22 FACTORS INFLUENCING REQUIREMENTS OF LIGHT
P.G. Padma Gowri
Introduction:
Lighting is an essential part of any buildings. Apart from its aesthetic and decorative aspects, good lighting has a strictly utilitarian value in reducing accidents, increasing the output of factory and other workers and improving the general health o the community due to reduction of eye-strain. The science of illuminating engineering is therefore becoming of major importance.
Objectives:
· To understand the nature of light.
· Explanation Impart about of various artificial lighting sources.
· Design of lighting system.
· Placement of effective lighting for buildings.
We got solar lighting during day time (natural lighting). To get sunlight windows, doors, ventilators etc. will be placed in proper size and place. Insufficient sunlight in building and night time illumination taken care by proper electrical lighting system it is called artificial lighting. In this we discussed about light and factors influencing the requirements of light.
Artificial lighting:
Artificial lighting is playing an increasingly important in modern everyday life ,and electrically produced light ,on account of its cleanliness and ease of control ,as well as low cost possesses many advantages over alternative sources wherever an electricity supply is available.
Nature of light:
For proper appreciation of modern developments in lighting studying nature of light and the fundamental principles are essential.
Light waves travel at a speed of 3*108 m/s. Another common unit is angstrom unit (AU) which is equal to 10-8cm or 10 -10 m.
Colour of light:
Different wavelengths within the above visible spectrum give light of different colours.
Before any quantitative investigations concerning lighting can be carried out it is necessary to have units in which it can be measured, the most important quantities which have be specified being luminous intensity of a source of light, the total quality of light emitted by a source, and the illumination on a given surface.
Luminous intensity:
A source of light is specified by comparing it to that of standard lamp. The unit of Luminous intensity is candle power or candela.
An ordinary 60 watt lamp has used for domestic lighting will, when viewed from the floor ,have a luminous intensity of about 70 candle power, while a searchlight viewed from along the beam may have a luminous intensity of as much as a million candle –power.
Brightness:
When the source of light covers an appreciable area, as when it is contained in an opal glass bowl or when the observer sees only reflected light as in cinema screen, the term “brightness” is employed, this being defend as the luminous intensity per unit area and expressed in candle per cm 2.
Quantity of Light -Lumens:
The total Quantity of light or luminous flux from a source is expressed in lumens, the lumen being defined by stating that the amount of light emitted from a source having a luminous intensity of one candle power in all directions is 4 lumens. An ordinary 60-watt input of about lamp will have an output of about 700 lumens
Illumination:
The illumination on a surface is governed by the amount of light or luminous flux falling on that surface and it is therefore measured conveniently in lumens per square meter.Another name for lumens per square meter lux (lx)=lm/m2. Lumen per square meter
Luminous efficiency and sensitivity of the human eye:
As human being are concerned, the existence of light becomes apparent only as a result of the radiant energy of wave lengths of between 4000 and 7500 AU, falling upon the eye, which in turn transmits sensation to the brain.
Design of lighting system:
Design of light system classified in to,
· Direct Lighting
· Indirect Lighting
· Semi-direct Lighting
· Semi –indirect Lighting
Direct Lighting
It is one of the most commonly used lighting system. In this more than 90% of total light flux is made to fall on the working plane with the help of deep reflectors. It causes shadows and glare used for industrial and general outdoor lightly.
Semi Direct Lighting:
In this scheme 60 to 90% of the total light flux is made to fall downwards directly using semi-direct reflectors while remaining light flux is used to illuminate ceiling and walls. In this Scheme is suitable for rooms with high ceilings.
Semi indirect lighting:
In this scheme 60 to 90% of the total light flux is thrown upwards to the ceiling and the rest reaches the working plane. This scheme is with soft shadows and glare free. It is used for indoor light decoration purpose.
Indirect lighting:
In this scheme more than 90% of the totals light flux thrown upwards to the ceiling by using inverted or bowed reflectors. Here glare is min. It is used for decoration purpose in cinemas theaters and hotels.
Requirement of good lighting:
A good lighting is one, under the influence of which the eyes of persons, using the light do not any strain e.g. If the light is too dim serve the objects properly or cannot do reading or writing work .On the other hand if the light is too bright our eyes start watering and are made so open forcibly. The good lighting should be comfortable while working under it.
Perfect lighting system:
The perfect lighting system should have to,
1. Provide sufficient illumination
2. Provide uniform light distribution all over the working plane
3. Provide light of suitable color
4. Avoid glare and shadow
The following factors are to be considered while designing the lighting scheme,
Illumination level:
Different types of work need a range of brightness which gives maximum output in term of quantity and quality. The degrees of illumination to give necessary brightness of the object depends on
1. The size of the object to be seen.
2. The distance between the object and the observer.
3. Contrast between the object and back ground
4. Time duration to which the objects were seen
5. Moving objects require more illumination
The illumination level required in various parts of the building are shown in the following table
Uniformity of illumination:
The human eye adjusts itself automatically to the brightness with in the field of vision. If there is a lack of uniformity, the human eye has to adjust more frequently and thus fatigue is caused to human eye and productivity is reduced. local lighting plus general lighting is adopted especially in mass production factories, offices, drawing offices, shops etc.
Colour of light:
The appearance of the body colour entirely depends upon the colour of the incident light. The composition of the light should be such that the object appears naturally. Day light LED tubes nowadays make it possible to illumination economically even large spaces with artificial day light giving good colour rendering.
Glare and shadows:
Formation of shadows causes fatigue of eyes. Shadow can be avoided by
1. Using large no of small luminaries.
2. By using wide surface sources of light.
3. By using indirect lighting system.
Direct glare from the source of light is more often a hindrance to vision. Glare can be avoided by mounting the light sources at a height above the ordinary range of vision.
Types of lamps:
1. Arc lamps
2. High temperature lamps – incandescent lamps
3. Gaseous discharge lamps
4. Fluorescent type lamp
5. CFL lamps
6. LED lamps
Arc lamps:
Electric charge discharge thro air gives intense light. The arc is struck when an electric current is made to flow through two electrodes 2 to 3 mm apart. The arc maintains the current and is very efficient source of light.
Different types of arc lamps are,
· Carbon arc lamps
· Flame arc lamps
· Magnetic arc lamps
Incandescent lamps:
When an electric current is passed through a fine metallic wire, heat is produced and the temperature of the wire increase. At low temperature the wire radiates heat energy, as the temperature of the wire increases it radiates heat as well as light energy. The higher the temperature of the wire, higher is the amount of light energy radiated
The incandescent or filament type lamp consists of a glass globe completely evacuated and a fine wire known as filament. The glass globe is evacuated to prevent the oxidation and also to prevent the temperature being lowered by radiation. The material used for filaments most posses the properties of high Melting point , low vapor pressure, high resistivity, low temperature coefficient and sufficient mechanical strength to withstand vibrations during use. Carbon, osmium and tungsten can be used as filament materials.
The types of Incandescent lamps are:
· Gas filled lamps
· Halogen lamps
Advantages of Incandescent lamps:
1. Direct operation on standard distribution of voltages.
2. Operating power factor unity.
3. Availability in various shapes and shades.
4. Good radiation characteristics in the luminous range.
5. Not affect the surrounding air temperature.
Applications of incandescent lamps:
It is used common lighting system in home, hotels and closed environments. Halogen lamps used in outdoor illumination of buildings, playing field, large gardens, car parking’s, and airport run-ways etc.
Gaseous discharge lamps:
Gases are normally poor conductors at atmospheric and higher pressure. With the application of suitable voltage called as ignition voltage across the two electrodes, there will be a discharge through the gas accompanied by electromagnetic radiation. The wave length of this radiation depends upon the gas, its pressure and the metal vapor in lamp. Argon gas, sodium and mercury vapors are commonly used in gaseous discharge lamps.
When the ionization has started in the gas, it has a tendency to increase continuously resulting in fall of circuit resistance. This is called as negative resistance characteristics. Choke or ballast is used to limit the current to a safe value. to improve power factor instead of choke condenser is used.
Advantage of Gaseous discharge lamps:
1. Used in outdoor applications.
2. Lumens efficiencies 35 to 65 lumens /watt.
3. Long bulb life -24,000 hours.
4. Lamps are typically not used in retail stores, schools, hospitals and other similar commercial applications.
Limitations:
1. Because of use of mercury disposal of lamps are not easy.
2. Lamps are typically not used in retail stores, schools, hospitals and other similar commercial applications.
Fluorescent type lamp:
A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output. Because they contain mercury, many fluorescent lamps are classified as hazardous waste.
As with the other types of lamps of discharge lamps, a choke is used in series with it a capacitor is connected. At starting, a switch short circuits the lamp and allows current to flow through the two electrodes and the choke in series; after about few seconds the switch automatically opens causing a voltage surge large enough to strike the arc between the electrodes, the arc being then maintained by the normal lamp voltages bombardment of the electrode surfaces by the positive mercury ions maintains their temperature so that they continue to emit electrons. Because of mercury filled inside a glow discharge take place.
Advantages of fluorescent lamps:
1. Energy efficient –best use of interior lighting
2. Manufacturing cost is low
3. Long life of tubes
4. Good selection of desired color temperature (cool whites to warm whites)
Limitations of florescent lamp:
1. The flickering can be present
2. Power factor is very low.
3. Poorly/cheaply designed ballasts can create fires when they overheat
.CFL lamps:
Fluorescent light and CFL lamps are very similar, but it is a compact version of fluorescent lamp that is easier to install. The glass tube is bent and both ends are fixed onto a base that holds the ballast and can fix in to ordinary incandescent bulb socket.A compact fluorescent light is an energy –saving light .The compact fluorescent tube was replaced by incandescent light .The service life also higher then incandescent light.
Advantages of CFL lamps:
1. CFLs are up to four times more efficient than incandescent bulbs.
2. CFLs use a third of the electricity and last up to 10 times as long as incandescent bulbs.
3. Just one bulb can reduce a half-ton of CO2 from the atmosphere over the life of the bulb.
Limitations of CFL lamps:
1. While CFLs are supposed to last about 10,000 hours, turning them on and off too frequently can reduce that lifetime substantially.
2. They are also sensitive to temperature, and low temperatures can cause lower light levels.
3. The most alarming thing for environmentally conscious consumers is the presence of mercury in CFLs. Mercury is a toxic metal, and while it doesn’t pose any danger when the bulb is being used, it can be released if the bulb is broken or disposed of incorrectly.
LED Lamp:
An LED is abbreviated as Light Emitting Diode. It is basically a small light producing semiconductor device capable of emitting visible light when it is that comes under “active” semiconductor electronic components. LED lamps have a life span and electrical efficiency which is several times greater than incandescent lamps. The initial cost of LED is usually higher. Degradation of LED dye and packaging materials reduces light output to some extent over time.
Like incandescent lamps and unlike most fluorescent lamps, LEDs come to full brightness without need for a warm-up time; the life of fluorescent lighting is also reduced by frequent switching on and off. Most LEDs do not emit light in all directions.
A good LED driver can guarantee a long life for an LED system and provide additional features such as dimming and control. The LED drivers can be put inside lamp or luminary, which is called a built-in type, or be put outside, which is called an independent type.
Advantages of LED lights:
1. Energy efficient- compared with other CFL, fluorescent lights for same lumens 50% less power is consumed by LED lights.
2. Long life-Quality LEDs have an expected lifespan of 30,000–50,000 hours or even longer.
3. Operated in cold storage places.
4. Durability-LEDs are breakage resistant and largely immune to vibrations and other impacts.
5. LEDs emit virtually no Infra-red radiation or Ultra violet radiation.
Energy efficient lamps:
Over the years of development in lamp technology has led to improvements in efficiency of lamps .High efficiency LED lamps can be used in place of incandescent bulbs.
Energy used by lamps:
Watt (W): is a unit of measurement used to express energy capacity of lamps.
One watt =1 Amperes *1 Volts.
Comparison of various lamps:
To compare different light bulbs, you need to know about lumens. Lumens, not watts, tell you how bright a light bulb is, no matter the type of bulb. The more lumens, the brighter the light. The above table shows more efficient lams is LED lamps.
Some Good practices in lighting:
- Use of energy efficient fluorescent in place of conventional fluorescent lamps.
- Use of compact fluorescent lamps (CFL) in place of incandescent lamps.
- Use of metal halide lamps in –lace of mercury /sodium vapor lamps.
- Use of high pressure sodium vapor (HPSV) for applications where colour rendering is not critical
- Use day lights in place of filament lamps.
- Optimum use of day lighting.
- Use of high frequency (HF) electronic ballasts in place of conventional ballasts(choke)
Conclusion:
The end of the secession the nature of light was elaborated. Many artificial lighting sources and its working were elaborately discussed. To increase the lighting quality and placement was important in building lighting system.