor absorbs the ultraviolet light and then gives off most of the energy as visible light.

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incandescent light

An incandescent light bulb like the one pictured in the Figure 1.1 produces visible light by incandescence. Incan- descence occurs when something gets so hot that it glows. An incandescent light bulb contains a thin wire filament made of tungsten. When electric current passes through the filament, it gets extremely hot and emits light.

instructional diagrams

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questions

how does an incandescent light bulb produce visible light?

-->  a) the bulbs filament gets so hot that it glows.

b) gas inside the bulb gives off visible light.

c) electricity excites neon electrons in the bulb.

d) two of the above

in a fluorescent light bulb, mercury gas gives off visible light.

a. true

-->  b. false

gases used in halogen lights include

a) neon.

b) argon.

c) mercury.

-->  d) two of the above

a vapor light produces light by fluorescence.

a. true

-->  b. false

diagram questions

No diagram questions associated with this lesson