The quality of the light
The quality of light
The above process produces a clear picture of the light sources required to achieve the desired effects. We can thus leaf through catalogues having a better idea in mind of what we need, and only focus on the most appropriate appliances. We can find that an appropriate appliance is available in different versions, using different light sources, or energy supply controls.
But how do we make a decision now?
We need to be familiar with the main characteristics of the light sources (the lamps) and emission controls.
Every light source has four basic features that are relevant for the purposes of the project. Two of these influence the aesthetic characteristic of the system, while two are of an economic character. Both groups include, respectively, colour temperature, colour rendering index, luminous efficiency, and durability (or average life). While the former produce a more or less "warm" light and have a varying impact on colour perception, the latter influence energy consumption and running costs (including the cost for source replacement).
These four features differ in each lamp; likewise incandescent lamps (by now obsolete), incandescent halogen lamps, fluorescent and metallic iodide lamps, and LEDs show major differences, also in their physical appearance. Practically speaking, small-sized sources (e.g. halogen lamps) are best suited for projectors and whenever light needs to cover a long distance (4-5 metres or more from the source) and to clearly outline the illuminated area, creating light and shade, or to achieve the warm, brilliant atmosphere, typical of these lamps. Fluorescent lamps help achieve different hues of light, from warm pink to cold blue, and are suited for general illumination, for soft diffused light, or to minimize consumption. Metal iodide lamps are comparable to fluorescent lamps in terms of efficiency and, like these, allow to choose among three different colour temperatures and, therefore, to obtain warmer or colder light hues; they also provide some of the characteristics of halogen lamps, i.e., they are suited for projectors to obtain narrow and sharply defined light beams.
LED appliances in constant evolution provide benefits in terms of limited size and opportunity to change both the light intensity and the colour, ensure high efficiency, and have an extremely long life, unlike traditional ones.
Incandescent lamps are traditional lamps with Edison E27/E14 screw lamp holders. More than a century after their invention, they are now being dismissed due to their high inefficiency, close to 10 lumens/Watt.
Their nominal life is about 1000 hours, and they are sensitive to impacts and vibrations. When lit they quickly reach a temperature of up to 600° C and should not be touched with fingers or easily inflammable objects. The colour of their light is a 2700 K warm white; they enhance red hues, but fade blue nuances. They are simply powered by connecting them to the power mains.
Incandescent lamps with halogens
Halogen lamps are made to withstand higher temperatures than normal incandescent lamps; moreover the bulb contains an element (halogen) that prevents blackening of the same. Such halogen lamps are smaller than common incandescent lamps with the same power, but ensure more efficiency and a longer average life.
Some of the most popular types have a built-in reflector, which allows to direct the light flow. The appropriate light cone width and power can be chosen from a catalogue. Linear and simple bulb types of lamps can be connected to the power system, while the more common lamps with projector require a 12V energy supply and consequently a 240V/12V transformer.
Compact fluorescent lamps, also known as "energy saving lamps" are part of the family of fluorescent lamps, and were recently improved in terms of light hue and colour rendering. The use of fluorescent lamps for home illumination is therefore recommended not just because of their luminous efficiency and long life, but also for their versatility.
Fluorescent lamps require a special electronic energy supply circuit that removes the stroboscopic effect, increases the lamp's efficiency and average life, and allows prompt switching, crucial in a house.
Metal halide lamps
Metal halide lamps are almost as cheap to use and as durable as fluorescent lamps, but are also much more compact and have almost the same size as halogen lamps. They are suited to produce direct and indirect illumination, with close flow concentration achieved without consuming undue amounts of energy. They require a complex power supply system. Their main drawback is that they switch on gradually (reaching maximum performance in about 5 minutes) and above all, they are slow to restart. If accidentally switched off, peak performance is only reached about 10 minutes after restarting. They are generally not too popular for home applications due to their long start/restart time and to the heat they produce.
A Light Emitting Diode (LED) is an electronic unit that generates a particular colour of light when energy runs across it. White light is obtained using a technology similar to fluorescent tubes. Phosphor is added to a blue LED: the light of phosphor and the light of the blue LED are blended together to generate white light with different colour temperatures.
The efficiency of LEDs is by now comparable to discharge lamps. They ensure high colour rendering (technology is constantly improving in this respect) and a broad range of colours and colour temperatures. Their average life is much longer compared to all traditional lamps, they have a very limited size, but require heatsinks and power and control systems that can also be operated remotely.
The main drawback of LEDs is that they are still quite expensive.
Different types of appliances
Appliances can be distinguished, in the first place, on the basis of their fitting style: ceiling, suspension, wall, floor, table, recessed, fixed to track, or special emergency solutions.
Floor lights are the easiest solution to illuminate any room. They can be placed a few metres away from the power socket, except for the discomfort produced by the exposed cable. They are easy to move around, thus ensuring flexible illumination. Their positioning requires special care (to prevent knocks and ensure a safe distance from inflammable objects).
The main feature of lights fixed to vertical walls is that they provide diffused illumination in the room. Their light softens any shadows produced by ceiling or suspension lamps. Wall lamps can be essential to illuminate vertical surfaces, such as the walls of the room, bookcases, or paintings. Much of the lighting image of a room is often due to the use of this kind of appliances. Their luminous effects on the walls are also used for decorative purposes; however, as wall lamps require masonry work to lay the electric cables, their final position needs to be chosen carefully.
The lamp par excellence is optimal for all work done within a limited area. Combined with appropriate diffused general illumination, it is the ideal source for writing, drawing, and reading, particularly when the book is placed on a table.
Ceiling lights are fixed directly to the ceiling; therefore the maximum range of their light emission is 180 degrees. They require appropriate concealed electric cables, which may imply masonry work, except in cellars or store-rooms, where the ducts can be visible.
Lights hanging on the ceiling with wires or rigid shafts offer a broad variety of solutions. Being suspended, they provide diffused light.
False ceilings are often installed in residential interiors to lower the height and conceal cables and ducts of multiple light sources. Recessed lights are simple and, as such, cheap. However when choosing this type of lamp one must consider the material of the false ceiling and the energy that can be absorbed.
Recessed lights can also be wall mounted; in this case they are ideal to create scenic lighting effects.
Mandatory for illumination of all public areas, these lamps should also be a regular feature in every home. Emergency lights have a battery and a circuit for automated start in case of blackout. They are very useful in case of temporary power supply failure, and should be placed at the crucial points of the house: in bedrooms, near the mains switch, in the bathroom, and in the work rooms.
Lamps are not only divided according to their fitting style floor, wall, ceiling, or suspension. Every lamp is characterized by a type of emission:
Direct emission: downwards
Indirect emission: upwards
Dual emission: upwards and downwards
Wall washer emission
The choice of which light emission to use is crucial to obtain the desired ambiance. Appliances producing indirect and diffused light are not suited to create intimate and cosy ambiances; on the other hand, the sole use of projectors concentrating light on limited areas does not allow to obtain a bright, radiant interior.
The location of light sources is decisive for the quality of the lighting system. The main challenge encountered when planning home illumination often lies in the possibility, or impossibility, to place the appliances in a specific place. Walls occupied by furniture, untouchable ceilings make it hard to decide where power cables can be fitted and which positions allow to obtain the desired luminous effects.
Direction is crucial when using concentrated light appliances, as well as lamps producing diffused light, albeit for different reasons. In both cases, it is equally important to control the direction in which the light rays issue from the lamp and strike the different surfaces. Luminous effects, reflections, uncomfortable glare, and shadows are the result of careful control of this issue, which is often underestimated.