The choice of a suitable light bulb for a specific application is a complex process during the design phase since a variety of parameters come into play:
The supply voltage, electric power, luminous flux, luminous efficiency, durability, consumption and energy savings, color rendering index, color temperature, comfort, and miniaturization. All these parameters affect the type of activity, the project’s aesthetics, the objects you wish to highlight, and visual wellbeing; all of these factors are then coupled with an assessment of the economic and environmental impact. The following is a brief description and classification of the primary artificial light bulb types.
Light bulb types
Types of light bulbs are the following:
LEDs are increasingly used in lighting projects to replace conventional sources. From an application standpoint, LEDs are now widely used when a lighting system is required to have the following characteristics:
- saturated colors
- dynamic effects (RGB color variation)
- long life and robustness
- enhancement of shapes and volumes.
LEDs present the following advantages from a lighting standpoint:
- operating reliability
- reduced maintenance costs
- high efficiency (compared to incandescent and halogen lamps)
- clean light because it lacks IR and UV rays
- easy to manufacture efficient plastic lenses
- flexibility in installing lighting points
- saturated colors
- can provide a strong spot effect (almost point-like source)
- safe operation due to very low voltage (normally between 3 and 24V DC)
- cold-start (up to -40°C) without any problems
- insensitive to moisture and vibrations
- duration is not influenced by the number of on/off operations
A fluorescent lamp is a “gas discharge” light source. Light is produced by the stroke of an arc between tungsten electrodes, placed inside a tube containing mercury and low-pressure gas. The arc excites the mercury atoms, which generate radiant energy accordingly, mainly in the ultraviolet radiation. Stimulated in turn by this energy, the phosphor coating inside the tube emits light by converting ultraviolet radiation into visible light. Fluorescent lamps have two electrical requirements. A voltage peak must be created to turn on the lamp, triggering the arc. Once the lamp is turned on, the gas has lower resistance and the current must be limited. For this reason, as for other discharge light sources, fluorescent lamps must operate with a specifically designed power supply unit. Two different types of power supplies are used to control fluorescent lamps: magnetic or electronic type.
Both perform the same functions, but the electronic units offer specific advantages. Firstly, they are much more efficient, providing savings on energy absorbed by the system of up to 27%; moreover, they dissipate less heat and produce a stable, flicker-free light. Another important improvement introduced in fluorescent lamp technology is the development of T8 bulbs in tri-phosphor technology, thereby improving the system’s efficiency (up to 30% more luminous flux than a standard lamp of equal power).
The application segment for fluorescent technology with the highest growth rate currently lies in compact fluorescent lamps. They consist of a much thinner tube that is folded and a plastic base which, in some versions, contains a conventional power or electronic power supply. Compact fluorescent lamps are small enough to allow for the replacement of incandescent lamps in applications based on scattered light, thereby providing the benefits of increased efficiency in fluorescent technology to a wider range of luminaires.
High-intensity discharge lamps
The technology of high-intensity discharge lamps is similar to that of fluorescent lighting; an arc is generated between two electrodes inside a gas-filled tube. In this case, the operating mechanism differs from that of fluorescent lights. The electrodes (placed at the ends of a sealed discharge tube) are only a few centimeters apart, and the gas contained in the tube is at high pressure.
This allows the arc to generate extremely high temperatures, vaporizing the metallic elements contained in the gas and releasing large amounts of radiant energy in the visible spectrum. Three main types of discharge lamps exist high-intensity mercury vapor, metal halide, and sodium. The designations refer to the metallic elements present in the gas shell in which the arc is struck: the different color characteristics and the lamp’s efficiency depend on these elements.
High-intensity discharge lamps have electrical characteristics that must be satisfied by a power supply unit designed according to the type of lamp and power output.
High-intensity discharge lamps require a warm-up time to produce their nominal luminous flux: even a momentary absence of voltage requires a restart of the system and warm-up time, a process that can take several minutes.
Mercury vapor lamps
Mercury vapor is the oldest high-intensity discharge lamp technology, producing both visible and ultraviolet energy, and requiring an outer bulb capable of filtering UV radiation. In itself, a mercury vapor discharge lamp generates a bluish light with a high color temperature and low chromatic yield. A coating of phosphorus is often used to lower the color temperature and bring the chromatic yield back within acceptable limits. The use of these light sources has been significantly reduced due to technological developments that have made available other types of high-intensity discharge lamps, featuring improved efficiency and better chromatic properties.
Metal halide lamps
Metal halide lamps are the most efficient white light sources available today. They provide high efficiency, excellent color rendering, long service life, and a low luminous flux decay. These lamps make use of halides, contained in the gas in which the arc occurs, capable of producing light in areas of the spectrum that mercury vapor alone would not be able to generate. Some metal halide lamps use phosphor coatings to further improve their chromatic properties. Precisely because of their many advantages, these lamps are widely used for the illumination of internal commercial environments, particularly when very high ceilings require powerful illumination.
Today, their range also extends to small power outputs, allowing for high performance in a compact size, the ideal solution for architectural lighting applications and accent lighting. Yet another technology lies in metal halide lamps with a ceramic discharge tube, which is characterized by exceptional chromatic rendering stability and color temperature.
High-intensity, high-pressure sodium discharge technology is characterized by even higher efficiency, but with a low chromatic yield index. By adding sodium to the gases contained in the discharge tube, these lamps generate high performance in terms of luminous efficiency and extremely long service life. However, sodium lamps produce a light that is concentrated in the yellow/orange portion of the spectrum and has a poor chromatic yield.
This limits its use to external and industrial lighting applications in which the benefits of high efficiency and long life counterbalance the disadvantages of a low chromatic yield index. In high-pressure sodium lamps, the discharge tube contains both mercury vapors and sodium. Some types of high-pressure sodium lamps may replace less efficient mercury vapor lamps in a variety of applications. Low-pressure sodium lamps are a variant characterized by the emission of light in a single wavelength in the yellow portion of the spectrum. These lamps have the highest efficiency of all light sources and are used wherever high efficiency and long service life are the sole requirements.
Albeit with a number of improvements, incandescent lamps have been using the same basic technology developed over a century ago. A tungsten filament placed inside of a glass bulb is brought to incandescence by the passage of electric current. Modern lamps, however, use a filament composed of tungsten powder, which improves efficiency. In order to prevent combustion, incandescent lamps are filled with mixtures of inert gases (a vacuum was once created inside the bulb).
For a long time, incandescent lamps were the most common light sources. Because standard incandescent lamps have a very low yield, they have been and will be put out of production within the European Union, according to a timetable begun in September 2009. Tungsten halogen lamps are an improvement in incandescent technology, providing improved efficiency (by up to 20%), longer life, and a higher quality of light. In a standard incandescent lamp, the tungsten filament, which is subjected to a high temperature, tends to evaporate and deposit on the walls of the bulb, reducing the amount of light emitted. In addition, the filament becomes increasingly thin and eventually breaks.
The elements contained in the gas inside a halogen lamp allow the evaporated tungsten atoms to be deposited once again onto the filament. This phenomenon slows the deterioration of the filament, improving the consistency of the luminous flux produced and extending the life of a bulb.
Halogen lamps have a higher color temperature than standard incandescent lamps. Their light contains a greater amount of blue and less yellow and appears whiter and brighter.
Although both types of light sources have a “Ra” index of 100, the greater color temperature of halogen lamps provides a more pleasant and brighter color rendering for a wide range of colors.
Very low voltage halogen lamp systems can operate efficiently with lower power outputs than voltage network systems, allowing for a high light yield from extremely compact units. This is why, by accurately controlling the light beam, very low voltage halogen lamps are particularly suitable for accent lighting. Halogen lamps are available in many variations, in a wide range of power outputs and light beam opening angles.