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Visual and Acoustic Comfort

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Lecture – 20Visual and Acoustic ComfortWelcome back to this new lecture for the online course on Sustainable Architecture.Today’s lecture is on Visual and Acoustic Comfort. When we are talking aboutsustainable buildings and then gradually as we are moving on towards green buildingsbecause, we realize that environmental aspects, environmental parameters are the moretangible ones and hence it is easier to measure, monitor and verify them and also assessthe performance of a building as far as the environmental parameters are concerned.We largely are focusing towards the energy implications, the thermal comfort, how thebuilding performs for a given climate. However, there is an important aspect of it whichis the visual and acoustic comfort which also needs to be taken care when we aredesigning buildings and since we started talking about the sustainability in buildings.We have discussed that human beings, the occupants, the users are at the center of thesebuildings and these buildings have to be designed for the human beings keeping in mindthe comfort of these occupants. So, only thermal comfort is not the one which should beconsidered or thought about while designing the buildings, it is also the visual andacoustic comfort.Visual and acoustic comfort find mention both in our course like NBC and also in ourgreen building rating programs the voluntary rating programs which are available. Let usquickly go over each of these and what are the related concepts and terminologies thatwe should be looking at.I am sure most of you have already undergone the courses on lighting and acoustics aspart of your curriculum, if you have not some of these concepts are briefly introducedhere, but not in great detail. So, let us go over the visual comfort first. (Refer Slide Time: 02:35)So, what is visual comfort and what comprises of visual comfort? So, there are manycomponents to it. The first one which is essential for visual comfort is the source of light.So, what is the source of light? The other which contributes to it is how is it distributed.So, if it is distributed non-uniformly, so, in one place you have more light in the otherplace you have less of light then this varying distribution causes discomfort, what is thetone and color of the light that we are using.So, earlier people were using candles or flames for lighting up the interiors, gradually wemoved on to incandescent bulb and then we moved on to tube lights and now we areusing CFLs and LEDs. As the technology has progressed the quality of light the tone oflight has also changed.So, earlier we were using yellow light where the color of the light was yellow the tonewas such, and gradually we are moving to more sunlit kind of light the light white lightthat we received from direct sun. It is very similar to what we are able to produce usingthe artificial light as well.So, where there is a wide spectrum of colors available where it is a white light orcombination results in a white light is what a good color or tone of the light is. Whereverthere is a different tone or color which is there in the light, it is not usually comfortablewhen we are talking about long working hours. So, suppose assume yourself working in a space which has only red colored lights allaround you. You will not feel comfortable for long sitting in that space. The last one isits intensity. So, we need intensity sufficient enough to perform a task. Now that variesfrom activity to activity space to space, depending upon the activity and the space theintensity has to be there.Together all these 4 parameters define what visual comfort is. Visual comfort is definedas the ability to fully describe light and understand the space as it should be perceived oras it is. So, it is the absence of discomfort because of its source, distribution, the tone andcolor and its intensity and the absence of this discomfort is called as the visual comfort.So, when we are talking about visual comfortcomfort, we are talking about 2 aspects thequality, as well as the quantity. So, of these 4 parameters 2 are used to define the qualityof it.(Refer Slide Time: 05:44)First is the color of light as I just said, that color of light defines how comfortably thingscan be seen in the given light. Preferably the light’s color should be close to what thecolor of direct sunlight is which is white. We should comprise of all the colors equallyand we should be able to perceive the color of any given object as its original color andthat is what the color rendering is. So, here we are looking at the light distribution alsowhich is direct or diffuse. Now, suppose I have a lamp right on top of my head, so, there is direct light there. Whileif I have a in case of artificial light I am saying in case, of a bulb where I have a diffuserwhere I have a reflector which reflects it to the ceiling and then I get to diffused light,where I do not get any shadows, I do not get glare, same for artificial as well as naturallighting. So, what kind of light distribution is there, whether it is the direct or diffuse?In some casescases, direct light is required. For example, for a doctor who is performinga critical operation in the operation theater, there he may want to have there, we maywant to have direct light focused onto the operation area where the doctor is able toclearly see things because he is going to perform a critical operation there.Unlike when we are working or when we are reading in a classroom, there I might notrequire direct light falling onto my book, onto my notebook. I would prefer diffused lightBecause, I have to sit looking at my book for long hours and there, diffused light wouldhelp keep stress of my eyes.Another thing that we require here is freedom from glare. We will come to glare whatglare is in subsequent slides, but glare is that pinching light directly falling onto youreyes. It is not necessarily that direct light, but it is when there is a great differencebetween what my eyes are used to and suddenly when I go into a bright light or there is abright light coming from somewhere.We are also looking at the luminanceous distribution, how the luminance is distributedthroughout the work surface. So, these are the qualitative aspects of visual comfort. (Refer Slide Time: 08:30)We are also looking at the quantitative aspects of these visual comforts. Some of thesequalitative aspects can be converted into quantities. SoSo, first of all we are looking atthe illumination, how much of the light the intensity is going to be there. So, when weare talking about illumination we are talking in the units of lux and for different types oftasks from casual seeing to exceptionally severe task with minute detail as I was talkingabout the operation theater the illumination level goes on increasing.(Refer Slide Time: 08:38) So, if we are casually walking around seeing things a 100 lux100-lux illumination issufficient enough and of glare index as high as 28 is also fine because, we are casuallyseeing around things. However, when we go high on the intensity of the visual tasks forexample, we look at the ordinary task or medium detailed task which is where ourclassrooms and offices come in.We look at a anan illumination level of around 400 lux, 400 to 500 lux is what we wouldwant in our offices and classrooms and a glare index of around 25. We will come to whatglare index is. If we look at where is severe or prolonged tasks which require minutedetail for example gem cutting there the lux levels are quite high, but though the luxlevels are high we are not promoting a very high, we are not accepting a very high glareindex, the glare has to be less.So, the entire workspace has to be highly lit along with the task table, along with the taskwork plane. And the maximum it goes up to 2000 to 3000 lux which is in case ofoperation theaters or instrument making, watch making which is very minute very smallparts go in and the glare is further reduced.(Refer Slide Time: 10:43)If I look at beyond the quantity quantitative aspects of visual comfort in general, theability to control the light levels by the occupant is key to this satisfaction. So, suppose Iam in an office area where I cannot control the illumination around, today I might to be feeling a little low and I might require more light to perform a task the same task ascompared to some other days where I might want to work with less of the lightdepending upon my mood, depending upon my comfort that ability that flexibility in thebuilt environment is also a key to satisfaction.So, it is both for thermal comfort, for visual comfort equally. If I am able to control mythermal environment and, if I am able to control my visual environment, the researchershave proven that the occupant is more likely to feel comfortable be at comfort.(Refer Slide Time: 11:49)Now, we come to glare. So, glare as defined is a subjective human sensation thatdescribes light within the field of vision that is brighter than the brightness to which theeyes are adapted. Now, this brightness to which the eyes are adapted is the overallbrightness of the place, the general illumination level luminance of the place and thelight within the field of vision.So, suppose I am sitting here if you look at this picture, so, if somebody who is sittinghere is usually looking at this wall this is the work side, this is the work desk and thisside is where the bright light comes in. So, the difference between the brightness comingfrom this side versus the brightness which is prevailing in this larger area this room iswhat is perceived as glare and there are quantified formula to define what glare is, butglare is often harmful. Because, it injures the eye, it disturbs the nervous system and at times it when we aretalking about injuring the eye it almost blinds a person you cannot see. It is a cause ofannoyance, discomfort and fatigue. So, if you are constantly, for example, if you aredriving during the night and there are vehicles coming from the opposite direction, so,your eyes are used to a much lower level of brightness because it is night and suddenlywhen the light from the vehicle which is coming from opposite side hits your eyes that iswhat causes a discomfort because of glare.Now, constant exposure to this glare causes fatigue; it is mental fatigue, it is fatigue toeyes, it is fatigue to body. So, itsit reduces the efficiency of work and it interferes with aclear vision which is what I say that people are almost blinded when there is glare whenthere is high glare and thereby increasing the risk of accidents.So, a lot of accidents happen because of this glare on highways. So, I am giving exampleof glare from highways, but when we are talk about the buildingsbuildings, weexperience a lot of glare coming because of surrounding buildings. So, suppose I have awindow and there is a reflection coming from the building which is adjacent because ofthe light coloredlight-colored finish of that building a lot of reflection of light is comingonto my window and onto my eyes. So, that is how the glare inside a building oftencomes in.(Refer Slide Time: 14:39). So, to define glare the glare index has been defined which is what we just saw when wewere defining the illumination level and the glare indices. So, the formula inn corporateslargely the luminance of the glare source which is under question, the average luminanceof the field of view to which the eyes have adjusted, the position index of the glaresource how far or how close it is to the object to the area under study subject under studyand the subtended area of the glare source.Put together in a formula it gives us the glare index. With the help of this glare index aswe have already seen we can define how much of glare is ok. So, up to 25 is maximumthat can be seen that can be accommodated this is as per CIBSE glare index, but there isa new glare rating which is unified glare rating or UGR.(Refer Slide Time: 15:46)And it is defined by this formula again where we are taking into account the backgroundluminance, we are taking into account the luminance of the source and the luminary, andputting together in an formal in a formula to get the UGR as per the UGR we are lookingat a limit of UGR 16 which is good enough for the human eyes beyond 16 it is notadvisable to have the glare. Now when we have talked about the illumination level theluminance and the glare index always whenever we are talking about visualcomfortcomfort, we are talking about 2 things. We have to look at strategies to control glare and to allow for this minimum illuminationwhich is desirable besides these 2 the qualitative parameters where we were talkingabout the color of light and we are talking about the uniform distribution the tone of thelight, the tone color and uniform distribution also comes into a picture and one morething which is the direct access to views. So, how much can we view.(Refer Slide Time: 17:09)So, this is a beautiful illustration which is put up by Elisa Gehin and it is available inpublic domain at the Saint Gobain website. So, there are 6, 7 strategies or indicators toassess visual comfort. First of allall, which we of a neglect is an access to views this isvery well taken care in green buildings in sustainable building where each workplaceshould have an access to views.If every workplace cannot be connected to the outdoors outside the building, puncturesor green areas natural areas within the building have to be created in order to provide forthese views. The next is provision of sufficient day light every workplace should be daylit as much as possible. Though we may have sufficient light available artificially yet theprovision of daylight has a lot of impact now we may not be able to perceive thatimmediately.But if human beings are continuously exposed to controlled environments where theycannot see the daylight there are psychological changes which start to happen which are visible and a lot of medical research has proved that. So, direct provision of daylight insufficient quantity is required for visual comfort. Tthe next is uniform distribution of thatwe cannot have some workplaces with limited daylight availability and others with lessof that.If it is a uniform distribution that is what will lead towards the visual comfort then we arelooking at a good combination of natural and artificial light for some for the entire yearfor all the working hours it is very difficult almost impossible to provide for provision ofday light to all the workspaces. So, we have to have a good combination of artificial andnatural light preferably day lit areas which are which are receiving good amount ofdiffused light daylight, day lit combined with provision of artificial light in addition tothat we should have adequate task lighting.So, there may be general lighting in a space and then specific task lighting dependingupon an individual’s need which also fulfills the need of an individual to control his ownenvironment. Maybe I need more light to work and there is someone who prefers lowlevels of light to work. So, that personalization of a space giving individual controls iswhat can be fulfilled through provision of adequate task lighting.The next is the ability to ensure the absence of glare and high contrast. So, we should usesuch fixtures such luminaries where we are able to control the glare the next is anaesthetically pleasing space this is a very qualitative aspect, but any space which is ifesthetically pleasing, beautifully designed interiors and environments enhance theproductivity of people they become they feel more energetic they feel more activated towork. So, these are few parameters which we can keep while designing any space forvisual comfort. (Refer Slide Time: 21:03)And this is based upon a lot of socio psychological research where it has beenestablished that goodgood we visual comfort, good amount of light, but type of light,quality of light, amount and intensity of it. Actually, has a significant effect on how wefeel how we experience in a space and in time both consciously and subconsciously. So,we have to provide for good visual comfort now some of the visual comfort strategieswhich can be employed to bring in visual comfort passively are shown here on this slide.(Refer Slide Time: 21:41) So, we can use light well we can use roof monitors and atriums where a lot of daylightcan be brought into the atrium the courtyards actually served such a purpose there arelight ducts. So, this is the reflective side of the material where the light is actuallyreflected it is mirror and if you remember, if you have seen some of the old photos andtraditional buildings, mirrors were used to bring in light to the deep corridors to the deepareas inside the buildings.Light shelves we have discussed again this top surface of the light shelf is a reflectivesurface and it reflects and this light which has received indoors is actually a diffusedlight similar to light shelf we have a shelf here. So, it is slightly different from this lightshelf, but serves the same purpose of reflecting the light and then diffusing it.We have clear story again reflective surface here direct as well as diffused penetratesinside and we have reflective blinds here which are serving similar purpose as the lightshelves smaller light shelves as we can see here. Another very interesting strategy whichis utilized in case none of these is working is to divide the window in such a manner.(Refer Slide Time: 23:20)That a large window where we have a large window we can divide it the portion abovethe visual part of the window is where the clear glass is used and that part is used toreflect the light to bring in light and penetrated deeper while this part of the window wewill use a tinted glass now this will help in cutting down the glare. So, there will be no direct light falling onto the eyes of the occupants and there is; however, there issufficient light which is brought in through the clear glass which is above.So, the window very clearly can be divided into 2 parts and just by choice of the color ofglass interesting combinations and overall a uniform distribution of light can beachieved. So, this particular case study shows how different day lighting strategies havebeen used to day lit almost the entire school. So, this is the case study of a school wheredifferent strategies have been used to bring in diffused daylight into the habitable rooms.(Refer Slide Time: 24:49)NextNext, we have acoustic comfort. Now when we are talking about acousticcomfortcomfort, we must very clearly understand the difference between sound andnoise. So, sound is what we have desired and we have designed for while noise issomething which is unwanted and we have to design out. For example, I often take thisexample of a classroom. So, when as a teacher I am in the classroom what I am sayingthe lecture that I am delivering and what my students are able to hear is what the soundis.I should be hear able to hear what my students have to say they have to ask and thestudents should be able to hear me what I am delivering. While noise is something whichis what we do not desire in this space for example, somebody walking in the corridor outside my classroom, a vehicle going by the side of the classroom on the road. So, allthese noises are unwanted.So, we want to hear each other clearly while in a classroom, but we do not, do not wantany of the noises coming from outdoors to inside of this room that is nice for me. Nowhow do we know how much of the sound is available or should be allowed? How muchof the noise should be cut?(Refer Slide Time: 26:02)So, first of all we have to measure I am sure you have already read the course onacoustics where you know how we measure. So, we measure using decibels. So, Decibelis the unit for expressing the ratio between the 2 physical quantities for measuring therelative loudness of sounds. If you look at the average decibels which are required in anoffice and in a classroom around 60 decibels is what we would normally require that is,that is what should be maintained extremely low decibels spaces which are too quiet arealso not comfortable we might be comfortable in those spaces for a very short while.So, there was an experiment which was conducted and one of the universities in a UnitedStates where they were able to bring down the decibels in a space down to 0. So, anabsolutely quiet space and at 0 decibels the human beings we can hear our own bloodflowing through our body and it is quite disturbing. So, we need a little sound around us which is around 30 decibels is good. 30 decibels isis where you have the leaves rustling,you have the sounds of the nature, little bit of whisper and it is quite comfortable.If we look at 40 decibels this is what we require for sleeping. So, around 30 to 40 decibelwe can comfortably sleep. 60 is what we would look at what we want in the classroomsslightly higher than that is what we would look at of we would be comfortable when weare in an office space where people are moving, people are talking.There are little discussions going on. When we have a somesome average radio beingplayed little bit of music, vacuum cleaner and all that is around 75 decibels. Now 80, 85is the limit beyond this it is harmful for the ears. So, any sound above 80, 85 decibels isnoise, beneath this also depending upon the space it is it may be qualifying as noiseabove this it is definitely harmful and noise.(Refer Slide Time: 28:42)So, depending upon the quietness that you require or the amount of sound that yourequire the space has to be designed it will impact the health of the occupants the amountof sound which is present amount of noise which is present it depends upon waitinglevels of privacy. So, in areas which are more private suppose I want to have a privatediscussion in a conference room even when I am in an office such areas would requiremore acoustic treatment. (Refer Slide Time: 29:42)For example, the theaters they require more sound acoustic treatment to provide for thesound quality. So, when we are looking at the design of buildings for acousticcomfortcomfort, we should look at the transmission path we should identify the source,we should identify the receiver and we should look at how what the path of this soundtravel is from source to the receiver.(Refer Slide Time: 29:53)Based upon this we have to identify the strategies we have to look at these strategies fordesigning these buildings. The impact of this environmental noise can be direct as well as indirect on human health and wellbeing people expeexperiencediency sleepdisturbances, speech interferences and annoyance.(Refer Slide Time: 30:03)Because of the environmental noise there is a reduced productivity and there is aprolonged patient recovery that is why in all the hospitals where patients are, people arethere with illnesses, sicknesses. The hospitals are supposed to be maintained quiet. Sinceit reduces the retention, concentration of occupants those classrooms and work areas likeoffices are also required to be maintained at low decibel levels.(Refer Slide Time: 30:50) When we are talking about buildings, we are talking about many concerns, we arelooking at environmental noise; we are looking at mechanical and equipment noisewhich is often a very high noises a major concern. We have HVAC systems, we have airconditioners, on our windows and inside our rooms we have water coolers, we have fans,we have different equipment which is there.So, a lot of noise is because of these mechanical or other equipments we also havestructural vibrations which are passing from the; which are passing through the structureof the building into the space. We have concerns for speech privacy as I would justmentioning for conference rooms, meeting rooms we have requirements for roomacoustics and sound isolation is what we require we need to isolate the source where thesound is coming from the noise is coming from.. .(Refer Slide Time: 32:00)For doing that we have to understand very quickly some of the phenomena some of thequantities parameters that we use one most important is absorption coefficient. Nowwhat is the absorption coefficient very simply if I put it is the proportion percentage ofthe not percentage. It is the proportion of the sound which is absorbed by a surfaceversus its total incident sound energy which is incident on the surface. So, the moreamount of sound which is absorbed by it out of the incident sound is what its absorptioncoefficient is higher is that amount, higher is the absorption coefficient. Maximum it can be 1 because 100 percent of the sound is absorbed and least would be 0where all the sound is transmitted. For example, an open window so, an open windowhave, will have all the sound transmitted through it. So, that is where the comparisonwould be just as we have lightlight, we have the phenomena for sound. So, the sound isreflected from the surface the harder the surface is the more is the sound which isreflected then we have absorption by the surface. So, the more porous the material is themore is the amount of sound it absorbs.So, a material such as wool voile or fabric because it is porous absorbs more amount ofsound and then there is diffused. So, based upon the shape of the; shape of the materialthe amount the sound when it is incident on this it is diffused. So, it is broken into soundof reduced intensity, but it is there it is still there it is reflected that is what diffusion isthe next concept that we have to keep into mind is reverberation.(Refer Slide Time: 34:12)So, reverberation is prolongation of the sound in the room caused by continued multiplereflections which is what we would see in case of different shapes. So, it gets reflectedfrom one surface goes onto the other surface and then further reflected and comes back.So, it will happen only when we have hard surfaces and there are multiple reflectivesurfaces present in any room. That is what will also cause the echo now based on reverberation and the formula we cancalculate the reverberation time.(Refer Slide Time: 34:45)Now this reverberation time decides for how long the sound is going to be present in thatspace for any general purposegeneral-purpose auditorium which is both for speech andmusic now there are different reverberation times which are proposed good for musicand separately for speech. So, for any music to be enjoyed for a theater where musicalperformances are going to be a reverberation time of around 2.5, 3.5 is good. So, whenwe have a reverberation or time of 3.5.Because, there are different types, different intensities, different notes, different musicalwaves which are hitting our ears that is where the musical sound will sound fuller, richer.if we have less reverberation time less than 1 it will it will be perceived as a very deadspace it will be perceived as a very dead sound while it may be good for speech. So,around 1.5 seconds of reverberation is good for speech it is a little bit of hard surfacesshould also be there that is when it sounds good.Now that is this reverberation time is calculated on the basis of the total surface areaequaequivalentl and surface area which takes into account the absorptivity, theabsorption coefficient of the surface and the surface area. All the different surfaces and theretheir absorption coefficients put together and also the volume of the space sotogether these 2 result in a reverberation time.