Discharge Bulbs

The Fluorescent Light Bulb or Tube

Fluorescent bulbs work by ionizing mercury vapor in a glass tube. A current first causes electrons in the gas to emit photons at UV frequencies. The UV light is then converted into visible light using a phosphor coating on the inside of the tube.  A wide range of colours are possible: the colour of the light depends on type and pressure of the gas, current and other variables such as the coating on the glass. This discharge principle serves bulbs, photo flashes, stroboscopes, as well as many stage spotlights. Plasma/display screens are also made up of tiny gas discharge chambers located between two glass plates. Fluorescent lights are often used in commercial sectors because of their relatively high energy efficiency.

It usually takes a few minutes for a fluorescent lamp to reach its maximum brightness - until the mercury in the lamp reacts with the phosphor coating. An electrical ballast is always needed to limit the current flow to the appropriate level and to control the gas process.

Fluorescent lamps are often referred to as "neon tubes". True neon tubes, in which neon indeed creates the light, are mercury-free, red-orange, and mainly used for neon signs. Many fluorescent lamps contain other gases such as argon, krypton or xenon, in addition to mercury.

The basic technique of gas discharge was invented at the end of the 19th century and patented in 1938 as a fluorescent tube with artificial light suitable for everyday use.

Fluorescent tubes have special versions (T2-12), with which they are used in appropriately equipped lamps. In the compact fluorescent lamps, the fluorescent tube is bent several times and provided with an E27 socket, so that it can be used in standard sockets and lights.

Compact fluorescent lamps have been manufactured since 1980 and marketed as "energy saving lamps". Because they have a very unbalanced colour spectrum, often flicker (which depends on the quality of the ballasts used) and hum, and especially due to the mercury content, energy-saving lamps have been controversial since their discovery and rather unpopular in the private sector.

Fluorescent lamps, in contrast to incandescent lamps, do not have a continuous colour spectrum. They are available - depending on the colour temperature - in different shades of white, or colours. So-called full-spectrum or daylight lamps ("true light") are based on midday light, so they have a very bright light of around 6000 Kelvin and a much better spectrum than the much cheaper standard fluorescent lamps. Compared to sunlight, however, they have a much higher proportion of blue.

The Metal-halide Bulb

Metal-halide bulbs are lamps that, as with the fluorescent tube, are also gas discharge lamps. However, the inside of the glass bulb is not coated with chemical phosphors, rather a metal-halide bulb produces light by an electric arch through a mixture of vaporized mercury and compound metals that move inside the bulb.

Metal coatings are also often used in standard household fluorescent lamps.

There is a wide range of types of metal halide lamps; they are used, for example, for curing materials, for photographic applications, cinema projectors, stage lights, solariums, disco lights, street, hallway and shop lighting. The base depends on the type of lamp.

Metal-halide and sodium vapor, high or low-pressure lights (HPS), are most commonly in outdoor and street lighting.

The oldest metal halide lamp is the mercury vapor lamp, which was invented in 1892. It first produced a blue-green light, then later crisp white light. Today mercury gas lamps have largely been replaced by metal halide lamps or LED lamps.

In addition to metals, halogen metal halide lamps also contain halogens; in contrast to the high-pressure mercury vapor lamps, they have a particularly colour-true light spectrum with the best colour rendering values.