Interior lighting not only illuminates dark rooms, creating mood and atmosphere, it emphasizes areas of importance and highlights prized possessions. But selecting the best interior lighting for both practical illumination and as a powerful decorating tool isnt automatic. You need to develop a lighting plan for each room that serves your lifestyle and complements your personal decorating style (Young). Luminance and Chrominance It is easier to take advantage of these effects when the interior is described in terms of luminance and chrominance.
Luminance is closely related to the perception of brightness, whereas chrominance is related to the perception of color hue and saturation. By definition, luminance is proportional to the light energy emitted per unit projected area of source, but the energy in each band of wavelengths of the input is scaled by the corresponding sensitivity of the eye in that band. Therefore, luminance is a measure of the physical energy of the light source reaching the eye, but the incident energy is weighted according to the spectral sensitivity of the eye (Tregenza and Loe).
The color of an object or surface is determined by its reflected or transmitted light. Color is not a physical property of the things we see it is the consequence of light waves bouncing off or passing through various objects. What is perceived as color is the result of materials reflecting or transmitting energy in particular regions of the visible spectrum. A light source that emits radiant energy comparatively balanced in all visible wavelengths appears white in color. Passing a narrow beam of the white light through a prism separates and spreads the individual wavelengths, allowing the eye to distinguish among them.
The resulting visual phenomenon is called color spectrum. White light sources emit energy at all or almost all visible wavelengths, but not always in an ideal proportion. Almost all sources are deficient at some wavelengths yet still appear to be white. This deficiency influences the perception of colors; the effect is known as color rendition. It causes the graying of some colors while enhancing the vividness of others (Gordon). Daylight A principal characteristic of daylight is its variability. The color of daylight changes with the time of day, the cleanliness of the atmosphere, and the inter reflection of surrounding objects.
The intensity of the sun changes with the time of the day, the time of year, and the latitude of the site. The luminance of the sky depends on whether the light is coming from an overcast sky, from a clear sky only, or from a clear sky and direct sunlight. Daylight has two components: sunlight and skylight. Sunlight is the directional beam emitted by the sun; skylight is the diffuse reflection of light from particles in the atmosphere (Gordon). Incandescent Lamps The incandescent lamp depends on passing an electric current through a wire to such an extent that it glows white hot.
Tungsten wire is now used, but early lamps used carbon filaments; it is necessary to have a material with a high melting point so that it emits light for reasonable length of time without breaking. The tungsten wire is usually coiled and coiled again to produce a fine filament. This is supported on two wires, which connect it to the electricity supply. The bulb usually contains an inert gas to stop the filament oxidizing; sometimes a vacuum is used. But gradually, as the lamp operates, tungsten evaporates from the filament and is deposited on the inside of the bulb.
The filament becomes thinner and eventually breaks. An inert gas filling retards this process and ensures a reasonable lamp life, typically about 1000 hours. The actual life varies within a batch of lamps, and although a mean value can be quoted this may not be helpful. Lamp manufacturers often give the life as the point when they expect a particular percentage of lamps to have failed (Tregenza and Loe). Discharge Lamps The Glowing Gas Light can be produced by an electric discharge in a gas-filled transparent tube. The discharge is started by applying a high voltage across electrodes at each end.
This ionizes the gas filling, enabling an increasing current to flow, and resulting in further ionization. The radiation produced depends in the materials in the tube ad the as pressure. Its spectrum is discontinuous, and comprises bands of radiation at specific wavelengths. Phosphor coatings in the inside wall of the tube may be used to absorb some of the radiation and re-emit it at different wavelengths especially to convert ultraviolet radiation to energy in the visible range. With all discharge lamps additional equipment is required in the electrical circuit.
This produces an initial high voltage to start the discharge, then limits the current during operation and controls the power factor. The power factor depends on the relationship between voltage and current in an ac circuit and affects the efficiency of the equipment. The combined efficacy of the lamp and its control circuit determine the energy efficiency (Tregenza and Loe). The fluorescent lamp is the most versatile package of light available in todays market. Ranging in light output from 115 lumens to 16,500 lumens in standard sizes, they are available in 40 different wattages and numerous circuit types.
Fluorescent lamps are known as gaseous discharge lamps; they produce light by discharging an electric arc through a tube filled with low-pressure gas which contains mercury atoms. Some of the electrons in the arc collide with electrons in the mercury atoms. When collisions occur the mercury electrons are knocked out of orbit and, because they have absorbed energy as a result of the collision, jump to a higher energy level. They return to their normal orbit almost immediately and, in the process, give up the energy which was absorbed (Lindsey).