The different lamp technologies
Artificial luminous radiation can be produced from electrical energy according to two principles: incandescence and electroluminescence.
Incandescence is the production of light via temperature elevation. The most common example is a filament heated to white state by the circulation of an electrical current. The energy supplied is transformed into heat by the Joule effect and into luminous flux.
Luminescence is the phenomenon of emission by a material of visible or almost visible luminous radiation. A gas (or vapors) subjected to an electrical discharge emits luminous radiation (Electroluminescence of gases).
Since this gas does not conduct at normal temperature and pressure, the discharge is produced by generating charged particles which permit ionization of the gas. The nature, pressure and temperature of the gas determine the light spectrum.
Photoluminescence is the luminescence of a material exposed to visible or almost visible radiation (ultraviolet, infrared).
When the substance absorbs ultraviolet radiation and emits visible radiation which stops a short time after energization, this is fluorescence.
Incandescent lamps
Incandescent lamps are historically the oldest and the most often found in common use.
They are based on the principle of a filament rendered incandescent in a vacuum or neutral atmosphere which prevents combustion.
A distinction is made between:
- Standard bulbs
These contain a tungsten filament and are filled with an inert gas (nitrogen and argon or krypton).
- Halogen bulbs
These also contain a tungsten filament, but are filled with a halogen compound and an inert gas (krypton or xenon). This halogen compound is responsible for the phenomenon of filament regeneration, which increases the service life of the lamps and avoids them blackening. It also enables a higher filament temperature and therefore greater luminosity in smaller-size bulbs.
The main disadvantage of incandescent lamps is their significant heat dissipation, resulting in poor luminous efficiency.
Fluorescent lamps
This family covers fluorescent tubes and compact fluorescent lamps. Their technology is usually known as “low-pressure mercury”.
In fluorescent tubes, an electrical discharge causes electrons to collide with ions of mercury vapor, resulting in ultraviolet radiation due to energization of the mercury atoms. The fluorescent material, which covers the inside of the tubes, then transforms this radiation into visible light.
Fluorescent tubes dissipate less heat and have a longer service life than incandescent lamps, but they do need an ignition device called a “starter” and a device to limit the current in the arc after ignition. This device called “ballast” is usually a choke placed in series with the arc.
Compact fluorescent lamps are based on the same principle as a fluorescent tube. The starter and ballast functions are provided by an electronic circuit (integrated in the lamp) which enables the use of smaller tubes folded back on themselves.
Compact fluorescent lamps (see Fig. N35) were developed to replace incandescent lamps: They offer significant energy savings (15 W against 75 W for the same level of brightness) and an increased service life.
[a]-
[b]-
Fig. N35: Compact fluorescent lamps [a] standard, [b] induction
Lamps known as “induction” type or “without electrodes” operate on the principle of ionization of the gas present in the tube by a very high frequency electromagnetic field (up to 1 GHz). Their service life can be as long as 100,000 hrs.
Discharge lamps ( see Fig. N36)
Fig. N36: Discharge lamps
The light is produced by an electrical discharge created between two electrodes within a gas in a quartz bulb. All these lamps therefore require a ballast to limit the current in the arc. A number of technologies have been developed for different applications.
Low-pressure sodium vapor lamps have the best light output, however the color rendering is very poor since they only have a monochromatic orange radiation.
High-pressure sodium vapor lamps produce a white light with an orange tinge.
In high-pressure mercury vapor lamps, the discharge is produced in a quartz or ceramic bulb at high pressure. These lamps are called “fluorescent mercury discharge lamps”. They produce a characteristically bluish white light.
Metal halide lamps are the latest technology. They produce a color with a broad color spectrum. The use of a ceramic tube offers better luminous efficiency and better color stability.
Light Emitting Diodes (LED)
The principle of light emitting diodes is the emission of light by a semi-conductor as an electrical current passes through it. LEDs are commonly found in numerous applications, but the recent development of white or blue diodes with a high light output opens new perspectives, especially for signaling (traffic lights, exit signs or emergency lighting).
LEDs are low-voltage and low-current devices, thus suitable for battery-supply. A converter is required for a line power supply.
The advantage of LEDs is their low energy consumption. As a result, they operate at a very low temperature, giving them a very long service life. Conversely, a simple diode has a weak light intensity. A high-power lighting installation therefore requires connection of a large number of units in series and parallel.
| Technology | Application | Advantages | Disadvantages |
| Standard incandescent |
- Domestic use - Localized decorative lighting |
- Direct connection without intermediate switchgear - Reasonable purchase price - Compact size - Instantaneous lighting - Good color rendering |
- Low luminous efficiency and high electricity consumption - Significant heat dissipation - Short service life |
| Halogen incandescent | - Spot lighting - Intense lighting |
- Direct connection - Instantaneous efficiency - Excellent color rendering |
- Average luminous efficiency |
| Fluorescent tube | - Shops, offices, workshops - Outdoors |
- High luminous efficiency - Average color rendering |
- Low light intensity of single unit - Sensitive to extreme temperatures |
| Compact fluorescent lamp | - Domestic use - Offices - Replacement of incandescent lamps |
- Good luminous efficiency - Good color rendering |
- High initial investment compared to incandescent lamps |
| HP mercury vapor | - Workshops, halls, hangars- Factory floors | - Good luminous efficiency - Acceptable color rendering - Compact size - Long service life |
- Lighting and relighting time of a few minutes |
|
High-pressure sodium |
- Outdoors - Large halls |
- Very good luminous efficiency | - Lighting and relighting time of a few minutes |
| Low-pressure sodium | - Outdoors - Emergency lighting |
- Good visibility in foggy weather - Economical to use |
- Long lighting time (5 min.) - Mediocre color rendering |
| Metal halide | - Large areas - Halls with high ceilings |
- Good luminous efficiency - Good color rendering - Long service life |
- Lighting and relighting time of a few minutes |
| LED | - Signaling (3-color traffic lights, “exit” signs and emergency lighting) | - Insensitive to the number of switching operations - Low energy consumption - Low temperature |
- Limited number of colors - Low brightness of single unit |
| Technology | Power (watt) | Efficiency (lumen/watt) | Service life (hours) |
| Standard incandescent | 3 – 1,000 | 10 – 15 | 1,000 – 2,000 |
| Halogen incandescent | 5 – 500 | 15 – 25 | 2,000 – 4,000 |
| Fluorescent tube | 4 – 56 | 50 – 100 | 7,500 – 24,000 |
| Compact fluorescent lamp | 5 – 40 | 50 – 80 | 10,000 – 20,000 |
| HP mercury vapor | 40 – 1,000 | 25 – 55 | 16,000 – 24,000 |
| High-pressure sodium | 35 – 1,000 | 40 – 140 | 16,000 – 24,000 |
| Low-pressure sodium | 35 – 180 | 100 – 185 | 14,000 – 18,000 |
| Metal halide | 30 – 2,000 | 50 – 115 | 6,000 – 20,000 |
| LED | 0.05 – 0.1 | 10 – 30 | 40,000 – 100,000 |
Fig. N37: Usage and technical characteristics of lighting devices
