Install lighting systems

Light

Light is defined as electromagnetic radiation or energy transmitted through space or a material medium in the form of electromagnetic waves.

The electromagnetic spectrum covers an extremely broad range of radiation, ranging from radio waves with wavelengths of many metres, spanning several orders of magnitude, down to X-rays with wavelengths of less than a billionth of a metre.

The electromagnetic spectrum

The range of the electromagnetic spectrum from 380 to 780 nm is called light.

The main units used to describe light and its effects are :

1. Luminous flux2. Luminous intensity3. Luminance4. Illuminance

The flow of light or luminous flux ( ) is the light energy radiated out per second from a body in the form of luminous light waves.

Its unit is the lumen ( lm ) .

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Luminous flux from a lamp

Luminous flux of some typical light sources

The power of a source of light is known as its luminous intensity

Luminous intensity measures flux in a given direction.

Luminous intensity

- It is abbreviated as I . - Its unit of measurement is the candela (cd )

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Some typical luminous intensities

Luminance indicates the lightness of an emitting surface ( e.g Sun, moon, candle ) for an observer.

- It is abbreviated as L . - Its unit is the candela per square metre (cd m ˉ ²).

Luminance of some light sources (in cd/m²)

Illuminance ( E ) is the light falling on a surface.

It is measured in terms of luminuous flux received on unit area, i.e lumens per square metre ( lm/m 2 ) .

Its unit is the Lux.

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Some typical illuminances

Schematic of the most important lighting terms

Illustration of the Four main units

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In any light phenomenon, it can be observed that the light originating from an emitting source expands through space. As it moves away from its source, the illuminance that it produces on a surface decreases by the square of the distance.

Equally, if the surface is not orthogonal to the incident beam, the illuminance decreases by the cosine of the angle of deviation, resulting in the following:

4.1 State the following factors relating to illuminance :-(i) Illumination law.(ii) Inverse square law(iii) Cosine law

( i ) Illumination law.

Illumination ( E ) is directly proportional to the luminous intensity ( I ) of the source of light.

E I

( ii ) Inverse square law

The illumination of a surface is inversely proportional to the square of the distance (d) of the surface from the source.

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E I / d 2

The surfaces A1 and A2 both cover the same solid angle from the light source. Because light travels in straight lines, they both intercept the same luminous flux.

However, since their areas are different, the illuminance that this flux produces on the surfaces is not the same. The illuminance depends on the area on to which the light is falling; it is proportional to the inverse of the distance to the source squared.

( iii ) Cosine law

Illumination ( E ) is directly proportional to the cosine of the angle made by the normal to the illuminated surface with the direction of the incident flux.

E I cos / D 2

4.2 Explain the meaning of the term photo bench.

A photo bench is an instrument used to compare the light intensities of two lamps.The lamps are supported on an optical bench fitted with a ruler.A photometer head is mounted between the lamps ( Is & Ix ) so that its position can be varied until its two

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sides are equally bright. The distances ( ds & dx ) of the lamps from the photometer are noted. The location of the photometer is adjusted until the illumination on its two faces is judged to be equal. Then,

Intensity of standard lamp – Is ( cd ) = Intensity of test lamp – Ix ( cd ) ds 2 dx 2

4.3 State the use of illumination meter / luxmeter

An illumination meter is used to measure the amount of light ( lux ) falling on an object.

A simple way of measuring the luminance is to use a photocell with a special shading rod.

4.4 Describe the operation of the following:

(i) fluorescent tubes with an autotransformer and no starter switch(ii) fluorescent tube with electronic ballast(iii) high pressure mercury-vapour discharge lamps

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(iv) high and low pressure sodium vapour discharge lamps(v) halogen lamps(vi) energy savings lamps

Types of lamps

1. Incandescent lamps

- Regular lamps- Tungsten halogen lamps

2. Gas discharge lamps

- Low pressure fluorescent lamps- Low pressure compact fluorescent lamps- Low pressure sodium lamps- High pressure mercury vapour (MV) lamps- High pressure metal halide lamps- High pressure sodium lamps

3. Electro-luminescent radiation lamps

- Light emitting diode ( LED ) lamps

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Fluorescent Lamps

Fluorescent lamps are the most commonly used commercial light as they have :

relatively high efficacy

good diffuse light distribution characteristics

long operating life.

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A fluorescent tube consists of a glass tube with the following features:

filled with an argon or argon-krypton gas and a small amount of mercury coated on the inside with phosphors equipped with an electrode at both ends

Fluorescent lamps provide light by the following process :

- An electric discharge (current) is maintained between the electrodes.

- This current excites the mercury atoms, causing them to emit non-visible ultraviolet (UV) radiation.

- This UV radiation is converted into visible light by the phosphors lining the tube.

All fluorescent lamps require a ballast to provide correct starting voltage and to regulate the operating current after the lamp has started.

Types of Fluorescent Lamps

a. Preheat lamps

b. Instant start lamps

c. Rapid start lamps

Preheat Fluorescent Lamps

- The cathodes of the lamp are preheated electrically for a few seconds before a high voltage is applied to start the lamp.

- The preheating is accomplished by the use of an automatic switch, called a “starter”, which applies current to the cathodes for sufficient time to heat them.

- Preheat lamps operate normally in a preheat circuit (preheat electrodes, ballast, starter, lamp and lamp holders).

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Instant Start Fluorescent Lamps

- The instant start lamp requires a high starting voltage, which is supplied by the ballast.

- Since there is no preheating of the cathodes, there is no need for a starter.- Electrode heating is provided by the arc once it has been established.- Instant start lamps operate normally only in an instant start circuit

(instant start ballast, lamp and lamp holders).

Rapid Start Fluorescent Lamps

- The ballast quickly heats the cathodes causing sufficient ionization in the lamp for the arc to strike.

- Rapid start lamps start almost instantly (in one or two seconds).- No starter is required – eliminating the time delay of preheat systems.

Fluorescent tubes with an autotransformer and no starter switchA fluorescent lamp not using a starter switch is commercially known as an “instant-start’ or “quick-start’ type.

As shown in the following drawing, the normal starter is replaced by a filament heating transformer whose secondaries SS heat up the lamp electrodes A and B to incandescence in a fraction of a second.

This combination of pre-heating and application of full supply voltage across lamp electrodes A and B is sufficient to start ionization in the neighbourhood of the electrodes which further spreads to the whole tube.

An earthed strip E is used to ensure satisfactory starting.

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The advantages of a startless fluorescent lamp method are :

- It is almost instantaneous starting- There is no flickering and no false starts.- It can start and operate at low voltage of 160-180 V.- Its maintenance cost is lower due to the elimination of any starter-

switch replacements.- It lengthens the life of the fluorescent tube.

Fluorescent lamp with electronic ballast

Fluorescent lamps require a ballast to apply starting voltage to the lamp and establish current flow – an "arc" – between the lamp electrodes.

Once the lamp is operating, the ballast regulates the lamp current and power.

The two types of ballast available are the magnet and electronic ballasts.

Magnetic Ballast

A simple device that uses a magnetic core and coil assembly transformer to perform the minimum functions required to start and operate a lamp.

Measured lamp voltage and current waveforms for magnetic ballast

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Electronic Ballast

A  complex device that substitutes electronic components for the core and coil assemblies found in magnetic ballasts. Electronic ballasts are significantly smaller, lighter and quieter than their magnetic counterparts. Also, it offers distinct advantages in energy efficiency and lamp operation.

Measured lamp voltage and current waveforms for an electronic ballast

The advantages of an electronic ballast as compared to a normal ballast are as follows :

1. It doesn’t produce any noise and doesn’t blink also.

2. It doesn’t consume more electric power. It saves 33% of electric power.

3. It doesn’t require a ballast and a capacitor.

4. It starts to emit light in less than 1 second.

5. Its weight is low.

6. It can work on voltage between 100 and 300 volts.

7. It doesn’t get hot.

8. Its life is double.

9. It can work on either a.c. or d.c. source.

10. It gives more light (66 lux per watt) than tubes with normal magnetic ballast.

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High pressure mercury-vapour discharge lamps

A mercury-vapor lamp is a gas discharge lamp which uses mercury in an excited state to produce light.

The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger bulb which provides thermal insulation and protection from ultraviolet radiation.

Mercury-vapor discharge lampWhen a mercury vapor lamp is first turned on, it will produce a dark blue glow because only a small amount of the mercury is ionized and the gas pressure in the arc tube is very low.

As the main arc strikes and the gas heats up and increases in pressure,the light shifts into the visible range and the high gas pressure causes the mercury emission bands to broaden somewhat, producing a light that appears more-white to the human eye. Even at full intensity, the light from a mercury vapor lamp with no phosphors is distinctly bluish in color.

If the discharge should be interupted (e.g. by interuption of the electric supply), it is not possible for the lamp to restrike until the bulb cools enough for the pressure to fall considerably.

Mercury vapor lamps rarely burn out completely but suffer from lumen depreciation and the bulb produces 50% less light output every five years, to the point of becoming ineffective while still drawing the same amount of power they drew when they were new.

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Low pressure sodium vapour discharge lamp

A low pressure sodium vapor lamp is a gas discharge lamp which uses sodium in an excited state to produce light.

Low pressure sodium (LPS) lamps, also known as sodium oxide (SOX) lamps, consist of an outer vacuum envelope of glass coated with an infrared reflecting layer of a semiconductor material that allows the visible light wavelengths out and keeps the infrared (heat) back.

It has two inner glass U-pipes that hold solid sodium and a small amount of neon and argon gas mixture to start the gas discharge, so when the lamp is turned on it emits a dim red/pink light to warm the sodium metal and within a few minutes it turns into the common bright orange color as the sodium metal vaporizes.

LPS lamps are the most efficient electrically-powered light source. As a result they are widely used for outdoor lighting such as street lights and security lighting where color rendition is viewed by many to be less important. LPS lamps are available with power ratings from 10 W up to 180 W.

Another unique property of LPS lamps is that, unlike other lamp types, they do not decline in lumen output with age. LPS lamps, however, do increase energy usage slightly (about 10%) towards their end of life, which is usually rated around 18,000 hours for modern lamps.

LPS lamp failure does not result in cycling; rather, the lamp will simply not strike, and will maintain its dull red glow exhibited during the start up phase.

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High pressure sodium vapour discharge lamp

High pressure sodium (HPS) lamps are smaller than LPS and contain additional elements such as mercury, and produce a dark pink glow when first struck, and a pinkish orange light when warmed.

High pressure sodium lamps are quite efficient (100 lm/W). They are used for outdoor lighting such as streetlights and security lighting.

The lamp is powered by an AC voltage source in series with an inductive "ballast" in order to supply a nearly constant current to the lamp, rather than a constant voltage, thus assuring stable operation.

HPS lamps can be started at a relatively low voltage but as they heat up during operation, the internal gas pressure within the arc tube rises and more and more voltage is required to maintain the arc discharge.

At the end of life, high-pressure sodium lamps exhibit a phenomenon known as cycling, which is caused by a loss of sodium in the arc. When a lamp gets older, the maintaining voltage for the arc eventually rises to exceed the voltage provided by the electrical ballast.

As the lamp heats to this point, the arc fails and the lamp goes out. Eventually, with the arc extinguished, the lamp cools down again, the gas pressure in the arc tube is reduced, and the ballast can once again cause the arc to strike. The effect of this is that the lamp glows for a while and then goes out, repeatedly.

Halogen lamps

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In ordinary incandescent lamps, the filament made of tungsten is mostly deposited on the bulb. A halogen lamp is an incandescent lamp in which a tungsten filament is sealed into a compact transparent envelope filled with an inert gas, plus a small amount of halogen such as iodine or bromine.

The halogen cycle increases the lifetime of the bulb and prevents its darkening by redepositing tungsten from the inside of the bulb back onto the filament.The function of the halogen is to set up a reversible chemical reaction with the tungsten evaporating from the filament.

The regeneration cycle that occurs between the halogen and tungsten atoms is the key to the bulb's long life and its superior lumen maintenance.

Halogen lamps get hotter than regular incandescent lamps because the heat is concentrated on a smaller envelope surface, and because the surface is closer to the filament. This high temperature is essential to their operation. Because the halogen lamp operates at very high temperatures, it can pose fire and burn hazards.

Energy savings lamps

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Compact fluorescent (CF) lamps are commonly known as energy savings lamps.

Compact fluorescent lamps have some benefits in comparison with classic lamps. It consumes lower power ( 80%) and has a longer lifetime (5 to 15 times). The long life of CF lamps means that maintenance costs can be much lower than for incandescent lighting. A single CF lamp can save enough electricity (coal-fired) to keep a ton of carbon dioxide out of the atmosphere.

A compact fluorescent lamp consists of a gas-filled glass tube with two electrodes mounted in an end cap. It contains a low-pressure mix of argon gas, mercury vapor, and liquid mercury and is coated on the inside with phosphors. Lamps can be of varying shapes, sizes, power output, lumen outputs, and colours.

When the CF lamp is first turned on, the mains voltage across it is not sufficient to

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cause the initial ionization of the vapour. A starting element is thus needed to provide a high voltage pulse across the tube to start the process.

A current limiter, known as a ballast, must be added to prevent the current increasing to a level where the lamp is destroyed. The ballast controls the current and voltage flowing into the assembly and it may be attached directly to the lamp, or may be remotely connected.

Electronic ballasts replace the starting and inductive elements of the conventional system. The aim of using an electronic ballast is to increase the operating mains frequency of 50 Hz to over 20 kHz .

The two main effects when using an electronic ballast are :

a) The gas in the tube does not have time to deionise between current cycles, which leads to lower power consumption (typically about 70% of that with conventional ballast), longer tube life and almost no flicker.

b) The inductor required to generate a large enough overvoltage to ionise the tube is smaller, and so generates less resistive losses, and the weight of the system is reduced.

However, the electronic solution is more complex and has a higher initial cost – although this will eventually be paid back by the savings in energy.

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4.5 Explain the term stroboscopic effect.

When fluorescent lamps are operated on ac circuits, the light output creates cyclic pulsations as the current passes through zero. This reduction in light output produces a flicker that is not usually noticeable at frequencies of 50 hertz, but may cause unpleasant stroboscopic effects when moving objects are viewed.

This cyclic flicker can be minimized by :

Connecting fluorescent lamps to a three phase system in an industrial installation

using a three-lamp fixture and connecting each lamp to a different phase of a three-phase system.

4.6 State the basic factors to be considered for designing a lighting installation.

The basic factors to be considered for designing a lighting installation are :

a) Architectural features of a building that can affect lighting.

b) Reflectance, diffusion and absorption of light by ceilings, walls, floor and furnishings.

c) Dimensions of space to be illuminated : ceiling heights and floor area.

d) Proper selection of luminaries by evaluating their light distribution, efficiency, decorative value, elimination of glare and economy.

e) Height and spacing of luminaries within a room based on room function.

A well designed lighting installation is one that

Provides adequate illumination for a particular set up

Avoids glare and hard shadows

Provides sufficiently uniform distribution of light all over the working plane.

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4.7 Describe the operation of high-voltage signs and state the importance of firemen’s switch.

The voltages at which H V signs operate are between 600 V and 5000 V.Thus, a 10 kV display unit could be used provided its supply transformer is centre-tapped to earth. Where the input exceeds 500 W, means are to be provided for automatic supply disconnection in the event of a short –circuit or earth leakage current which exceeds 20 % of the normal steady current.

High-voltage discharge lamps are generally supplied by double-wound transformers and auto-transformers may be used on two – wire circuits which do not exceed 1.5 KV measured on open circuit.

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All equipment are to be enclosed in an earthed metal or substantial container suitable for high voltage. A notice “ Danger – High Voltage ” is to be permanently fixed near the equipment.

Isolation of live conductors may be made by either one of the following methods:-

An interlock on self-contained fitting to be provided in addition to the switch normally used for controlling the circuit.

Local isolation by plug and socket or similar method in addition to normal control switch.

Switch with removable handle.Alternatively, a switch of a type that can be locked may be fitted if the keys are under the custody of authorised persons.

Importance of firemen’s switch

A fireman’s emergency switch is required for all exterior installations and unattended interior installations where they are used for window display lighting.

The switch must be:- Capable of isolating all live conductors Coloured red and marked FIREMAN’S SWITCH. Clearly marked ON and OFF with the off position at the top Installed in a conspicuous position Reasonably accessible to firemen.

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4.8 State the importance of emergency lighting.

Emergency lighting is essential for the safety of building occupants. It is vital that the lighting comes on if the normal lighting fails.

It needs to be sufficiently bright, illuminated for a sufficient length of time and the light sources so positioned, that the building occupants can be evacuated safely in an emergency.Escape lighting is part of the emergency lighting which is provided to ensure that the means of escape can be safely and effectively used at all material times.

The function of escape lighting is to :-

Indicate clearly and unambiguously the escape routes.

Provide illumination along such routes to allow safe movement towards and through the exits provided.

Ensure that fire alarm call points and fire fighting equipment provided along escape routes can be readily located.

Escape lighting luminaries should be located near each exit door and emergency exit door and also at points where it is necessary to emphasize the position of potential hazards, for example:

1. near each intersection of corridors2. near each change of direction ( other than on a staircase )3. near each staircase so that each flight of stairs receives direct light4. near any other change of floor level which may constitute a hazard5. outside each final exit and close to it

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(a) Emergency Lighting

(b) Open Area Lighting

(c) Other Areas (eg lifts)

(d) Signage

(e) Maintained or Non-Maintained - Duration of Luminaires (1 hr minimum)

(f) Escape Route Lighting - Fire Points

(g) Wiring

(h) Central System

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4.9 List the IEE regulations concerning industrial and commercial lighting circuits.

1. Where conductors or flexible cables enter a luminaire, the conductors should be able to withstand any heat likely to be encountered or sleeved with heat resistant sleeving.

2. A ceiling rose, unless designed for the purpose, should have only one flexible cord.

3. The flexible cord used to make a pendant ( the ceiling rose, flex and lampholder assembly ) should be capable of withstanding any heat that is likely to be present in normal use.

4. Where a flexible cord supports or partly supports a luminaire, the maximum mass supported shall not exceed the values as stated in the Regulations.

5. A ceiling rose shall not be used on a voltage exceeding 250 V.

6. Parts of lampholders, installed within 2.5 m of a fixed bath or shower, shall be constructed or shrouded in insulating material.

7. Lighting switches shall be installed, so as to be normally inaccessible to persons using a bath or shower. The regulation does not apply to ceiling switches operated by an insulated cord.

8. For circuits supplying equipment in a room containing a fixed bath or shower that can be touched at the same time as conductive parts, the protective device shall disconnect the circuit within 0.4 second.

9. For circuits on TN or TT systems, where an Edison screw lampholder is being used, the outer contact shall be connected to the neutral conductor.

10. Final circuits for discharge lighting (including Fluorescent luminaries) shall be capable of carrying the total steady current.

4.10 List the types of luminaires for.:

(i) Decorative luminaires for indoors and outdoors(ii) Flood lights(iii) Road lighting(iv) Industrial lighting

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Decorative luminaires for indoor and outdoor utilizations

( a ) Indoor luminaire

Pendant including incandescent lamp Chandelier including incandescent lamps Halogen lamp

( b ) Outdoor luminaire

Neon gas lamp Sodium vapour lamp Mercury vapour lamp

Luminaire for flood lights

Halogen lamp Mercury vapour lamp Sodium lamp

Luminaire for road lighting

Sodium lamp Mercury vapour lamp Fluorescent lamp

Luminaire for industrial lighting

Halogen lamp Fluorescent lamp Incandescent lamp Mercury vapour lamp Sodium vapour lamp

4.11 State the use of indicating lamps.

Indicating lamps are used in industrial panels to provide information about the status of a process.

Two types of indicating lamps available are as follows : Incandescent type Neon type

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