Presentation on theme: "7 Artificial Lighting The subject of this chapter is artificial lighting, and the following chapter deals with natural lighting. Although the principles."— Presentation transcript:
7 Artificial Lighting The subject of this chapter is artificial lighting, and the following chapter deals with natural lighting. Although the principles of these two topics are treated separately it is important that they are considered together when designing a building.
The main functions of artificial lighting? to provide enough light for people to carry out a particular activity
to provide enough light for people to move about with ease and safety
to display the features of the building in a manner suitable for its character and purpose
To achieve these aims it is necessary to consider the properties of lamps, of the lamp fittings and of the room surfaces that surround them.
7.1 Lamps 7.1 Lamps What is The oldest source of artificial light ? the flame from fires, from candles and from oil lamps Convert chemical combustion to light energy
Modern sources of artificial light convert electrical energy to light energy produce light by heating substances to a temperature at which they glow and are luminous. (1) Incandescent sources (1) Incandescent sources (2) gas discharge sources (2) gas discharge sources produce light by passing an electric current through a gas or vapour that has become ionised and hence able to conduct electricity. At low pressure, a luminous arc or discharge is formed between the electrodes and useful quantities of light are given off
7.1.1 how to evaluate the Properties of lamps 1) Luminous efficacy 1) Luminous efficacy which is given by the following formula. Unit: lumens /watt (lm/W)
2) Life 2) Life The luminous efficacy of a lamp decreases with time and for a discharge lamp it may fall by as much as 50% before the lamp fails. The nominal life of a lamp is usually determined by the manufacturer by considering the failure rate of a particular model of lamp combined with its fall in light output. In a large installation it is desirable that all the lamps are replaced at the same time on a specified maintenance schedule.
3) The correlated colour temperature (CCT) 3) The correlated colour temperature (CCT) is the absolute temperature of a perfect radiator when the colour apperance of the radiator best matches that of the light source Unit : kelvin (K) The CCT reflects the apparent color of light itself,
The lower values of colour temperature indicate light with a higher red content.
Some examples of colour temperatures are given below Clear sky 12,000-24,000K Clear sky 12,000-24,000K Overcast sky 5,000-8,000K Overcast sky 5,000-8,000K Tubular fluorescent lamps 3,000-6,500K Tubular fluorescent lamps 3,000-6,500K Tungsten filament lamps 2,700-3,100K Tungsten filament lamps 2,700-3,100K
Which one have the better color? Which one have the better color? 4 Colour rendering 4 Colour rendering is the ability of a light source to reveal the colour appearance of surfaces. This ability is measured by comparing the appearance of objects under the light source with their appearance under reference source such as daylight One system specifies the colour rendering of lamps by a colour rendering index R a ) which has a value of 100 for an ideal lamp. Practical sources of white light range in R a value between 50and 90
To make a comparison of the colour rendering qualities of light sources easier, colour rendering groups have been defined: The CIE colour rendering groups GroupRaRa ImportanceTypical application 1A 90... 100 accurate colour matching Galleries, medical examinations, colour mixing 1B 80... 90 accurate colour judgementHome, hotels, offices, schools 2 60... 80 moderate colour renderingIndustry, offices, schools 3 40... 60 accurate colour rendering is of little importance Industry, sports halls 4 20... 40 accurate colour rendering is of no importance Traffic lighting
Some tasks such as colour matching in the printing industry have high demands in accurate colour rendering and require special attention from the lighting designer. For normal offices, however, the colour rendering group will be 1B or 2, which is easily achived with normal fluoresent lamps.
Colour rendering index for different light sources Light sourceColour rendering group Incandescent1A Metal halide1A... 2 Fluorescent1A... 3 High pressure sodium1B... 4 Low pressure sodium4
7.1.2 the fist type of artificial light Incandescent lamps 7.1.2 the fist type of artificial light Incandescent lamps Electric incandescent lamps work by passing an electric current through a filament of metal and raising the temperature to white heat. When the metal is incandescent, at around 2800K, useful quantities of light are given off.
1)Most General Incandescent lamps is tungsten filament lamp. GLS lamps, or common light bulb, has a coiled filament contained within a envelope of glass which may be clear or frosted.
The cost of a tungsten filament lamp is low and its installation is simple, but the relatively short life of the lamp can cause the labour costs of replacement to be high. The low luminous efficacy of the lamp produces high electrical running costs. Only about 5% of the electrical energy is converted to visible light and most of the energy consumed is given off as heat, especially radiant heat.
2) The improved incandescent lamps: Reflecting lamps 2) The improved incandescent lamps: Reflecting lamps The relatively large size of the standard tungsten filament lamp makes it difficult to control the direction of the light. Spot lamps are filament lamps with the glass bulb silvered inside and shaped to form a parabola with the filament at the focus. This arrangement gives a directional beam of light which is available in different widths of beam.
Crown-silvered lamps are standard filament lamps where the glass bulb is silvered in front. When this lamp is used with a special external reflector it also gives narrow beams of light
some other improved incandescent lamp 3) Tungsten-halogen lamps some other improved incandescent lamp 3) Tungsten-halogen lamps Tungsten –halogen lamps have filaments which run at higher temperatures with the presence of a small quantity of a halogen gas, such as iodine or bromine.
4) Low-voltage system uses 12volt lamps fed from the mains by a transformer. low-voltage bulbs need a lower resistance,so the filament can be shorter, thicker and stronger. The small size of these lamps give them good directional qualities which make them popular in shops for the display of goods. The relatively low heat output of low-voltage systems is also an important property in stores where high levels of illumination can cause overheating.
7.1.3 the second type of artificial light gas discharge sources Most General gas discharge source is Tubular fluorescent lamps Most General gas discharge source is Tubular fluorescent lamps
A improved form is Compact fluorescent lamps A improved form is Compact fluorescent lamps Compact fluorescent lamps give a light quality suitable for domestic purpose and the use of such lamps are important technique for low-energy lighting in homes.
How is the coulur quality of gas discharge lamps? Apart from the well-known tubular fluorescent lamp, gas discharge lamps usually have a poor colour rendering So they have in the past been restricted to outdoor lighting, such as for roadways, where their generally poor colour qualities have not been important.
Modern types of discharge lamp have a colour rendering that is good enough for large-scale lighting inside building such as factories and warehouses. Continuing technical advances are producing more discharge lamps suitable for interior lighting high efficiency of such lamps can give significant savings in the energy use of buildings.
Mercury discharge lamps Mercury discharge lamps An uncorrected mercury lamp emits sharp light at certain blue and green wavelengths. Some Modern types of discharge lamps
In the mercury halide lamp, metallic halides are added to the basic gas discharge in order to produce better colour rendering and to raise the efficacy A metal halide gas discharge lighting system provides illumination for a college baseball game at Olsen Field in College Station, Texas. Note the various colors of the lights as they warm upOlsen FieldCollege Station, Texas
Example of a Metal Halide lighting pole, at a baseball field
Sodium discharge lamps Sodium discharge lamps Low-pressure sodium lamps produce a distinctive yellow light that is virtually monochromatic and gives poor colour rendering. however the efficacy of the lamp is very high and they have been traditionally used for street lighting
A low pressure sodium/sodium oxide (LPS/SOX) streetlamp at full powerstreetlamp
Office building illuminated by high pressure sodium lamps.
High-pressure sodium lamps SON produce a continuous spectrum without much blue light but with a colour rendering that is more acceptable than the low- pressure sodium lamp. SON lamps are used in modern street lighting and for the economic lighting of large areas such as forecourts and warehouses.
7.1.5 Lamp and energy conservation Lighting is an important area of energy conservation in buildings as new systems can be installed in existing buildings as well as in new buildings. The energy saved by a modernised lighting system usually pays for the cost of the installation within a few years, which is a shorter payback period than most methods of saving energy in buildings. The major lamp companies of the World are therefore developing new types of low-energy lamps including improvements to the compact fluorescent lamp and high pressure discharge lamps described above.
7.3 how to do Lighting design 7.3 how to do Lighting design First, find the standard service illuminance levels that are recommended for a variety of interiors and tasks given in Table 7.3. P156 The aim of Lighting design is to reach the illuminance levels Then, use Lumen method to calculate the number of lamps needed.
DLOR H m mounted height of the luminaire above the working plane table 7.4 P158 UF= utilisation factor is the ratio of the total flux reaching the working plane compared to the total flux output of the lamps table 7.4 P158 LLF=light loss factor is the ratio of the illuminance provided at some given time compared to the initial illuminance
At the end of design, we should place these lamps in a regular grid pattern and their spacing must not exceed certain distances their spacing must not exceed certain distances. This maximum spacing depends on the type of luminaire and the height at which they set. Typical values are as follows For fluorescent tubes in diffusing luminiaires S max =1.5XH m For filament lamps in direct luminaires S max =1.0XH m Figure 7.6 spacing of luminaires P160
Worked example 7.1 measuring 40m by 12m by 4m A factory space measuring 40m by 12m by 4m in height requires a service illuminance of 500lux on the work benches which are set 1m above the floor. The 65W tubular fluorescent lamps chosen have a luminous efficacy of 80lm/W. they are to be mounted on the ceiling in luminaires which have a DLOR of 50%. The room reflectances are 0.5 for the ceiling and 0.3 for the wall; the initial light loss factor is 0.7 a) Use the lumen method of design to calculate the number of lamps required b) Suggest a suitable layout for the lamp fittings.
E=? A=? F=? UF=? LLF=? So number of lamps required=144 lamps 9 rows of 16 luminaires Suggested layout: 9 rows of 16 luminaires Check spacing using Smax=1.5XHm =1.5X3=4.5m So the suggested layout is satisfactory provided that the distance between lamps is not greater than 4.5m
In a particular lighting system design,the following factors need to be considered Light quantity should reach the illuminance levels
Directional quality Energy use Costs Physical properties
Thats all for chapter 7, lets do a summary together. chapter 7 Artificial Lighting 7.1 Lamps 7.1 Lamps 7.1.1 how to evaluate the Properties of lamps Luminous efficacy Luminous efficacy Life Life The correlated colour temperature (CCT) The correlated colour temperature (CCT) Colour rendering Colour rendering
7.3 how to do Lighting design 7.3 how to do Lighting design First, find the standard service illuminance levels Then, use Lumen method to calculate the number of lamps needed. At the end of design, we place these lamps in a regular grid pattern
Practices in class 1 Modern sources of artificial light convert ( ) to ( ) A chemical energy B electrical energy C light energy D heat energy
2 Oldest sources of artificial light convert ( ) to ( ) A chemical energy B electrical energy C light energy D heat energy
3 Modern sources of artificial light are of two general types:( ) A incandescent lamps B discharge lamps C mercury discharge lamps B tungsten filament lamps
4 The following lamp is A common light bulb B spotlamp C crown-silvered lamp D tungsten-halogen lamp
5 The following lamp is A tubular fluorescent lamp B compact fluorescent lamp C mercury discharge lamp D sodium discharge lamp