TUNGSTEN HALOGEN LIGHT SOURCE

Tungsten Halogen Light Source in the Entertainment industry

Tungsten Halogen Light Source In The Entertainment Industry

Introduction

In recent years, a great deal of effort has been devoted to solving the seriously environmental pollution problems. Compared with conventional oxidation processes, oxide semiconductor photocatalysis has several obvious advantages, such as complete mineralization of the pollutants, application of the near-UV or solar light, no addition of other chemicals, operation at near room temperature and low cost. Among various oxide semiconductor photocatalysts, TiO2 is most widely used because of its biological and chemical inertness, strong oxidizing power, nontoxicity and long- stability against photo and chemical corrosion. However, TiO2 can be only activated under ultraviolet irradiation (? < 380 nm) due to its large band gap (3.2 eV). Usually, sunlight contains about 4% ultraviolet light. So, it is of great interest to develop new visible-light photocatalysts to extend their photocatalytic applications from ultraviolet to visible-light range (Leonard Charlton 2002 286).

History

Despite deep market penetration by compact fluorescent lamps (CFL), incandescent lamps remain for the moment the most common source of electric lighting. They are to be phased out after a century of market dominance in a change driven by the commonly agreed need to cut power consumption. However, CFLs themselves are likely to be eclipsed in short order by new LED (light emitting diode) lamps, which use even less energy.

Nevertheless, incandescent lamps will definitely find a role in some specialised applications even though they are being phased out as an everyday household item.

Solids and gases emit visible light when heated to a high enough temperature. A light bulb consists of a tungsten filament positioned inside a glass bulb filled by a mixture of inert gases. Electric current flows through the filament when the lamp is turned on. The electrons which make up electric current carry energy and collide with the tungsten atoms which gain kinetic energy. As a result the tungsten atoms get hotter and the tungsten filament glows. The temperature of the filament rises to about 2500°C.

Tungsten, because of its very high melting point (3410°C) can withstand such high operating temperatures. Tungsten is a well known high-temperature refractory metal, and because it retains its hardness at high temperatures and has a high melting point, elemental tungsten is an ideal choice for high-temperature applications, such as light bulbs, cathode-ray tubes, vacuum tube filaments, heating elements and rocket engine nozzles (Price Ehrnford Andreou and Felix 2003 193). The electrical conductivity of tungsten is a third of that of copper. All these characteristics make tungsten the ideal choice for this application.

Tungsten is obtained in the form of powder, which is sintered and shaped into feedstock to manufacture the incandescent lamp filaments. The filament in its final form is a piece of thin coiled tungsten wire. The one major drawback of tungsten is its brittle nature, which makes it very difficult for making tungsten wires.

During extrusion, the filament is cold worked and residual stress from the operation can lead to recrystallisation of the filament when heated above the ...