Major lamp types

LAMP CHARACTERISTICS 1. Light production mechanisms 2. Principle lamp characteristics 3. Characteristics of three main lamp types (I) Tungsten filament / tungsten halogen lamps (II) Fluorescent / compact fluorescent lamps (III) High intensity discharge lamps 4. Comparison of major lamp characteristics 5. Lamp applications

1. Light Production Mechanisms 1.1 Incandescence 1.1 Incandescence 1.2 Gas discharge 1.2 Gas discharge 1.3Fluorescence 1.3Fluorescence

1.1 Incandescence r This is to pass an electric current into a metal filament (tungsten) to heat the filament to a very high temperature (~3000K). It emits both heat and light. p For a black body radiator, proportion of visible radiation is maximum at about 6500K(43%). p Temperature above or below this value will have reduced proportion of visible radiation.

1.2 Gas discharge q q 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. q q Characteristics emission lines for typical metal vapours (low pressure); Mercury254nmUV 405nmViolet 436nmBlue 546nmGreen Sodium589nm 589.6nm Orange-Yellow

1.3 Fluorescence p p 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. p p Fluorescence is useful in Mercury discharge.

2. Principle lamp characteristics p p efficacy p p colour rendering p p colour temperature p p life p p available power rating p p fitment size p p run up time p p restriking time p p lumen maintenance p p flickering and stroboscopic effects

3. Characteristics of four main lamp types q Tungsten filament lamp q Tungsten halogen lamp q Fluorescent lamp q High intensity discharge lamp

3.1a Tungsten filament lamp q q melting temperature of tungsten — 3650K q q operating temperature — 2800K q q life — 1000hours q q efficacy — 15 lumen/W q q colour rendering — group 1A q q colour temperature — 2900K

3.1a Tungsten filament lamp q q power rating — up to 1000W q q instant start — no run up time required q q small fitment size — easy control of light q q dimmable q q requires no control gear q q high heat production q q high glare if not properly shielded

3.1b Characteristics of tungsten halogen lamp p p operating temperature — 3000K p p life — 2000hours p p efficacy — 25 lumen/W p p colour rendering — better than tungsten filament lamp p p very compact size — precise beam control is possible p p good lumen maintenance

3.2Characteristics of fluorescent lamp q q life — 5000hours q q efficacy — lumen/W q q colour rendering — group 1A, 1B, 2 q q colour temperature — 2700K – 6500K q q power rating — W

3.2Characteristics of fluorescent lamp q q run up time — negligible q q large size — precise light control not possible q q Dimmable for modern T8 and T5 lamps q q requires control gear q q low heat production q q new small-bore version(compact fluorescent lamp) can replace GLS lamp

3.3Characteristics of high intensity discharge lamps q q When fully operational, the vapour pressure may be very high (10’s atmospheres) q q It takes a long time for the metal to evaporate from solid/liquid to vapour—long run up time q q When it is switched off and back on again under full operation, it takes minutes to re-ignite

3.3Characteristics of high intensity discharge lamps q q The discharge phenomenon is much more complicated q q Metal compounds(metal halide) can be added to produce extra emission lines to improve colour rendering q q Requires special starting device(auxiliary electrode, thyristor ignitor, etc.)

3.3Characteristics of high intensity discharge lamps q q Not dimmable q q Efficacy generally high(50-200lm/W) q q Colour rendering usually poor (group 2,3,4) q q High lumen output, suitable for large area flood light or high bay lighting q q Long life and good lumen maintenance

4.Comparison of Major Lamp Characteristics r r 4.1 Lamp efficacies r r 4.2 Economic life of lamps r r 4.3 Available power rating r r 4.4 Run up and striking time r r 4.5 Correlated colour temperature (CCT) and colour rendering index (Ra)

4.1 Lamp efficacies LampEfficacy(lm/W) q q GLS lamp 5-20 q q Halogen lamp18-25 q q Fluorescent lamp q q High pressure mercury lamp40-60 q q Metal halide lamp70-90 q q High pressure sodium lamp q q Low pressure sodium lamp

4.2 Economic life of lamps LampLife(hours) q q GLS lamp1000 q q Halogen lamp 2000 q q Fluorescent lamp5000 q q High pressure mercury lamp12000 q q Metal halide lamp 6000 q q High pressure sodium lamp q q Low pressure sodium lamp 10000

4.3 Available power rating LampPower(W) q q GLS lamp and halogen lamp q q Fluorescent lamp8-125 q q High pressure mercury lamp q q Metal halide lamp q q High pressure sodium lamp q q Low pressure sodium lamp35-135

4.4 Run up and restriking time Lamp run up time(min) restriking time(min) q q GLS lamp and halogen lamp nil nil q q Fluorescent lampnegligiblenegligible q q High pressure mercury lamp q q Metal halide lamp q q High pressure sodium lamp5-71 q q Low pressure sodium lamp5-11<1

4.5 Correlated colour temperature (CCT) and colour rendering index (R a ) Lamp CCT(K) Ra q q GLS lamp and halogen lamp q q Fluorescent lamp q q High pressure mercury lamp q q Metal halide lamp q q High pressure sodium lamp q q Low pressure sodium lampundefined undefined

Electromagnetic radiation and Light Fig. 1 Electromagnetic spectrum

The radiant energy from a black body at various temperatures - tungsten filament lamp - tungsten filament lamp Approximate surface Approximate surface temperature of sun temperature of sun Fig.3 The radiant energy from a black body at various temperatures

Power distribution of lamps (approximate)