Bilgisayarla Çalışılan Ofislerde Konforsuzluk Kamaşması Denetimi Sağlayan Yapma Aydınlatma Sistemlerinin Tasarımı Ve Uygulaması

Abstract

Of isler, insanların belirli konular üzerinde düşünsel ve görsel çalışmalar, sözlü ve yazılı iletişim imkanlarıyla do laylı veya yüzyüze görüşmeler yaptıkları binalardır. Of is ça lışanları günlerinin önemli bir bölümünü bu hacimlerde geçir diklerinden en etkin çalışma ortamının oluşturulması için tüm alt sistemlerin, çalışanların ihtiyaçlarına en üst seviyede cevap verebilir nitelikte olması gerekir Gelişen kompüter teknolojisiyle beraber, VDT' lerin (Video Display Terminals) pekçok çalışma sahasıyla birlikte ofisler de de kullanılması kaçınılmaz olmuştur.Ancak bilgisayarla ça lışmak bazı durumlarda kullanıcıların şikayetlerine yol aça bilmektedir.Bunlardan bazıları ergonometrik koşullarla ilgi liyken bazıları da tamamen aydınlatmayla ilgilidir. Bilgisayarla çalışılan ofislerde aydınlatmayla ilgili en büyük sorun, yapma aydınlatma armatürlerinin ekranda yansıya rak etkili görüntü oluşturmaları ve ekranla ekran üzerindeki karakterler arasındaki parıltı karşıtlığının düşürülmesidir. Bu da ekrandaki yazı ve şekillerin algılanamaması veya karış tırılması gibi şikayetlere yol açmaktadır. Bu çalışmada ofis binaları tasarımının tarihsel gel işi mi, bu gelişim sürecinde ofis organizasyonunda, yer leşim düze ninde, çal ışanların sosyal statülerinde ve ofis işlevlerinde meydana gelen değişimler 1. Bölüm'de ele alınmıştır. 2. Bölüm' de genel olarak ofis aydınlatması ele alınmış tır. Görsel çevre etkenleri (aydınlık düzeyi, parıltı ve renk) ve bunların alması gereken değerler, of is aydınlatmasında kul lanılan aydınlatma sistemleri..aydınlatma kontrolü ve özellik le bilgisayarlı aydınlatma kontrolü, çeşitli ofis alanları i- çin aydınlatma tasarımı kriterleri bu bölümde açıklanmıştır. 3-Bölüm'de ise, ofis çalışanlarının fizyolojik gereksi nimlerini karşılayan alt sistemler ve bunların yapma aydın latma alt sistemiyle entegrasyonu ele al inmiştir.îkl imlendir me ve aydınlatma fonksiyonlarını birlikte gerçekleştiren hava kanallı armatürler, aydınlatma armatürlerinin ofis hacimlerin de akustik sistemlerle birlikte kul lanımı.günışıgı ile yapma aydınlatmanın entegrasyonu bu bölümde açıklanmıştır. 4.Bölüm'de bilgisayarla çalışıan ofislerin aydınlatılma sı ele alınmıştır.VDT ve ekipmanlarının tanıtı iması, kullanım alanları.kullanıcı şikayetleri, kul lanı lan aydınlatma sistem leri açıklanmıştır. 5.Bölüm'de.bilgisayarla çalışılan ofislerde kullanıcı ____., _______ _.:-...._ ?_._.__. _____..._...». _..._._. . - ıforsuzluk inmiştir. 5.Bölüm'de.bilgisayarla çalışılan ofislerde kul şikayetlerinin büyük bir çoğunluğunu oluşturan konfo kamaşmasının değerlendirilmesi ve denetimi ele alırım XVII Kamaşmanın tanımı.nedenleri.kamaşmanın değerlendirilmesinde kullanılan yöntemler ve karşılaştırma tabi o lan, kamaşma dene timi sağlayan nomogramlar ve bu nomogramlar yardımıyla yapma aydınlatma armatürlerinin limit radyasyon ve örtüleme açıla rının hesaplanması açıklanmıştır. ö.Bölüm'de ise,bi Igisayarla çalışılan ofislerde kamaşma denetimi sağlayan örtüleme tekniği programı, bu teknikle ge liştirilen aşağı doğru genel aydınlatma armatürlerinin ka maşma denetimi ve hacim içindeki yatay ve düşey aydınlık dengesine etkileri açıklanmış ve örnek bir VDT için standart ların belirlediği VDT geometrisi içinde uygulamalar yapılmış tır. 7.Bölüm'de sonuç olarak, VDT' lerin aydınlatma sistemi a- sagı doğru genel aydınlatma sistemi ile tasarlanacak ve ger çekleştirilecek ise, bu sistemi oluşturacak armatürlerin.ka maşma denetimini en iyi şekilde gerçekleştirecek örtüleme a- çısının ne olması gerektiğine karar veri lecektir. Ayrıca bu çalışmanın bundan sonra yapılacak ne gibi çalışmalara temel olabileceği konusunda görüşlere yer verilmiştir.

In workplaces, feelings of wel 1 -being, interest and enthu siasm are very important to productivity and affected by the physical environment. It ' s clear that the lighting should be designed to make the physical environment as pleasant as pos sible. In the long process of the historical developments, the layout, the organisation and the workers of an office changed. In 1900, only 20 per cent of "Professional" employees were "White-Collar" workers but today this ratio stands at 50 per cent. In the sixtees,cel lular premises were replaced by the "Landscape" or Open-plan of fice.Open-plan would enable im proved communication, closer teamwork, more flexibility and the space effectiveness. But in the light of modern day experience the charges levelled at Open-plan are not inconsiderable : Lack of privacy, limited flexibility and acoustics and aii - condi tion problems. As a result, both cellular and landscape layouts have now been superseded by a third kind of office named"Ac- tion Of fice". It has the advantages of both the cellular and the landscape office. There's a direct relationship between the office layout and the office organisation. Hence the cellular office, each individual worked more or less independently in his own style named"Pre-Industrial Era".Secondly, where work was organised as on a production line, for which the open-plan office was a good solution, named" Industrial Of fice". The present phase is "Information Of fice".Workers with easy to the data base of computers through Video Display Terminals (VDT) handle large quantities of information. In the past, recommendations for office lighting were based on horizontal illuminance at the working plane neces sary for tasks like reading and writing of dark text on white paper. In the last 30 years, as the office work is changing, to ward more communication with colleagues and office machines -like video display screens-which involves viewing of verti cal surfaces, the visual requirements of office workers are also changing; and it's necessary that the lighting be design ed accordingly. Video Display Terminals have now become standard equip ment in workplaces; the range extends from word-processors to CAD systems and computer aided production systems. Tnis fact has important consequences for light as planning VDT work stations make particularly exacting demands on the design of lighting systems. The reason for this is the relatively low XIX contrast between the screens and the symbols or lines shown on them. The contrast can be further reduced by the reflection of bright areas off the screen. Therefore, in lighting VDT workstations, special attention is to be paid to the luminance balance within the room, especially to the optimum reduction of glare from the luminaires. As far as the lighting is concerned, an office worker requires that; - This could enable him to perform his visual task or tasks with ease, speed and accuracy (good visual performance) - It should help create a stimulating and visually com fortable atmosphere in which to work, whilst also improving his feelings of well-being (good visual satisfaction) The lighting system should be integrated with the acous tical system, with the ceiling system, with the mechanical and the electrical systems and with the interior design. Heating ventilating and air-conditioning (HVAC) systems may be closely integrated since air handling luminaires are avaible. Air may be supplied or returned via slots on each sides of the iuminaire.The interior design and the lighting of a space ideally should be integrated so that light complements the interior design and the design accomodates the lighting. For instance, an architectural cove provides an opportunity to hide lighting equipment. Office lighting must be adequate for work after dusk whether or not there are windows. During the day »daylight can replace some electric lighting. Many reasons can be put for ward to justify using daylight as a light source in a build ing. Among the reasons are:quality of daylight, importance of daylight as a design element, view out (daylight apertures provide visual contact with the world outside), the desire to have natural light in a room or space, dynamic nature of day light and energy concervation resulting from the use of day light. One way of integrating daylight with electric light is to circuit perimeter luminaires on a seperate switch which may be manually or photoelectrical ly switched or dimmed. Ho rizontal, vertical or roller blinds or refractors can control brightness or to some extent redirect bright light in useful directions. When we look at the general recommendations of office lighting; at first illuminance level and uniformity : for the vast majority of the office tasks, the working plane is usual ly horizontal at a height of between 0,75m. and 0,85m. above floor level.Research into the illuminances preferred in work ing interiors has shown that there is no value at which everyone is satisfied. Added to this is the fact that various XX office tasks are often being performed simultaneously in one and the same of fice. The recommended average illuminances on workplane for various types of office interiors and office tasks are given in Codes. In the case of general lighting, the ratio of the minimum to the average illuminance (Emin/Eav) should be greater than 0,8. The ratio between the average illuminances for any two adjacent areas should not exceed 5:1 Excessively large differences in luminance in an office can create visual adaptation problems or, in extreme cases, glare.Conversely, if the luminance differences are too small, the surroundings will appear dull and uninteresting. Both these effects can be avoided by ensuring the luminance ratios in the field of view, are between 10:1 and 3:1. The luminance ratio between the visual task itself and its immediate back ground should be smaller than 3:1, -but greater than 1:1. Glare is experienced if lamps, lumina i res, windows or other areas are too bright compared with the general brightness in the interior. People respond to the colours they see about them. In these offices where workers are exposed to an environment for long periods, the colour in that environment can influence their work performance and is sure to have some effect on the degree of the visual satisfaction experienced. The colour scheme in an office, that is to say the colours of the furni ture..the wall and the ceiling coverings, is influenced in no small degree by the colour characteristics of the ligt sources used. Two important aspects of the colour properties of light sources have to be distinguished: l.The colour appearance of the light source. This is the colour impression received when looking at the source itself. It depends on the illuminance level, the presence or absence of daylight, climatic conditions and personel preference. 2. The colour rendering of the light source. This is the ability of the light to faithfully reproduce the colours of an object by it. Light sources with a colour rendering index (Ra) of at least 0,8 are recommended for all offices. The most common primary lighting systems, as far as the layout and the location of the luminaires are concerned are: 1. General Lighting: Provided by a regular pattern of lu minaires. 2. Localised General Lighting: Provided by an irregular pattern of luminaires related to the working zones in the office. 3. General + Local Lighting:The low-level general light ing being supplemented by additional luminaires at the work station. XXI In principle, in all these systems the general lighting can be realised with direct, indirect or combined direct and indirect lighting. In direct lighting (Downlighting),as the name suggest, this involves the use of luminaires whose light emitting surface is directed downwards. In indirect lighting (Uplighting), the light emitting surface of the luminaire which is above eye-height to avoid problems with glare, is aimed upwards, with the light being reflected downwards from the ceiling and wal Is.Combination of direct and indirect lighting can be obtained by using two different types of luminaires in one and the same space or by using a so-called "direct-indirect" luminaire that has both a downward and upward component. An important part of the running costs of a lighting installation consists of energy costs. Savings on these energy costs is possible by controlling the lighting in such a way that the lighting level is always accurately matched to the actual need. Another reason for wishing to control the light ing has to do with human comfort and efficiency, both of which can be improved if the persons concerned are able to adjust the lighting to suit their personal needs and preferences.The illuminance level in a room can be controlled in a number of ways: - Switching (Stepwise Control) - Dimming (Continous Control) - A Combination of switching and dimming Lighting control systems fall into three categories: 1. Manua 1 Contro 1 2. Automatic Control (Non-Intelligent) 3. Computer Control (Intelligent) For different specific areas, there are different design issues. Open plan office is a relatively large space shared by a number of people. It may contain only desks, or in addition there may be free standing screens or panels to divide the space to the individual work areas. Since the space is large, each worker may see a large area of the ceiling. To prevent glare, it's therefore important to limit the brightness of the luminaires (or the ceiling itself in the case of indirect lighting) in the glare causing emission angles between hori zontal and 45 degrees. When system furniture is used, the pa nels and shelves may cause shadows on the work surf-ace.These shadows may be overcome by using local task lighting. A private office is generally relatively small space for one occupant.Since there is one occupant, the lighting may be designed specifically for the occupant. In conference rooms, the conference table should be adequately covered by the ge neral lighting. The supplementary lighting should be provided with a switching or dimming control to facilitate the showing XXII of slides or films. Visual requirements for drafting demand high quality illumination since discrimination of fine detail is frequently required for extended periods of time. Reception areas are designed for people who are wait ing. While they're waiting they may read or hold discussion. The lighting should be restful yet provide enough illumina tion for reading. One way to provide a restful atmosphere without direct glare is by illuminating one or more of the wa 1 1 s. Public areas in a building generally include entrance and elevator or escalator lobbies, corridors and stairways. Since many people move through these areas, lighting consider ations should include safety requirements and luminance differences with adjacent areas in addition to the appearance of the space. Since many public areas are agress areas, a com plete auxiliary lighting system is required to cope with power outages and system failures. VIDEO DISPLAY TERMINALS To understand the problems of correct lighting for VDTs the types of VDTs available and their applications in modern working environment should first be considered. Visul display terminal is a functional unit equipped with a display screen and also an input unit (keyboard).Display screen is a part of an assembly unit designed for the variable, electro-optical display of characters and graphics.Display screens are dis tinguished according to the whether they display light characters on a dark background (Negative Display), or dark characters on a light background (Positive Display).Keyboard is the most frequently used means of data entry and control of individual VDTs. The VDTs are used in wide range of appli cations from simple display of calculations to complex graph ical represantations. Work at VDTs involves two distinct visual tasks: 1. Taking in information displayed on the screen. (e.g. re ading texts, studying graphical represantations, monitoring technical process with the aid of television pictures). 2. Taking in information not displayed on the screen (e.g. reading texts of source documents, studying graphical represantations, reading symbols on keyboard, reading off data on indicating devices, monitoring technical routines) Each of these visual tasks makes differing demands on the lighting. The requirements that artificial lighting must meet primarily refer to the following photometric characteristics: XXIII a-Level of illumination b-Luminance distribution c-Restriction of glare d-Direction of light and shadow ratio e-Colour of light and colour rendering properties The above characteristics are also applicable in the case of rooms in which VDT workstations are instal led, but the special recommendations shall be taken into account for the level of i 1 luminat i on. luminance distribution and restriction of glare. A further quality characteristic, specif ic to VDT applications is; f-Avoidance of veiling reflection due to light surfaces (windows, luminaires, etc. ) being reflected on the screen. High luminance reflections from the display screens-as a complaint by the VDT user-can take several different forms. The simplest to consider is a reflection which is spread uni formly over the screen. Tnis reduces the contrast between the screen characters and the screen background. Such reflections may cause a reduction in visual performance and adversely affect people's satisfaction with the display. The choice of correct illuminance at the VDT workstation is very important.When it's too low, it will reduce the visual performance for conventional work, while if it's too high it can result in a reduction in character contrast on the VDT screen. Research and experiences indicate that the optimum illuminance is 500 Ix. Surface design and luminance distribution are of espe cial importance in rooms in which VDT workstations are in stal led. Since luminance distribution is a predominantly func tion of the photometric properties of surf aces. The reflect ance, gloss and colour of the surfaces at and around the work place shall be selected with a view to avoiding extreme differences in luminance and veiling reflection from light sources. The colours chosen for furnishing shall be of medium sat ura t i on, while the colours of walls and ceiling shall be of low saturation(pastel shades).Light coloured clothing of the operator may also cause veiling reflection on the screen. In order to achieve a comfortable balance öf luminances in the VDT environment and limit the effects of transient adaptation and glare, luminance ratios should not exceed; - Paper-base task to VDT screen 1 to 1/3 - Task and adjacent dark surrounding i to 1/3 - Task and adjacent light surrounding 1 to 3 - Task and more remote darker surfaces 1 to 1/10 - Task and more remote lighter surfaces 1 to 10 Tne restriction of direct glare by luminaires in the XXIV critical zone (from 45 to 85 degrees) of the angle of radia tion shall at least meet the requirements for Quality Class 1 according to CIE Glare Safeguard System. The Visual Comfort Probability (VCP) of the luminaire with direct components should be 80 or more. Reflected glare, the reflection of light areas on glossy surfaces, impairs the assimilation £>f visual information »but it can be restricted if duly taken into account in the design of the equipment and other objects in the room. Since the occurence of specular reflection is a function of the angle of incidence or viewing angle, particular attention must be paid to the direction from which the light is incident, and hence to the arrangement of the workplaces and VDTs,as well as to the location of the luminaires and to their luminance distribution. Wall surfaces (and other peripheral surfaces) »windows and furnishings that are reflected on the display screen shall have a mean luminance not exceeding 200 cd/m2 and a maksimum luminance of 400 cd/m2.The luminous surfaces of luminaires reflected on the display screen shall have a mean luminance not exceeding 200 cd/m2 in planes Co,C90,C180 and C27Q for an angle of radiation greater than the 1 imt angle of radiation. The limit angle of radiation is a function of the view ing distance, of the size of the screen, of its radius of cur vature and angle of incl ination, as well as of the angle be tween the line of sight to the top line of the display and the horizontal. Luminaires that are reflected on the display screen shall have a minimum shielding angle of 30 degrees in planes Co, C90.C180 and C270. If the geometrical data of the VDT and the corresspond- ing workplace are known, then the relationship between these data and the limit angle of radiation can be determined by means of the nomograms. I f the geometrical data of the VDT and workplace required for determinig the limit angle of radia tion are not known,when the lighting system is being design ed or if, owing to the room configuration, veiling reflection may be expected to occur no matter how the VDTs are arranged, the luminaires that may be reflected on display screens shall be designed to maintain a limit angle of radiation of 50. For most applications, provision shall be made for gene ral lighting, or for general lighting oriented to the work places.Supplementary local lighting of the workplaces is only permissible if it can be ensured that the direct and reflect ed glare and the luminance ratios obtaining between screen, keyboard, source document and adjacent surfaces are not unduly increased in consequence. XXV Indirect lighting or a combination of direct and indi rect lighting may be a suitable means of avoiding veiling reflection of light surfaces on the display screen, on the other workplace equipment and on the horizontal working sur face. The succesfui performance of visual tasks associated with work at VDT workstations can be seriously impeded by veiling reflection and by an unfavourable distribution of luminance within the room. For this reason, the selection of luminaires and equipment for work of this nature, and their arrangement in the room, must be largely guided by photometric considerations.Luminaires should not be arranged directly above VDTs,but set to one side. The arrangement of the VDTs within the room is generally dictated by the location of the windows, with strip lighting or rows of luminaires running paralel to the main row of windows. To prevent unduly high level of illumination occuring on the display screen due to daylight, the VDTs shall not be installed too close to windows. As this requirement can not generally be complied with in the case of small rooms, shield ing measures may then be needed. Windows in or against the line of side shall be provided with shields in order to pre vent direct or reflected glare and veiling reflection due to daylight.Suitable shields for glare protection purposes are, for example, curtains, blinds or etc. All such furnishings shall have a low radiant transmittance and a reflectance matching that of the walls. The view to the outside shall not be ob structed. If only a few VDTs or VDT workplaces are installed in large rooms-like open plan offices-measures designed to shield individual units or workplaces may be adequate for the application concerned. Examples of localised solutions.- - setting up room dividers - suspending screens from ceiling - anti-reflectance measures on the display screen Cut-off is a shielding technique (especially lamps or too bright interior surfaces of luminaires) to restrict glare. Downl ight reflectors that have consistent cut-off angles for a variety of lamps and apertures, are developed by sophisti cated computer programs.Within this cut-off angle, there is no disturbing glare. This is the characteristic feature of dark- light technique.lt combines both the maksimum visual comfort with the maksimum output ratio and a balanced relation be tween horizontal and vertical illuminances. As a result of photometric studies, minimum standards for lighting VDT workstations have been formulated. For a critical limiting case of this type, the standard requires that lumina ires which could be reflected by the screen must have a cut- XXVI 4 off angle of at least 40* (a limiting radiation angle of 50') beyond this angle the reflector luminance may not exceed 200 cd/m2.A 30* cut-off (limiting radiation angle of 60") is suitable for VDT supported workstations, i.e. where the use of VDT is occasional. Luminaires that have cut-off angle of 40" provide balanced relation between horizontal and vertical illuminance uniformity of horizontal illuminance and good glare limita tion. Luminaires that have cut-off angle of 30° provide high vertical i 1 luminance, good uniformity of i 1 luminance.even in low-ceiling rooms but with less controlled specular reflec tion.