Mercury-vapor lamp

Mercury-vapor lamp is a type of gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is contained in a bulb that is made of glass or quartz. Mercury-vapor lamps are more energy efficient than incandescent and most fluorescent lights, with a luminous efficacy of 35 to 65 lumens/watt. They emit a bluish-green light that is not very flattering to human skin color, but they are used in large-scale lighting applications such as street lighting, industrial lighting, and in some projectors.

History

The mercury-vapor lamp was invented in 1901 by American engineer Peter Cooper Hewitt. Hewitt's lamp was a significant improvement over the existing incandescent light bulb technology, offering higher efficiency and longer life. However, the light emitted by the original mercury-vapor lamps had a bluish-green color due to the lack of phosphor coating that could convert the ultraviolet light to a broader spectrum of visible light. This issue was addressed in the 1930s with the introduction of phosphor-coated lamps, which emitted a more pleasant white light.

Design and Operation

A mercury-vapor lamp consists of an inner arc tube made of quartz or borosilicate glass, which contains a small amount of mercury and an inert gas, typically argon, at low pressure. The arc tube is enclosed in an outer bulb that may be coated with phosphor. When electricity is applied to the electrodes at each end of the tube, it ionizes the gas and produces an electric arc that vaporizes the mercury. The vaporized mercury atoms emit ultraviolet light as they return to their ground state, which then causes the phosphor coating on the bulb to fluoresce, producing visible light.

Types

There are two main types of mercury-vapor lamps: low-pressure and high-pressure. Low-pressure mercury-vapor lamps are more efficient but emit a very narrow spectrum of light, which is primarily used in ultraviolet applications such as disinfection and photolithography. High-pressure mercury-vapor lamps, on the other hand, have a broader spectrum of light and are used for general lighting purposes.

Applications

Mercury-vapor lamps are used in a variety of applications where high-intensity, broad-spectrum light is required. They are commonly used in street lighting, parking lot lighting, gymnasiums, factories, and as grow lights in horticulture. Despite their efficiency, the use of mercury-vapor lamps has declined in favor of LED lighting, metal halide lamps, and sodium-vapor lamps, which offer better energy efficiency and color rendering.

Environmental and Health Concerns

The use of mercury in these lamps poses environmental and health risks if the lamps are broken or disposed of improperly. Mercury is a toxic heavy metal that can contaminate air, water, and soil, posing a threat to human health and the environment. As a result, many countries have implemented regulations for the disposal and recycling of mercury-containing lamps.

See Also

• Fluorescent lamp
• Gas discharge lamp
• Light pollution
• Lighting