Major lamp typesMajor lamp types

LAMP CHARACTERISTICSLAMP CHARACTERISTICS

1. 1. Light production mechanismsLight production mechanisms

2. Principle lamp characteristics2. Principle lamp characteristics

3. Characteristics of three main lamp types3. Characteristics of three main lamp types

(I) Tungsten filament / tungsten halogen lamps(I) Tungsten filament / tungsten halogen lamps

(II) Fluorescent / compact fluorescent lamps(II) Fluorescent / compact fluorescent lamps

(III) High intensity discharge lamps(III) High intensity discharge lamps

4. Comparison of major lamp characteristics4. Comparison of major lamp characteristics

5. Lamp applications 5. Lamp applications

1. 1. Light Production MechanismsLight Production Mechanisms

1.1 1.1 IncandescenceIncandescence 1.2 Gas discharge1.2 Gas discharge 1.3Fluorescence1.3Fluorescence

1.1 1.1 IncandescenceIncandescence

This is to pass an electric current into a metal This is to pass an electric current into a metal filament (tungsten) to heat the filament to a very high filament (tungsten) to heat the filament to a very high temperature (~3000K). It emits both heat and light.temperature (~3000K). It emits both heat and light.

For a black body radiator, proportion of visible For a black body radiator, proportion of visible radiation is maximum at about 6500K(43%).radiation is maximum at about 6500K(43%).

Temperature above or below this value will have Temperature above or below this value will have reduced proportion of visible radiation.reduced proportion of visible radiation.

1.2 1.2 Gas dischargeGas discharge

High energy electrons impinging on metal vapour can cause excitation or ionization of metal atoms. Metal ions accelerating in an alternating electric field will collide with each other to cause further excitations. When the excited ions return to their original (ground) state, they emit radiations.

Characteristics emission lines for typical metal vapours (low pressure); Mercury 254nm UV 405nm Violet 436nm Blue 546nm Green Sodium 589nm 589.6nm Orange-

Yellow

1.3 1.3 FluorescenceFluorescence

Electron in some phosphorous materials may absorb a high energy photon and goes up to a high energy level. It returns to its ground state in cascades, thus releasing its energy in small packages. The effect is to convert the absorbed (UV) radiation into visible light.

Fluorescence is useful in Mercury discharge.

2. Principle lamp characteristics

efficacy colour rendering colour temperature life available power rating fitment size run up time restriking time lumen maintenance flickering and stroboscopic effects

3. Characteristics of four main lamp types

Tungsten filament lampTungsten filament lampTungsten halogen lampTungsten halogen lampFluorescent lampFluorescent lampHigh intensity discharge lampHigh intensity discharge lamp

3.1a Tungsten filament lamp

melting temperature of tungsten — 3650Koperating temperature — 2800Klife — 1000hoursefficacy — 15 lumen/Wcolour rendering — group 1Acolour temperature — 2900K

3.1a Tungsten filament lamp

power rating — up to 1000Winstant start — no run up time requiredsmall fitment size — easy control of lightdimmablerequires no control gearhigh heat productionhigh glare if not properly shielded

3.1b Characteristics of tungsten halogen lamp

operating temperature — 3000K life — 2000hoursefficacy — 25 lumen/Wcolour rendering — better than tungsten

filament lampvery compact size — precise beam control is

possiblegood lumen maintenance

3.2 Characteristics of fluorescent lamp

life — 5000hoursefficacy — 40-100 lumen/Wcolour rendering — group 1A, 1B, 2colour temperature — 2700K – 6500Kpower rating — 8 - 125W

3.2 Characteristics of fluorescent lamp

run up time — negligiblelarge size — precise light control not possibleDimmable for modern T8 and T5 lampsrequires control gearlow heat productionnew small-bore version(compact fluorescent

lamp) can replace GLS lamp

3.3 Characteristics of high intensity discharge lamps

When fully operational, the vapour pressure may be very high (10’s atmospheres)

It takes a long time for the metal to evaporate from solid/liquid to vapour—long run up time

When it is switched off and back on again under full operation, it takes minutes to re-ignite

3.3 Characteristics of high intensity discharge lamps

The discharge phenomenon is much more complicated

Metal compounds(metal halide) can be added to produce extra emission lines to improve colour rendering

Requires special starting device(auxiliary electrode, thyristor ignitor, etc.)

3.3 Characteristics of high intensity discharge lamps

Not dimmable Efficacy generally high(50-200lm/W) Colour rendering usually poor (group 2,3,4) High lumen output, suitable for large area flood light or

high bay lighting Long life and good lumen maintenance

4.Comparison of Major Lamp Characteristics

4.1 Lamp efficacies4.2 Economic life of lamps4.3 Available power rating4.4 Run up and striking time4.5 Correlated colour temperature (CCT) and

colour rendering index (Ra)

4.1 Lamp efficacies

Lamp Efficacy(lm/W) GLS lamp 5-20 Halogen lamp 18-25 Fluorescent lamp 40-100 High pressure mercury lamp 40-60 Metal halide lamp 70-90 High pressure sodium lamp 80-120 Low pressure sodium lamp 100-200

4.2 Economic life of lamps Lamp Life(hours)GLS lamp 1000Halogen lamp 2000Fluorescent lamp 5000High pressure mercury lamp 12000Metal halide lamp 6000High pressure sodium lamp 12000Low pressure sodium lamp 10000

4.3 Available power rating

Lamp Power(W) GLS lamp and halogen lamp 15-1000 Fluorescent lamp 8-125 High pressure mercury lamp 50-1000 Metal halide lamp 250-2000 High pressure sodium lamp 70-1000 Low pressure sodium lamp 35-135

4.4 Run up and restriking time

Lamp run up time(min) restriking time(min) GLS lamp and halogen lamp nil nil Fluorescent lamp negligible negligible High pressure mercury lamp 5-7 2-7 Metal halide lamp 2-12 2-7 High pressure sodium lamp 5-7 1 Low pressure sodium lamp 5-11 <1

4.5 Correlated colour temperature (CCT) and colour rendering index (Ra)

Lamp CCT(K) Ra GLS lamp and halogen lamp 2800-3100 100 Fluorescent lamp 2700-6500 50-92 High pressure mercury lamp 3800-4400 35-50 Metal halide lamp 5000 80 High pressure sodium lamp 1900-2100 20-25 Low pressure sodium lampundefined undefined

Electromagnetic radiation and LightElectromagnetic radiation and Light

Fig. 1 Electromagnetic spectrum Fig. 1 Electromagnetic spectrum

The radiant energy from a black The radiant energy from a black body at various temperaturesbody at various temperatures

- - tungsten filament lamptungsten filament lamp

Approximate surfaceApproximate surface

temperature of suntemperature of sun

Fig.3 The radiant energy from a black body at various temperaturesFig.3 The radiant energy from a black body at various temperatures

Power distribution of lamps (approximate)Power distribution of lamps (approximate)