Discharge Bulbs

All discharge bulbs use phosphors, gases, in a transparent container, that create light when excited by electrons.

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.

Technical Data
Power: 6-70 Watt, depending on size
Luminous flux: depends on the power
Luminous efficacy: depends on colour temperature, 40-100 lm/W
Energy efficiency: A (from A++ bis E, i.e. relatively high value in terms of efficiency)
Colour temperature: depends on the lamp 2700 K to 8000 K (from warm white to daylight white)
Colour rendering: 58-80 CRI (from 100, poor in terms of colour rendering)
Lifespan: approx. 6000 hours



Fluorescent bulbs are more energy efficient than thermal radiators.


Fluorescent bulbs consume unnecessary reactive power. Production, particularly the transportation routes from China to Europe, is more expensive than incandescent bulbs.

Fluorescent bulbs take time to warm up when switched on, cause a significant amount of electro smog, eye-irritating flicker and make distracting noises. Their colour rendering is poor due to the discontinuous spectrum.

All fluorescent lamps contain mercury, therefore must be disposed of as hazardous waste. If such a lamp breaks, open windows immediately to avoid being harmed by the mercury.

LED far surpass fluorescent lamps for energy efficiency, therefore fluorescent bulbs are considered less sustainable.

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.

Technical Data
Power: 20 - 24.000 watts, depending on type and usage
Luminous flux: depends on the power
Luminous efficacy: industrial, up to 117 lm / W, relatively high
Energy efficiency: not specified for special lamps, for commercial types on average A +, so very good energy efficiency
Colour temperature: depending on the lamp from 2700 K to 6000 K, with special lamps over 20.000 K (from warm white to extremely bright)
Colour rendering: 58 - 96 CRI (from 100, poor to very good) Street lights with sodium vapor lamps, the orange colour produces poor colour rendition, but very good for film and photography)
Lifespan between 6.000 and 12.000 hours, up to 30.000 hours possible, some specialized bulbs only 500 hours.



Metal-halide lamps are extremely energy efficient and perfectly suited for large and long-lasting lighting (e.g. street lighting).

Unlike LEDs, they have unbound light, so they emit light over a wide surface. They are small so can be used in compact lights and small burners, offering good light control. They are specialised lights, used in specific fields such as stage, film and photography.

Although orange streetlamps have poor colour rendition, they cause significantly less light pollution than blueish-white metal halide lights and LEDs, attract fewer insects, and emit in poor weather conditions like fog.


Metal-halide bulbs can only be used in lamps designed for these bulbs. They do not emit light immediately when turned, they take time to warm up.

The discharge vessel is under high pressure, so must be encased in a protective glass cover.

Some lamps emit high levels of UV radiation, so they are equipped with an ultraviolet absorbing glass panel.

Metal-halide bulbs are not particularly suitable for household use.