1. The importance of light
Humans have an extraordinary ability to adapt to their environment. Light is very important because it is an essential element of our ability to understand our environment since most of the information we receive through the senses is obtained through sight.
Light is the electromagnetic phenomenon through which we can perceive radiation that is sensitive to the human eye. The electromagnetic radiation of light is of wavelength between 380 and 750 nm.
There are many ways to create light, but two of the most commonly used methods are as follows:
- Thermo-radiation is the lighting obtained when solid or liquid materials heated to temperatures above 1000 K emit visible radiation (incandescence). Filament lamps are based on this concept of generating light.
- Electrical discharge is another technique used to obtain light. When an electric current passes through a gas it emits radiation (luminescence).
When we talk about lighting systems, we refer to the systems used to provide light.
2. The lamps
A lamp or bulb is an energy converter, whose main function is to transform electrical energy into light. There is currently a wide variety of lamps on the market, with different characteristics and functions.
Different parameters define the characteristics of a lamp.
- Lumen (lm): Unit that measures the amount of light emitted.
- Color rendering (CRI): The colors we see depend on the chromatic characteristics of the light source. Thus, the CRI indicates the capacity of an artificial light source to reproduce colors, the reference (100%) being the Sun.
- Useful life: It is the estimated time in hours after which it is preferable to replace the lamps of an installation to avoid an excessive decrease in the illumination levels.
- Efficiency or luminous efficacy: Quantity of light emitted (lm) per unit of electrical power consumed (W).
Evolution of electric lamps
Although technological progress has made it possible to produce different types of lamps, the main factors influencing their development have been forces external to the market.
However, it was undoubtedly the large-scale generation and distribution of electricity that determined the growth of the market. After World War II, the fluorescent lamp became the dominant light source, and years later, in the 1970s, their design was perfected to reduce power consumption without losing the quality of light they produced.
Types of electric lamps
Incandescent lamps
Incandescent lamps are made up of a tungsten (Wolfram) filament that is heated by the Joule effect achieving such high temperatures that they begin to emit visible light.
To prevent the filament from burning (in contact with air that would oxidize it) it is wrapped in a glass bottle that is filled with a gas to prevent the filament from evaporating and leaving the globe black.
In general, the efficiency of this type of lamp is low because most of the energy consumed is converted into heat.
Types of incandescent lamps
Today, vacuum lamps are hardly used at all. Over time, blackening of the bottle can occur due to evaporation of the tungsten particles that form the filament.
- Halogen lamps: Contain a small amount of gas (CH 2Br 2), which creates a halogen regeneration cycle that prevents blackening.
The operation of these lamps requires very high temperatures for the halogen cycle to occur. For this reason, they are smaller and more compact than non-halogen lamps, and the bottles are made of quartz glass, which is more resistant to high temperatures.
They have a life of 1,500h, an efficiency of approximately 20 lm/W and a CRI also very close to 100%.
Discharge lamps
Discharge lamps are an alternative way of producing light more efficiently and economically than incandescent lamps.
In this case, light is obtained by establishing an electric current between two electrodes located in a gas-filled tube, with a potential difference between the electrodes that causes the electrical discharges necessary to obtain light.
For these lamps to work properly, it is necessary, in most cases, to have some external elements: the starters.
The starters are devices that supply a little voltage between the electrodes of the tube. This voltage is necessary to initiate the discharge and thus overcome the initial resistance of the gas to the electric current.
Other devices serve to limit the current passing through the lamp and thus avoid an excess of electrons circulating through the gas, which would increase the electrical intensity until the lamp is destroyed.
Types of discharge lamps
Discharge lamps can be classified according to the gas used or the gas pressure.
The properties vary greatly from one to another, so each lamp has a specific application.
Low-pressure mercury vapor lamps:
- Fluorescent lamps. They have no outer bottle and consist of a cylindrical tube closed at each end where the electrodes are located.
The discharge tube is filled with low-pressure mercury vapor and a small amount of gas to facilitate ignition and control the discharge of the electrodes.
The life of these lamps is between 5,000 and 10,000 hours. The color rendering of these lamps is approximately 70%.
- Compact fluorescent lamps have built-in ancillary elements to facilitate ignition and limit current. They are small lamps, designed to replace incandescent lamps with an energy saving that can reach 70% and with very good performance (between 70 lm/W and a CRI that can reach 90%).
High-pressure mercury vapor lamps:
- High-pressure mercury vapor lamps. When the mercury pressure inside the discharge tube is increased, the ultraviolet radiation characteristic of low-pressure lamps becomes less important for emissions in the visible zone. Under these conditions the light emitted is blue-green. To solve this problem, fluorescent substances are usually added to improve the chromatic characteristics of the lamp. The service life of this type of lamp is about 8,000 hours.
- Mixed light lamps. These are a mixture of a high-pressure mercury lamp with an incandescent lamp and usually have a phosphorescent coating. The result of this mixture is that it provides good color rendering. Their lifetime is limited by the life of the filament, which is the main cause of failure. In general, their average life is around 6,000 hours.
- Metal halide lamps. If metal iodides are added to the discharge tubes, a better color rendering capability of mercury vapor lamps is achieved.
The average life of these lamps is close to 10,000 hours. They need 10 minutes to ignite, which is the time required for the discharge to stabilize. Because of their operation, a special ignition device is necessary, since the voltages they require at start-up are very high. Their good chromatic characteristics make them suitable for the illumination of sports facilities, TV broadcasting, film studios, etc.
Sodium vapor lamps:
- Low-pressure sodium vapor lamps. Electrical discharge in a low-pressure sodium vapor tube produces a characteristic monochromatic radiation.
The discharge tube is U-shaped to reduce heat losses and the size of the lamp. The tubes are made of very resistant materials because sodium is very corrosive and are closed in a bottle in which the vacuum has been made to increase thermal insulation.
These lamps offer visual comfort and a good perception of contrasts. However, the fact that they are monochromatic means that color rendering is poor.
The average life of these lamps is very long, about 15,000 hours, and their service life is between 6,000 and 8,000 hours. They are commonly used for street lighting, but also for decorative purposes.
- High-pressure sodium vapor lamps. They provide a golden white light, much more pleasant than that provided by low-pressure lamps, and have better color rendering capabilities.
The average life of these lamps is 20,000 hours and their service life is between 8,000 and 12,000 hours.
The operating conditions are very demanding, as they require different temperatures.
Inside there is a mixture of sodium and mercury vapor, to dampen the discharge, which serves to facilitate lamp ignition and reduce thermal losses.
The tube is inside a bottle where the vacuum has been made.
This type of lamp has many applications, both in indoor and outdoor lighting. It is commonly used in the lighting of industrial buildings, in public lighting or in decorative lighting.
White light LEDs
White light LED lamps are one of the newest developments in lighting. They are very well positioned to be able to replace current light bulbs.
They are a semiconductor device that emits light when polarized and passed through by electric current.
The use of lamps based on LED technology is increasing significantly lately since it has a longer life than any other type of lamp, a lower fragility, and a higher energy efficiency.
Some more specific features of this lighting system are:
- Its efficiency is superior to other lamps: 100-150 lm/W.
- Its useful life is between 50,000 and 100,000 hours.
- Their CRI is approximately 90%.
- They achieve high reliability.
- They have a very fast response.
- They carry less risk to the environment.
- It is the most expensive technology.
Although they are quite expensive, they are expected to evolve rapidly. Proof of this is that manufacturers are increasingly turning to LED-based products for indoor and outdoor lighting, such as street and parking lot lighting.