Mercury-vapor lamp facts for kids
A mercury-vapor lamp is a special type of lamp that creates light using a spark. This spark happens inside a tube filled with mercury gas. When the spark passes through the mercury, it makes the mercury atoms glow. They release both ultraviolet (UV) light and light that we can see. Some of these lamps use special coatings called phosphors. These phosphors change the invisible UV light into visible white light, making the lamp brighter and giving it a different color.
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How Mercury Lamps Light Up
Mercury-vapor lamps work by sending electricity through a small amount of mercury gas. This creates an electric spark. The spark excites the mercury atoms. When these atoms get excited, they release energy as light. Some of this light is ultraviolet, which we cannot see. Other parts are visible light.
Many mercury lamps have a special coating inside the glass bulb. This coating is made of phosphors. When the invisible ultraviolet light hits the phosphor, it changes into visible white light. This helps the lamp produce a brighter, more natural-looking light. Not all mercury-vapor lamps use these phosphor coatings, though.
What Color Light Do They Make?
The color of light from a mercury-vapor lamp can be different. It depends on how old the bulb is, its quality, and what chemicals are added to the mercury. The light can look blue-white, green-white, or almost pure white. If a lamp has a green tint, it usually means it is an older bulb. However, this does not always mean the bulb is about to stop working.
You might have seen these lamps as the bluish streetlights in your town. They are known for their distinct blue-white glow.
Why Some Are Being Replaced
The EU wants to stop using mercury-vapor lamps. This is because they contain a lot of mercury, which can be harmful to the environment. Also, newer lights like fluorescent bulbs are more energy-efficient. This means they use less electricity to make the same amount of light.
Even though mercury-vapor lamps are not as efficient, they do last a very long time. This was one of their main advantages for many years.
Improved Lamps: Metal Halide
The metal halide lamp is a newer and better version of the mercury-vapor lamp. It works in a similar way but has extra chemicals inside. Besides mercury, it also contains a metal halide, usually sodium iodide.
The metal halide adds orange light to the blue-white light from the mercury. When these colors mix, they create a very pure white light. This makes metal halide lamps great for places where clear, bright white light is needed.
Related pages
Images for kids
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A 175-watt mercury-vapor light approximately 15 seconds after starting.
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A closeup of a 175-W mercury vapor lamp. The small diagonal cylinder at the bottom of the arc tube is a resistor which supplies current to the starter electrode.
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Cooper Hewitt lamp, 1903
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Production of high-pressure mercury vapor lamps, 1965
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Mercury vapor street light
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Closeup after dark
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Example of a phosphor-coated 125 W lamp
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Line spectrum of mercury vapor. The blue-green tint of mercury vapor lamps is caused by the strong violet and green lines.
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Low-pressure Hg lamps can be rather small, but efficient sources of deep UV light.
See also
In Spanish: Lámpara de vapor de mercurio para niños
