Lecture – 11 Illumination Systems I


Yeah, welcome to the next lecture on illumination
engineer and electrical utility services. This is the eleventh in series, titled illumination
systems I. Having understood the need for illumination
and having understood that the requirement for artificial illumination systems arises
from the fact that the life cycle or the activities of the human beings are centered around the
sunlight, the natural radiation and all our systems are trying to get the spectrum as
close to the spectrum that due to sunlight. And having understood the way sun light functions
and looking at the way the human eye response to these light, we had a look at the various
possible systems that could be used to get the artificial lights. And any of these artificial sources had to
use some kind of a physical phenomena and having got these sources, it becomes necessary
to look at the complete lighting system which we call illumination systems. So the instructional objectives for the lesson
could be listed as, list the components of an illumination system. That is apart from the source yes, there is
a source which can give certain life flux but we have to make it available on the surface
or the task surface or the object of interest. Recall that human eyes are most responsible
for acquisition of information and it is through eyes that more than 80% of the information
is acquired by the human beings. Now in this context of trying to have the
light available on the task surface, a luminaire becomes important. So, the next instructional objective would
be what is a luminaire and what are the various forms of lighting. Look at the spectrum of activities that we
have. We have activities broadly categorized as
what goes on inside a building, home, office which we can call as interior lighting. As against this we have activities outside
which could be commuting from place to place using the high ways. Streets, roads which could come under the
category of highway or street lighting. Second thing could be sports which should
come under the sports lighting and we also have lighting requirements for our manufacturing
processes which we can call it as an industrial lighting. So this is what could be addressed in various
forms of lighting. So illumination systems are being looked after
the thing to be borne in mind is the natural radiation due to sun is what enables us to
perceive things and eyes are enabling us to perceive, we had a complete look at how eye
sensitivity depends or how eye response to the light and we find that the peak response
of human eye is very close to the peak energy content in the visible spectrum of natural
light. Incidentally if you want to classify a light
due to a solar radiation, it can be classified as three major zones. One, the ultra violet, two, the visible zone
spread over violet to red and then the infra-red. So there comes the need to establish a similar
light. In doing this we use artificial sources, in
fact the whole course is about that. So we find that there are certain physical
processes that are responsible for getting these. The fundamental process had been the process
of incandescence that is materials being maintained at a higher temperature, incandescent lamp
in fact evolved from the original wax candle or oil lamp, gas lamp to today’s incandescent
lamp. Now that is the material is being maintained
at a higher temperature in that higher the temperature better is the illumination index
and the advantage of this has been that it produces a near uniform or a continuous spectrum. On the other hand the other physical processes
like electroluminescence which essentially concession having a discharge luminous discharge
in a gas or a metal vapor by application of an electric field is what we call electroluminescence
and based on this we have neon signs which are used mainly for display or advertising
and then sodium vapor lamps, mercury vapor lamps. The major lacuna of these discharges is that
they are not continuous spectrum. They are line bands or you have band spectra
are predominant over a particular zone of the visible red spectrum and hence you do
not get uniform white light, the way we get in an incandescent lamp and over and above
this, we have a third physical process which we call fluorescence which we are using extensively. It exploits the fact that there is a certain
amount of radiant energy available in a mercury vapor discharge in the ultra violet zone which
when observed by certain chemicals known as phosphors can be reradiated in the visible
spectrum and that is called fluorescence. And we saw the need for moving from incandescent
to florescence has come from another important requirement on illumination sources in the
sense they are to be economical or it needs to be reduced or increase the light flux for
every watt of energy consumed and that is where we set the… Efficacy of light sources is talked about
in terms of lumens per watt and that is how we move from though in case of a discharge
lamps, we get a line spectrum or a band spectrum we find in the view of their higher efficacy
they are preferred. Now in trying to assess all this, it needs
to understand the laws that these systems follow just as any other physical system the
illumination or the light flux also follows the certain laws. We have a square law, inverse square law of
illumination and that’s how we looked into the laws of illumination and no system is
complete unless you are able to measure and that is where the principles of photometric
where discussed. Right from the point of view of standardizing
light output, we said intensity of light can be standardized as a candle law. We have seen how a fuse, a perfect black radiator
maintained at the freezing temperature of a platinum was chosen as a standard. And now the total light flux coming out of
a lamp is what we categorized as lumens. And if we consider the original candle or
incandescing lamp we can view it as a point source and if we draw imaginary swear. The total thing that comes out is over the
total solid angle of 4 phi radians is what we call 4 phi i lumens where i is the candle
power of the lamp at the center. Now, having defined that way then we look
at the effect of this light falling on a source that is talked in terms of the illuminance
or luminance intensity which is expressed in lux. And similarly this when reflected from any
object, the light in the perpendicular direction is what we call to the plane perpendicular
to the light rays is what we call brightness which is again mentioned in terms of a food
candles. So having done so much, we look at what should
comprise an illumination system. The illumination system therefore comprises
of three major things. One is the lamp which is the source, artificial
source of light which could be using one of the four physical processes that we have studied. It could be using incandescence in the case
of an incandescent lamp, it could be using electroluminescence in the case of a discharge
lamp, fluorescence in case of a fluorescent lamp and two the control gear, three the luminaires. What comprises of the control gear? If you look at the crude sense you need something
to hold the lamp and direct the light out of this lamp on to the object of interest. Now the fixture which holds the lamp and its
position or it helps in mounting the lamp is what we can call as luminaire and luminaire
itself to some extent with the help of the reflecting coating put inside the luminaire
which in a colloquial term can be called as shade, we have lamps at home which have shades. They basically direct the light, we normally
put them in most, if the ceiling height is very high like the old building, older buildings
we would have the light directed downwards otherwise in the modern structures where the
ceiling heights are lower, we direct the light upwards to the room which gets reflected and
is incident on the object. So luminaires not only that means provide
support and they also enable electrical connection to lamp or lamps it connect. That means it is a shade or a fixture which
gives the physical support and remember all these lamps are being run using electrical
power, so there must be connections provided by a way of leads in and leads out. Now we also saw that in case of a discharge
lamps, the radiation is by virtue of a gas discharge in the vapor or metal vapor or a
gas which is ionized that means there is an electric field. And once electric field discharge takes place
there is an arc which is nearly constant current. That means there is a requirement to have
a initially higher voltage for the arc to strike and later on it needs to maintain the
current. And therefore that calls for certain accessories
that is what we call as a control gear and luminaire may have provision to include those
things within its container. Now therefore primarily it provide support
and enables electrical connections. It says lamps, all lamps that means in a single
luminaire I may be having more number of lamps. One could in fact look at the required amount
of illuminance on the object sources and there by work out how many lamps are required and
accordingly put. These are part it controls, controls means
it sees in which direction the light has to go. Imagine a naked bulb mounted on the wall,
the light would go in all directions and if the walls and ceiling are not properly maintained,
it may so happen that good amount of light may be absorbed by the walls and only a small
portion of the light is received on the tough surface which is there is a wastage of light. Other thing is it distributes light, in fact
the distribution of light over certain restricted zones are having what we call beam spreads
or beam angles. We find these have applications in automobile
lighting and also in sports lighting. Remember in these kind of applications, depending
on the size of the object, sports lighting when we talk of it is the outdoor games and
depending on the type of the game athletics is another cup of tea in the sense athletics
one may not have to observe a small object that is if you say a game like badminton,
a shuttlecock is a smaller object. So recall from the way eye functions, finer
it is more illumination is required that means you need your phobia to come into activity
and these are the reasons which, so that is why we say luminaire helps in distributing
where it is required that directs the light. Of course, obviously control and direct are
synonymous with one another in this context but at the same time one has to see that temperatures
are kept within prescribed limits. We do not want any undue temperature rise. The issue is very simple, if you use incandescent
lamps they are essentially depending on the material or the filament being maintained
at a certain temperature, higher the temperature better is the radiation. We have seen it is proportional to the fourth
power of temperature. Now it has got a direct bearing on the overall
design of your electrical system in the sense that the lighting has to be integrated with
the ventilation and air conditioning system because together will decide an overall electrical
low requirement. And today the scenario is we should look for
as many measures as possible in trying to reduce the energy. This apart, one has to look at the ease of
installation and maintenance. Installation because invariably the sources
are kept at a height, so it should be possible to install with minimum of complexity. Second thing maintenance, remember the luminaire
depending on the type of environment, let us say we talk of street lights, they have
to get to the vagaries of weather that is there can be storms, rains. So any dust deposition on the glass enveloped
lamp would make the envelope opaque and thereby reduce the light output and it may be depending
on the height, it may be possible to periodically clean or may not be possible. So these are the issues which have to be kept
and more the number of loose particles, it becomes more difficult to maintain. At the same time in order to function well
and have good psychological impact esthetics has to be kept in mind. In fact it is said unless a lamp itself is
an antique piece, it should not draw any attention to itself, the attention should be drawn to
the object of interest. Let’s say we are in a display room where
we have a model to be displayed then the way the light is directed and controlled and the
luminaires are located, it should see that all the light is received on the model being
displayed, unless the model itself is a luminaire and in that case it’s fine it can. And the cost cannot be ignored as we have
being saying from the beginning economics plays quite a good amount of impact and it
should be viable and in fact this the installation and maintenance together with the economics
are highly interlinked and all systems should be economically viable. The lighting could be commercial or it could
be general. Now most of the times commercial lighting
when we talk about luminaires, we have depending on the application. Let’s say in a show case the requirement
is to show certain products. So their requirements could be different but
in general office or interior lighting we normally have fluorescent lamps. Fluorescent lamps could be one or more and
typically they are mounted at a height of 5 to 6 meters whereas these fluorescent lamps
as all of us are familiar in our residences and hostels, we have fully exposed batten,
they are simply mounted on a batten with the two enhold lamp holders I mean the enholders
and whereas it could be an enclosed multi lamp kind which is called ventilated with
reflectors. These reflectors could be mirrors and that
is the other. The issue is there it could be difference
in control which depends on the luminous intensity of the lamps employed and how one wants to
distribute the light and the number of lamps that are involved. Here let us recall what we learnt in loss
of illumination. If we consider an incandescent lamp, we find
the radiation or the due to point source at any point on the task surface can be related
to I over d square where d is the distance between the point and that is point of observation
and point of source which means it keeps on varying inversely with square of the distance. So if we use incandescent lamps this has to
be borne in mind. One aspect which I must mention is that in
designing over the entire task area, we try to maintain nearly same level of illuminance
that is the lux levels with hardly difference over any point less than 30% okay. So that being kept, we need to locate the
lamps accordingly and you can. On the other hand if we have as against a
point source a line source, a typical example of a line source is a tube light or a fluorescent
lamp we find it is the distance between the point of observation and is inversely with
the distance. Now imagine you can get the similar structure
by having number of incandescent lamps placed one after the other over a vertical, over
a length of a line. And as against this supposing we create what
we call a sheet of light or a plane source radiation. In fact we see large conference rooms and
large work rooms where discussions are to be held, one tries to create a sheet of light
over the task area. This is very much true of a conference room
where you have a large oblong table and you have on top of the table. See the distinct advantage is that when you
try to create using set of lamps, luminaires so design that you get a sheet of light. How do we have achieved this? Now we have a luminaire that means luminaire
is nothing but a physical support which is similar to our shade which in case of a incandescent
lamp has got a conical structure. Now that has a reflecting coating or a mirror
is placed and then the number of lamps are fixed below which a diffuser is placed. Once you have a diffusing exterior envelope,
the entire light gets diffused and forms a sheet of light. So you may be having let’s say over certain
area, number of fluorescent lamps included within this luminaire. Now designer should always aim at locating
lamps on this. So with the help of reflectors and there are
what are called louvers with openings. See you can have diffusers, you can have louvers
commonly what we find a louvers with slanted fins or vanes this is being used. So control direct and reflect and as a result
we try to see that as much of the light flux that comes from the source is allowed to fall
on the object of interest. If we take a simple batten type of a fluorescent
lamp, there is virtually no control, light goes out in all directions and whatever comes
below or on the task that is what is available for the task. The next most common thing is enameled reflectors. I told you even the simplest of the luminaires
which we talked call as lamp shades are nothing but enamel coated metal conical reflectors. The next best would be to have mirror reflectors
and you could have louver type of shields at the bottom. Basically the two purposes which a shield
does is which enables which prevents any dust entering and also acts as an opening for the
enclosed lamp assembly for the light to go out and you could be using opalescent shades
that is it gives an opaque nature that is a diffusing shade which will enable. Now the principle to be borne in mind is this,
if we had a point source depending on the distance the light available on the task varies
inversely as the square of the distance that means there is a barring to the mounting height. There is an optimal mounting height if you
are using point sources and it varies as square. As against this if we use fluorescent lamps
which can be thought of as a line sources, the mounting height dependency is there but
is inversely proportional to the mounting height. On the other hand with the help of various
luminaires along with the diffusing shades, it is possible that we get nearly plane source
of radiation or a sheet of light which is independent of the mounting height. That’s what we look for especially in office
lighting because and the reflectors enable and of course as I told you depending on certain
applications we can orient it in a desired solid angle. The louvers themselves could be having the
square mesh or a diamond mesh or thin layers, this depends on the type of luminaires you
have. They could be the issue is again what one
uses depends on the ease of maintenance and some knowledge of the local conditions becomes
very important. Now all this holds good essentially for what
we call office lighting or interior lighting. We have one other category where it is very
important is the industrial lighting and the street lighting where normally the mounting
heights are reasonably high number one, number two they are prone to more what you call vagaries
of weather, three what we look for is that in those applications, it is not necessary
to really go into fine details or be able to reproduce the colors or meaning to say
that have good colour rendering and that is where one may not really bother so much. So there are two kinds of a luminaire shown
here. The top one shows see this could it shown
it could be viewed as a fluorescent lamp the circle did denoting that with the pure reflector,
the other one with a louver placed below which is being shown in the form of a square mesh. Now in addition to this, we will observe that
these luminaires will have what are called as certain ventilating mechanisms. So that the heat does not build up and temperatures
do not rise unnecessarily because remember no matter what type of source you use, there
is some amount of heating involved. In fact we saw the discharge lamps could be
using either cold cathode or hot cathode. Cold cathode would need higher voltages as
against hot cathode lamps. Now these are either recessed in the ceiling
or mounted on the surface. When they are mounted on a surface these are
the two issues otherwise since normally unless if you are trying to create a sheet of light
it depend on the mounting height. So they could be suspended, when you will
suspend they are called down lights, okay. The other application therefore I was telling
you the air handling becomes very important ventilation. So it shows three different ways of allowing
the air handling. The top could be having slots cut as shown
in figure to the left most, this particular type of luminaire having this is called plenum
or you could be having ducts as a single duct and twin duct type of air handling. That is you can have air going in and coming
out so that the temperature of the luminaire does not rise very high. Now the issue comes how does one express the
efficacy of these luminaires. There is one factor which we call as the light
output ratio. This is defined as light output with luminaires
by sum of the individual light output without luminaires. Obviously when you talk of such an index it
should be very clear to the user where he is talking of depending on the task. This is abbreviated as LOR and normally when
we talk of LOR, it includes both downward as well as upward light but normally downward
light is important, bearing in mind most of the lamps are mounted either in the reassess
or suspended from the roof or on the surface of the walls and we are either sitting at
a table and working or on the floor. So therefore when you are looking at the luminaire,
you look at the DLOR that is the index which is of importance. Now remember if we direct the light upwards
it illuminates indirectly by reflections. The advantage of that is at no point there
can be a glare, we defined glare. Glare is the effect of intense light in the
line of vision and this has to be avoided because this effects our ability of the human
eye to adjust. Human eye has got a very good adjusting ability. Now if we use plane enamel reflectors, the
LOR could be lower if you want to improve you can use mirrors. In fact if you see the modern day luminaires
especially meant for large complex office lighting or industrial lighting and even the
street lighting luminaires they come with mirror reflectors, keeping glare into consideration. The next issue which I said is industrial
luminaires. Now depending on the height, essentially it
depends on the height. Height of an industrial bay depends on the
type of manufacturing process and the volume of the material that they have to handle. Now therefore the industrial interiors reaching
up to about 6 meters they can be lit using fluorescent lamps with matt white reflectors. Again the idea is the maintenance difficulties
are much more in an industrial environment. Environment is more hazardous and more scope
for pollution and that’s the reason why you do not go in for really sophisticated
systems whereas what we call high bay luminaires are used whenever there is height beyond 6
meters and there invariably it is the discharge lamps. We have already mentioned discharge lamps
are used on two accounts, one because they operate with high luminous efficacy that’s
the most important thing. There is no doubt colour rendering is bad,
in case of a mercury it is better but in case of a sodium vapor which is predominantly used
again between sodium and mercury, the choice of sodium has come because of a high utilization
ratio. Luminaires in hazardous areas need special
requirements, there could be it should be encapsulated and there should be pressure
resistant and they should be very sturdy. Normally they have a steel or a cast iron
exterior housing and the so design that they can prevent any explosion what so ever and
therefore depending on the, there are certain categories of explosive areas have been identified
a card zone 0 is 1 where there is a scope for explosion all the time. Zone 1 which is normally explosive not all
the time, zone 2 if it is abnormally explosive that is it is as though there is some finite
chance. Let us look at it this way, I can say may
be about 10% of the times, zone 2 is explosive more than 60, 70% of the times zone 1, 100%
of the time is zone 0. That’s how accordingly luminaires have to
be designed to encapsulate that there is no ingress of any poisonous gas into, remember
this is at a high temperature, filaments are at high temperature there could be a discharge. So any poisonous explosive gas getting in
can create an explosion. Moisture and dust of course can be handled
by having gaskets. See luminaire has a glass enveloped through
which a light is coming out, this is should be gasket. See inside the house one may have open luminaires
with just fins. The other important area where one requires
completely shield luminaires are in the shower or laundry where water is used. Now the other categorization of lighting needs
to be done before we look at these illuminance systems. One is emergency lighting, you need certain
minimum lighting even when the normal lighting fails so that you are able to move around
and take care of your basic activities without any unsafe accidents. This is what we call emergency lighting and
then that is a lighting which we tried to provide in circulation areas, in fact the
usage of 5 watt lamps at home as night lamps or bed lamps is essentially to see that we
have. Now there it’s not an emergency lighting it
is what we can categorizes as safety lighting or in fact we see escape lighting is what
is mentioned here. Escape lighting is a minimum lighting to be
able to locate the exit passages. In fact we have observed these that these
exit passages are often provided by guided lights or fluorescent lights or indicators
in fact. Safety lighting is normally not less than
the 5% of the normal lighting in potentially hazardous areas that is very important. So there is scope in certain areas where one
may meet with an accident and in those areas, one has to see that it is never below 5% of
them. Let us say we need about say 20, 30 lux in
the normal operation, the general lighting requirement in an interior. So it should not be below 3 lux so that you
will in the hazardous areas. This apart, we do have stand by for activation
of vital implements and permanent separate self-supporting power system. This becomes part of your requirement from
the utility. So all this emergency lighting requires that
there is a self-supporting power system. We will look into that and those why we are
looking at it at this point of time is that sometimes these days the luminaires themselves
are provided with reliable batteries which are mains rechargeable, they act as a stand
by supply, this is provided. The other issue is you have switching on some
power to emergency generator or a battery supply. So all this the utility system designer can
low. So you see lighting itself has to be there. There is a certain functional lighting, this
is an emergency lighting because in the event of an emergency you need and there is certain
basic lighting from the safety point of view. All this has to be assured and now coming
to the road lighting, there are various ways you have column of lights that is you have
lamps placed mounted on the poles on one side of the road or either side of the road across. Now supposing if there are some walls, you
mount them on the walls or you have it as a form of a catenary on the middle of the
road suspended by the two poles on the either side. The important is that you have a plane of
symmetry in the vertical plane which is perpendicular to the access of the road along the road that’s
the important. This applies to street lighting or highway
lighting. As I was telling you that there could be a
column or a span on either side or both sides or a catenary, these are the ways to do this. Now this shows a picture of a reflecting luminaire. Now since here we are showing it for a road
lighting application which is completely enclosed because it is subject to vagaries of the weather. The circle denotes your lamp, there is a reflector
or the luminaire per say and then the enclosure which could have a, bottom could be glass
and in order to see that dust or moisture does not get in we will have a gaskets provided. This is a refracting in the sense that the
outer envelope will not be transparent glass but it is an opaque thing so that if the light
diffuses it comes. This may not be suitable as a normal street
light but it is an ornamental lighting of path ways and paths can be which when it is
made at low heights where the light falls in the sight of vision and hence avoids glaring. This is both reflecting as well as diffusing. This shows a typical luminaire used in what
we call post top lanterns, you can see the circle depicts the lamp and the triangular
thing is the reflector. The overall egg shape dome is there which
is translucent opaque thing which diffuses. So you have reflecting, refracting and diffusing
kind of a thing. Now the difference between the interior luminaires,
industrial luminaires and the exterior luminaires is that the luminaires in industrial environment
and the external environment need to have taken care of dust and moisture ingress. Therefore they are used with corrosion resistant
sturdy materials and they are completely enclosed. Flood lights is another application which
in fact is what is used especially in sports lighting, they have rain proof holder with
wide or narrow beam reflectors. This beam depends on the application. When they are used for certain narrow zone,
it will have a narrow beam. They are invariably a very high wattage incandescent
lamps or halogen lamps. The halogen lamps we said are nothing but
using certain metal halides, it only improves the life of an incandescent lamp because it
avoids blackening which is prevalent with your normal incandescent lamps. High pressure mercury vapor lamps are also
used for flood lighting and these days even low pressure sodium vapor lamps. Spot lights or down lights these are used
essentially for studios and performances and this they used along with screens, reflectors
and you know in theaters one needs to create different colors, so one can use filters colored
envelopes and closed lamps. Now the issue is their control is involved
essentially they are all electrical accessories. The outer screen can be controlled with the
help of motors and down lights or spot lights are essentially suspended from the top. So in effect one could look at the summary
of the lecture on illumination systems as that illumination system comprises of a lamp
that is the artificial source of light luminaires and the control gear. Now here there are certain control gears such
as the ballast, starters in case of the discharge lamps and fluorescent lamps and certain applications
like street lighting can have varying levels of intensity depending on the time of the
day. For all this will be covered in the subsequent
lesson. Commercial luminaires can be categorized as
general and industrial. And luminaires are characterized but the way
they control and direct the light which depends on the intensity distribution and number of
lamps. The difference is depending on the application
although at home a single luminaire may have only one lamp. Most general applications have more than one
lamp and the three basic issues are one luminaire which supports with a reflector which reflects
directs a light towards where it is to be and depending on the environment either it
is enclosed or has louver through which light comes on to the task surface. Use of mirrors to be avoided but if used along
with diffuses is fine. Now the efficiency of a luminaire is talked
in terms of the light output ratio which we defined as the light output with luminaire
to the sum total of the light output of the system without luminaire. Normally downward luminaire is downward light
output ratio is of importance because most lamps are mounted at a height and the task
is at the table of required thing. For hazardous areas one has to be very careful
that they maintain temperature, so they have to be sturdy and encapsulated to resist any
pressure variations. And wherever moisture is involved gasket should
be provided and completely shield so that dust or moisture does not take place. Now for the sake of having different emergency
lighting or safety lighting, one should have self-supporting power system when normal lighting
fails. This could be in the form of a rechargeable
batteries provided within the luminaire. The questions that may be address which type
of lighting are used for general lighting and why? What are louvers? What are the different luminaires considered
placement wise? What type of lighting is used in industrial
lighting systems? What are the different types of emergency
lighting used? Answer to questions of certain questions in
the previous lecture are why can’t an incandescent lamp be used as a standard lamp. Due to the aging factor the light output of
an incandescent lamp decreases with use. What is a utilization factor? It gives the index of light reflected from
a luminaire. What is a maintenance factor of a luminaire? It is the depreciation of light output of
the luminaire due to accumulation of dust and moisture and age. Advantage of using diffusing type of luminaire? They avoid glare. Thank you.

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