LIGHT SOURCE•Electric energy is converted to light energy where heat is the sideeffect.

1. Incandescent lamps: general incandescent bulbs.• Most commonly used• Least expensive• Their soft, warm glow is reminiscent

of candle light.• Least efficient lighting source –

approx. 90% of the electricity goesinto heat generation rather than lightproduction.

INCANDESCENT BULB •Bulbs convert power into light by passing electric current through a filament of tungsten wire. The wire consists of minicoils. •The current heats the tungsten filament until it glows. •The glass bulbs are filled with an inert gas mixture primarily of argon and nitrogen.•The bulb can be clear, diffuse, tinted or coloured.•It gives out attractive warm yellow light.

•Also called GLS – General Lighting Service Lamp – used for domestic purpose. •Standard incandescent lamps last about 750 – 1000 hours.

ADVANTAGES & DISADVANTAGES OF INCANDESCENT LAMPS

INCANDESCENT & HALOGEN LAMP

•Start & warm up almost instantly & can be extinguished & restarted at will.

•Ordinary incandescent lamps – 5 to 20 Lumens / Watt

•Halogen lamps – 15 to25 Lumens / Watt

Advantage Disadvantage

Low initial cost High operating cost

Creates inviting environment Fragile

Immediate starting Short life

Easily dimmed Low lumen per watt

Variety of shapes, sizes, and applications High heat output

Easy to install

HALOGEN BULB (tungsten-halogen lamp)•Slightly different shape & thicker heavier glass bulb.• An incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. •In ordinary incandescent bulb the filament evaporates over time & bulb wall blackens slowly as tungsten is deposited on it.•The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle which increases the lifetime of the filament and prevents darkening of the bulb by redepositing tungsten from the inside of the bulb back onto the filament.

•Lamp life ranges from 2000 hours to 10,000 hours.•Whiter & brighter throughout its life.

LOW VOLTAGE HALOGEN LAMPS

•Low voltage & smaller - throws bright light on a precise spot – highly focused light.

•Comes with an inbuilt transformer that reduces the voltage from 220 volt to 12 volt.

•Halogen low voltage lamps are available in a variety of voltages and strengths. Voltages extend from 6V to 50V, while the performance levels lie between 10W and 590W.

•Tungsten halogen low voltage lamps are used today in many applications. Originally developed for photography, they have now won a place in traffic and signaling systems and in general indoor and outdoor lighting system.

LOW VOLTAGE HALOGEN LAMPS

•Compact but effective.

•Provides upto 50% more light than conventional voltage halogen system using same amount of energy.

•Used for – accent or display lighting / suspended down light or track-lights generally used in retail & commercial areas / domestic areas.

Halogen: a series of non-metal elements, comprising fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At). The group of halogens is the only periodic table group which contains elements in all three familiar states of matter (e.g., solid, liquid & gas) at standard temperature and pressure.

MOST COMMON APPLICATIONS

Ordinary incandescent lamps are used in – residences, hotels & motels & some retail environment where residence like quality is desired.

Halogen lamps – residential down lights, outdoor lighting, hotels, motels, retail display in recessed lighting, track lighting & other lamp holders in stores of all kinds.

Low voltage halogen lamps – used in museums, galleries, residences, landscape lighting, special effects like cove lighting and illumination inside and under cabinets.

FLUORESCENT LAMPS• Introduction in 1938

•Aesthetically they are second class – unpopular with interior designer

•Widely used because they are more efficient than incandescent lamps.

Glass tubes coated on interiors with phosphor – a chemical compound that emits light when activated by ultraviolet energy.

Air in the tube is replaced with argon gas & a small amount of mercury is added.

When f. lamp is turned on, the electricity heats cathodes at each end causing them to emit electrons, which in turn create an electric arc between the cathodes. The electrons in this arc collide with mercury vapour & argon or other gas atoms to produce invisible ultraviolet rays. These rays excite the fluorescent phosphor coating, producing visible light.

Fluorescents are highly efficient because 80% of their light comes from the phosphor coating.

BASIC COMPONENTS OF A FLUORESCENT LAMP

• BULB: usually a straight glass tube - can be circular, U-shaped, or curved .

•PHOSPHOR: coating inside the bulb that transforms ultraviolet radiation into visible light. The colour of the light produced depends upon the composition of phosphor.

•BASE: used to connect the lamp to the circuit & support it in the fixture.

•CATHODE: located at each end of the lamp. Cathodes are coated with a material that emits electrons & usually are made of coiled coil or single coil tungsten wire.

•GAS: argon or a mixture of inert gas at low pressure – krypton sometimes is used.

•MERCURY: a minute quantity of liquid mercury is placed in the bulb to furnish mercury vapour.

BASIC COMPONENTS OF A FLUORESCENT LAMPS

COMPACT FLUORESCENT LAMP•It is a fluorescent lamp designed to replace an incandescent lamp.• Some types fit into light fixtures formerly used for incandescent lamps. •The lamps use a tube which is curved or folded to fit into the space of an incandescent bulb.

•FL & CFL – provides good energy efficiency.•FL & CFL can used in many places –homes, businesses etc.

•Smaller in size•Different shapes – folded, spiral, circular.•Available in 9 watt to 26 watt.•It saves 75% of energy•Generally used for commercial lights

LAMP LIFE & EFFICIENCY•Fluorescent lamps 4/5 times more efficient.•40 watt incandescent lamp produces 445 lumens.

40 watt fluorescent lamp produces 3050 lumens•40 watt incandescent lamp – 1500 hours

40 watt fluorescent lamp – 20,000 hours

BRIGHTNESS

23 WATT = 100 WATT

LAMPLIFE10,000 HOURS 750 HOURS

POWER CONSUMPTION25% 100%

EFFICACY COMPARISIONCompact fluorescent bulbs are more efficient than incandescent bulbs in brightness, power consumption & lamp life.

BULB REPLACEMENT COSTOne 23 watt CFL lasts as long as 18 incandescent bulbs –thereby saving the cost of replacing those bulbs.

HID LAMPS (HIGH-INTENSITY DISCHARGE )

•Designed to emit a great deal of light from a compact, long-life light source.

•Most often used for street, parking lot lighting & for large indoor spaces like gymnasiums & industrial work force.

•Energy efficient – producing 50 to 100 lumen per watt.

TYPES OF HID LAMPS:Metal Halide LampsSodium LampsMercury Vapour Lamps

METAL HALIDE LAMP

•Produce white light .•Available in many sizes – compact lamps used in track lighting & table lamps to huge lamps for lighting stadiums. •Colour of light slightly greenish –used where colour is not critical -e.g., sports arenas, parking lots, landscape lighting & building floodlights.

The color rendering index (CRI) is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in color-critical applications such as photography and cinematography.

SODIUM LAMP

•Two types:High pressure sodium lamp (HPS) Low pressure sodium lamp (LPS)

•HPS works on principle of ionizing of sodium vapours – provides more light than any other lamp – offer very high lumens/watt – yellow colour used on bridges, railway lines, tunnels, road lighting, parking lots, heavy industrial work places, ware housing, security lighting – where light colour is not so important.•LPS are even higher in lumens/watt –but colour is so poor that their use is limited to security lighting.

MERCURY VAPOUR LAMP

•Older type of lamp that remains in common use as streetlights & security lights.

•Compare to other HID lamps MVL have relatively poor colour & low energy efficiency – almost never used in new construction.

•It has a white light.

•Used on bridges, railway lines & bridges – but not in factories because it has a tendency to flicker (an inconstant or wavering light).

•Also known as flood light.