Facts on lighting
Lighting has a great significance to the well-being, health and safety of human beings. This is why it also is an important element in building and interior decoration. Relying on light also gives excellent opportunities of varying the mood of a room.
What is light?
Light is electromagnetic radiation, which is invisible to the eye. Light becomes visible when it meets a surface. Colours are formed by waves of different lengths. All colours together combine to produce white light. When a ray of light is refracted in a prism or a drop of water, the whole colour spectrum of light becomes visible, such as a rainbow. The human eye is sensitive to the range of the so-called visible light, which is 380 nm - 780 nm, the extreme ends of the scale being ultraviolet (UV) and infra-red (ir) light.
The human eye is well able to adjust to the great variations in luminous strength occurring in the nature, such as the light of the moon (1 lux) and bright sunshine (100,000 lux). In artificial lighting, we usually have to be contented with minor variations, such as general lighting around 1-2,000 lux and working light 200-2,000 lux (the recommendation for office lighting is a minimum of 500 lux).
Vision
Vision is based on light; the eye is inquisitive and turns to light in order to see. Some 80% of all information is received through the eye. It is thus justified to say that light always has a story to tell. When we step into a room, our eyes circle it guided by light, and the light tells us the story of the room: its shapes, colours, architecture, decoration, ornaments etc. In good lighting, seeing is easy and pleasant - it is a treat for the eyes. (see section on light and well-being)
Decorating with light
When artificial lighting started becoming wide-spread, the room was usually equipped with one lighting fixture in the middle of the ceiling. This, however, rarely is the best way of lighting a room. Illuminated this way, the room appears smaller, as all light is concentrated in the middle, and the wall surfaces receive little of it. As light naturally attracts people, all activities thus, also become concentrated in the middle of the room. This is why it is better to divide the light over several areas determined by the functions of the room. It is also important to light the peripheral surfaces to enhance the atmosphere of the room.
Illuminating its various details also enriches the room. Optimal lighting requires several fixtures, and their lighting capacities often prove more important than their looks. Beautiful lighting fixtures will always play an important part in illumination, but the share of fixtures integrated in technical structures will increase, as the light and lighting are a central factor in creating the mood of the room. A good lighting solution also makes it possible to create different moods. This can be achieved by adjusting the lighting or selecting the correct fixtures. For example, the room can be lit with lighting fixtures of a generalised type: a standard or table lamp with a shade, a ceiling fixture with diffused radiation, a wall fixture etc.
This kind of lighting could be described as gentle, soft, friendly, almost shadow-free (as on a cloudy day).
On the other hand, the room can be lit by spotlight-type fixtures; directional spotlights, a ceiling fixture that gives limited light over a table, and downlight solutions.
In this case, the end result can be described as harsh, interesting, fascinating, but also aggressive and glary with sharp shadows (a sunny day).
In the same room, different lighting fixtures can be used to create the desirable mood. When testing people's preferences, opinions for such as the above examples, are divided almost equally, with the second alternative, however, being slightly more popular. It is believed that this is because the first impression when entering the room is stronger and more interesting. A room decorated with light surfaces is easier to illuminate, and a well-lit impression can be created with less light than in a dark room. In case the surfaces are dark, lighting fixtures of the general type do not work well, and it is easier to get good results with spotlights. In a dark room, glare is often also a problem, as the eye adjusted to dark surfaces meets a bright light.
Light quality
In the point of view of seeing, the qualitative properties of light often are more important than the quantitative ones. Qualitative properties of light: no glare - direct glare - indirect glare = lustre
good colour repetition - shiny contrast - correct colour temperature - flicker-free light
Glare
As to glare, we can talk about good and bad luxes. When driving, for example, the lights of the car are "good luxes" which help us to see, whereas the lights of the car we meet on the road are "bad luxes" which stop us from seeing (glare). The glare is not directly dependent on the amount of light, but the contrast between surfaces, such as a bright light on a dark surface. Indirect glare occurs when the light comes from the wrong direction. For example, reading a glossy magazine may become impossible without turning it towards the direction of the light.
Good colour rendering
The colour rendering capacity of light is indicated by the Ra index. Glow bulbs, including halogen bulbs, have a Ra index of 100. The spectrum of a bulb is the same as that of sunlight. The colour rendering capacities of fluorescent tubes vary according to their quality. The Ra index of high-quality fluorescent tube light sources is 90. Of discharge lamps, the best one is the multi-metal lamp, the Ra index of which is over 80. Good colour rendering properties are important when illuminating such as people, colourful art etc.
Colour temperature
The colour temperature is expressed in Kelvin (K).
In the nature, the colour temperature varies at different times of the day: The red skies in the morning and evening can be extremely warm in tone, for example 2,500 K, whereas the bluish mid-day sky can be very cold, such as 8,000 K. In home lighting, light sources with a warm tone of 2,700 - 3,000 K are generally used. In workplaces, slightly colder tones of 3,000 - 4,000 K are used.
Examples of the colour temperature: a standard glow bulb about 2,700 K, a halogen light about 3,000 K, fluorescent tubes 2,700-8,800 K.
The correct selection of the colour temperature has a significant effect on the mood of the room. If, for example, several light sources with different colour temperatures are on in the room at the same time, the general impression is incoherent. In low luminous intensities, warm tones are used, and in high ones colder tones - simulating the nature.
