LIGHTS

Incandescent bulbs:

Inside a low-oxygen glass bulb, an electric current heats a filament to a very high temperature. As soon as the bulb is connected to a suitable power source, a current flows through the filament, heating it to such a high temperature that it begins to emit light. The filament is made of the transition metal tungsten, which has a very high melting point. As tungsten is difficult to mine and work with, other materials were initially used in the early days of the incandescent lamp, such as carbon or other metals, including platinum or osmium. Lamps with a carbon filament are still produced on a modest scale, but are very inefficient.

Halogen lamps:

A halogen lamp is an incandescent lamp in which the bulb is filled with an inert gas under high pressure. A small amount of halogen (bromine or iodine) is added to this gas, from which the lamp derives its name. A halogen lamp has a higher efficiency (light output per unit of energy supplied) and a longer lifespan than a standard incandescent lamp. The vast majority of the electricity supplied to an incandescent bulb is not converted into visible light, but into invisible heat (the infrared part of the electromagnetic spectrum). The ratio between visible and invisible light is mainly determined by the temperature of the filament: the higher the temperature, the greater the proportion of visible light, and thus the higher the efficiency. Furthermore, the light becomes whiter.

Gas-discharge lamps:

A gas-discharge lamp is an artificial light source in which light is produced by passing an electric current through an ionised gas. The gases used are neon, argon, xenon and krypton, and in many cases a mixture of these noble gases. Almost always, other materials are also present in the tube, such as mercury or sodium, and for some high-pressure lamps, metal halides.

Low-pressure gas discharge lamps:

These include the classic fluorescent lamps (Tubular Lamp or Tube Luminescente), a tubular lamp widely used in homes and offices. Energy-saving lamps are also of this type. To influence the colour of the light emitted by gas discharge lamps, the inside of the discharge tube in fluorescent tubes is coated with a fluorescent layer that converts the UV radiation produced during the discharge into visible light of a specific colour. Another type of low-pressure lamp is the low-pressure sodium lamp, which is mainly used for street lighting. These lamps emit monochromatic yellow light, which is undesirable in many other applications. Of all gas-discharge lamps, they have the highest luminous efficacy (approximately 200 lumens per watt).

High-pressure gas discharge lamps:

The pressure in these lamps can range from a few tens of bar to over 100 bar. These lamps are less well known to the general public, although they are widely used, mostly in professional applications. High-pressure gas discharge lamps, in the form of metal halide lamps, are frequently used for lighting in greenhouses, stables, petrol stations, shop window displays, larger retail outlets, sports grounds and high-ceilinged industrial halls. These lamps emit almost white light and are increasingly replacing the older high-pressure mercury lamps.

The lamps in a projector are also high-pressure gas discharge lamps. The spotlights used at major events, as well as the stadium lighting in football stadiums, are almost always based on high-pressure gas discharge. The headlights of modern cars are also often high-pressure gas discharge lamps; these are recognisable by their bluish light (xenon lamps). High-pressure sodium lamps are often used for street lighting. These emit a somewhat orange-yellowish light, but the colour rendering of these lamps is much better than that of low-pressure sodium lamps. Older high-pressure mercury lamps, which emit white light, are also still used for street lighting.

Whereas the temperature of the gas in a low-pressure lamp is limited to just a few tens of degrees Celsius, the gas in a high-pressure gas discharge lamp can reach temperatures of over 1000 °C. This high temperature allows for the presence of other ions in the gas through the addition of (sometimes several) salts, mercury and/or bromine. In many cases, the salts will be bromides or iodides, as this has a positive effect on the lamp’s lifespan. The metal in the salt then produces a specific spectrum and light colour. This makes the composition of these salts very important in order to achieve the most accurate colour rendering possible.