P.1 Book E3 Section 1.2 Lighting Lighting and environmental protection Types of lighting Check-point 2 Check-point 3 Check-point 4 Measuring brightness Check-point 5 Choosing lamps Check-point 6 1.2Lighting

P.2 Book E3 Section 1.2 Lighting Lighting and environmental protection Energy-saving lamps use 75% less energy than traditional filament lamps. Are there any setbacks in using energy-saving lamps? They contain poisonous substances which can cause severe pollution. Is energy-saving the only concern for environmental protection?

P.3 Book E3 Section 1.2 Lighting 1 Types of lighting Main sources of artificial lighting in Hong Kong include: Incandescent lamps Gas discharge lamps Light emitting diodes They produce light by electron transition. (e – move from one energy level to another)

P.4 Book E3 Section 1.2 Lighting 1 Types of lighting An electron can only reside at one of the allowed energy levels. With enough energy, an electron can move to a higher energy level. Atom becomes unstable.  Electron will return to a lower energy level.

P.5 Book E3 Section 1.2 Lighting 1 Types of lighting An electron moves from a higher energy level to a lower one. More energy released  higher frequency  The excess energy can be released as EM wave.

P.6 Book E3 Section 1.2 Lighting 1 Types of lighting a Incandescent lamps (filament lamps) i Conventional incandescent lamps Incandescent lamp The first electric light invented Has a thin wire (filament) made of tungsten or tungsten based alloy inside a glass globe

P.7 Book E3 Section 1.2 Lighting i Conventional incandescent lamps Voltage across the filament  Energy of the electrons in heated filament   Electrons excited to different energy levels ( ∵ Energy levels of solid metals are closely-spaced)  Excited electrons jump back to lower energy levels  EM waves of a board range of f emitted

P.8 Book E3 Section 1.2 Lighting i Conventional incandescent lamps ~90–95% of the emission is not visible light  Cannot be utilized for illumination purposes Most of them is infra-red radiation (heat)  Waste energy However,

P.9 Book E3 Section 1.2 Lighting i Conventional incandescent lamps When the lamp is turned on, the high-temperature filament evaporates and oxidizes.  Inert gas is filled to slow down the evaporation. Thinner part of the filament is hotter.  Evaporates faster  Even thinner until it breaks  The lamp fails.

P.10 Book E3 Section 1.2 Lighting a Incandescent lamps (filament lamps) ii Halogen lamps Halogen lamp is an incandescent lamp that contains a halogen gas (e.g. bromine or iodine)  Helps maintain the filament thickness and lengthens the lifetime  Slightly more efficient than an incandescent filament lamp Halogen lamps usually fail the same way as ordinary incandescent lamps do.

P.11 Book E3 Section 1.2 Lighting ii Halogen lamps Halogen lamps can work at higher temperature.  More efficient in emitting visible light However, UV radiation is also produced.  Should have UV filtering properties

P.12 Book E3 Section 1.2 Lighting Check-point 2 – Q1 In an atom, when an electron absorbs enough energy, it moves from a ( lower / higher ) energy level to a ( lower / higher ) energy level. When the electron returns to a ( lower / higher ) energy level, it emits __________________. energy / EM waves

P.13 Book E3 Section 1.2 Lighting Check-point 2 – Q2 Halogen lamps contain a __________ gas which slows down the rate of evaporation of _________ at ( low / high ) temperature. This allows the halogen lamps to work at a ( lower / higher ) temperature than conventional incandescent lamps. halogen filament

P.14 Book E3 Section 1.2 Lighting 1 Types of lighting b Gas discharge lamps Gas discharge lamps include: Fluorescent tube lamps Compact fluorescent lamps High-intensity discharge lamps

P.15 Book E3 Section 1.2 Lighting b Gas discharge lamps i Fluorescent tube lamps (FTL) Sealed glass tube: contains an inert gas (e.g. argon) under very low pressure and a small amount of mercury. Inner wall coated with phosphor powder Electrode at each end: A high voltage is applied across them when the lamp is turned on. 1.1 Fluorescent tube lamps Simulation mercury Structure of FTL

P.16 Book E3 Section 1.2 Lighting i Fluorescent tube lamps (FTL) The 3 stages of generation of light:  e – are emitted and ionize the gas inside.  The e – and ions move to the +ve and –ve electrodes respectively (discharge).  The current causes the mercury to vaporize. 1.High voltage is applied across the electrodes.

P.17 Book E3 Section 1.2 Lighting i Fluorescent tube lamps (FTL)  Excess energy is released in the form of EM waves (mainly UV radiation). 2.The mercury atoms are excited by the collision with the electrons and ions.

P.18 Book E3 Section 1.2 Lighting i Fluorescent tube lamps (FTL)  A broad range of visible light is emitted for illumination purposes. This process is called fluorescence. 3.Phosphor coating on the inside of the tube absorbs the UV radiation.

P.19 Book E3 Section 1.2 Lighting i Fluorescent tube lamps (FTL) In a lighting circuit, a fluorescent tube is connected with a starter and a ballast. Starter: to start up the lamp Ballast:  To maintain a stable discharge inside the fluorescent tube  To keep a stable light output

P.20 Book E3 Section 1.2 Lighting b Gas discharge lamps ii Compact fluorescent lamps (CFL) Compact fluorescent lamp (CFL) Also called energy-saving lamp Very similar to FTL Twisted tube and rearranged positions of pins  Able to be fitted into traditional incandescent lamp sockets With self-contained ballast which is more efficient than that in an FTL

P.21 Book E3 Section 1.2 Lighting b Gas discharge lamps iii High-intensity discharge lamps (HID) High-intensity discharge lamp (HID) For long time, high output uses Works at high pressure and temperature Needs several kV to start up and several minutes to warm up to full brightness Does not need a phosphor coating.  Produce visible light directly by electron transitions.

P.22 Book E3 Section 1.2 Lighting Check-point 3 How does an FTL produce light? Arrange the following steps in the correct order. ___  ___  ___  ___  ___  ___ ABCD E F AThe mercury vaporizes. BElectron transition occurs in the mercury atoms to emit EM waves (mainly UV radiation). CThe phosphor coating emits visible light. DA high voltage is applied across the tube. EThe inert gas is ionized. FThe phosphor coating absorbs UV radiation.

P.23 Book E3 Section 1.2 Lighting 1 Types of lighting c Light emitting diodes (LED) Light emitting diodes (LED) has n-type and p-type semiconductors sandwiched together n-type (negative) has excess e –  Same behavior as free e – p-type (positive) has a shortage of e –  As if there are +ve charge carriers (holes)

P.24 Book E3 Section 1.2 Lighting c Light emitting diodes (LED) LED connected a battery  An electric field set up across the junction  Charge carriers with different electrical PE in the two different layers LEDs use d.c. voltage ∵ Can only work in one direction 1.2 P-n junction in an LED Simulation

P.25 Book E3 Section 1.2 Lighting c Light emitting diodes (LED) When an e – moves across the junction and combines with a hole, it moves to a lower energy level.  EM wave emitted. The range of frequency of emitted light is narrower than that of an incandescent lamp.  LED is more efficient. Suitable f  Emitted wave is visible light.

P.26 Book E3 Section 1.2 Lighting c Light emitting diodes (LED) Advantages of LED: White LEDs and almost any colour LED can be produced now  have many uses Low production cost High efficiency Long lifetime (> hrs)

P.27 Book E3 Section 1.2 Lighting An n-type semiconductor has (excess / a shortage of) electrons. A p-type semiconductor has (excess / a shortage of) electrons. Check-point 4 – Q1

P.28 Book E3 Section 1.2 Lighting Check-point 4 – Q2a Does current flow in this circuit?No

P.29 Book E3 Section 1.2 Lighting Check-point 4 – Q2b Does current flow in this circuit?Yes

P.30 Book E3 Section 1.2 Lighting Check-point 4 – Q2c Does current flow in this circuit?No

P.31 Book E3 Section 1.2 Lighting Check-point 4 – Q2d Does current flow in this circuit?No

P.32 Book E3 Section 1.2 Lighting a Luminous flux Human eye  Detect light with between 380–760 nm  Other lights should be emitted at higher power to give the same brightness. Most sensitive to green-yellow light ( ~ 555 nm) 2 Measuring brightness

P.33 Book E3 Section 1.2 Lighting a Luminous flux High-energy light source  bright  Need to consider human vision Luminous flux is the power output of a light source, corrected for the dependence on wavelength of the sensitivity of the human eye. Unit: lumen (lm), symbol: F Represents only the power of visible light Practically more useful than the power rating

P.34 Book E3 Section 1.2 Lighting 2 Measuring brightness b Illuminance Unit: lux (lx) 1 lx = 1 lm m –2 Measuring brightness with a light meter Expt 1a Illuminance = luminous flux area E = FAFA i.e. The illuminance E at a surface is the luminous flux per unit area falling on the surface.

P.35 Book E3 Section 1.2 Lighting Experiment 1a Measuring brightness with a light meter 1.Set up the apparatus. The receptor of the light meter should face the lamp normally. 2.Switch on the lamp and the light meter. The light meter should receive light from the lamp only.

P.36 Book E3 Section 1.2 Lighting Experiment 1a Measuring brightness with a light meter 1.1 Expt 1a - Measuring brightness with a light meter 3.Take the reading (E ) of the light meter and separation (r ) between light meter and centre of lamp. 4.Estimate the luminance flux F by F = 4  r 2 E. Video

P.37 Book E3 Section 1.2 Lighting b Illuminance If a light source has equal flux in all directions,  Illuminance  as distance  Size of each surface  r 2  E  ……(1) 1 r 2  Inverse square law

P.38 Book E3 Section 1.2 Lighting b Illuminance Consider the light with luminous flux F falling on a surface A. If the light hits the surface at angle  to the normal, flux  surface = F ’ = F cos .  E ’ = F ’ A = F cos  A = E cos   E  cos  ……… (2) (Lambert’s cosine law) Combining (1) & (2), = F cos  4  r 2 E

P.39 Book E3 Section 1.2 Lighting b Illuminance Finding illuminance Example 3 The illuminance in some daily cases:

P.40 Book E3 Section 1.2 Lighting Finding illuminance Example 3 An HID lamp of 6400 lm is placed at X (2 m above a table). What is the illuminance at A and B respectively? Regard the lamp as a point source. At A, r = 2 m and  = 0 . Illuminance = F cos  4  r 2 = 127 lx = 6400  cos 0  4  (2) 2

P.41 Book E3 Section 1.2 Lighting Example 3 Finding illuminance At B, r 2 = (BX ) 2 = (AX ) 2 + (AB ) 2 = = 5 m 2 cos  = AX BX Illuminance = F cos  4  r 2 = 91.1 lx = 2525 = 4  54   2525

P.42 Book E3 Section 1.2 Lighting 1.The luminous flux at a book directly below a lamp can be increased by moving it ( closer to / further from ) the lamp. 2.The illuminance at a book will be at the ( maximum / minimum ) when light is 90  to the normal of the book. Check-point 5 – Q1–2

P.43 Book E3 Section 1.2 Lighting Check-point 5 – Q3 A CFL with a luminous flux of 2100 lm is placed at P. Illuminance at X = ? = F cos  4  r 2 Illuminance at X = 2100  cos 30  4   = 44.7 lx

P.44 Book E3 Section 1.2 Lighting 3 Choosing lamps a Energy efficiency Efficacy measures how much energy is converted into visible light (effectiveness of a light source), corrected for the dependence on wavelength of the human eye. Efficacy = luminous flux input electrical power Unit: lm W –1 Efficacy of a CFL Example 4

P.45 Book E3 Section 1.2 Lighting Example 4 Efficacy of a CFL A CFL has a luminous flux of 900 lm and a power rating of 15 W. What is its efficacy? Efficacy = = 60 lm W –1

P.46 Book E3 Section 1.2 Lighting a Energy efficiency Blue light and green light Example 5

P.47 Book E3 Section 1.2 Lighting Example 5 Blue light and green light There are two 880-lm monochromatic lamps A and B. Lamp A : 40 W, emits 555-nm green light Lamp B : 80 W, emits 510-nm blue light (a)Explain whether the lamps appear to have the same brightness. They appear to have the same brightness because they have the same luminous flux.

P.48 Book E3 Section 1.2 Lighting Example 5 Blue light and green light (b) What is the efficacy of each lamp? Efficacy of lamp A = = 22 lm W –1 = 11 lm W –1 Efficacy of lamp B = There are two 880-lm monochromatic lamps A and B. Lamp A : 40 W, emits 555-nm green light Lamp B : 80 W, emits 510-nm blue light

P.49 Book E3 Section 1.2 Lighting 3 Choosing lamps b Comparing different types of electrical lighting We need to consider the cost effectiveness while choosing light. Factors included: price lifetime efficacy

P.50 Book E3 Section 1.2 Lighting b Comparing different types of electrical lighting Comparison of some typical lamps: Comparing the efficiency of different types of light sources Expt 1b

P.51 Book E3 Section 1.2 Lighting Experiment 1b Comparing the efficiency of different types of light sources 1.Set up the apparatus. 2.Switch on the lamp and the light meter. The light meter should receive light from the lamp only. 3.Read the illuminance.

P.52 Book E3 Section 1.2 Lighting Experiment 1b Comparing the efficiency of different types of light sources 1.2 Expt 1b - Comparing the efficiency of different types of light sources Video 5.Repeat the experiment with a CFL. Wait for 5 mins for the CFL to reach its full brightness before taking readings. 4.Determine the input energy by timing how long it takes for a certain amount of electrical energy supplied via the kilowatt-hour meter.

P.53 Book E3 Section 1.2 Lighting bComparing different types of electrical lighting Home lighting Example 6

P.54 Book E3 Section 1.2 Lighting Example 6 Home lighting Incandescent lamp : 60 W, $15 CFL : 11 W, $40 Cost of electricity = $0.9 per kW h The light is used 4 hours a day. (a)How long will it take for the difference in the cost of electricity to compensate the difference in the price? same luminous flux

P.55 Book E3 Section 1.2 Lighting Example 6 Home lighting (a)Cost of electricity of CFL each day = 0.9  (11  10 –3 )  4 = $ Cost of electricity of incandescent lamp each day = 0.9  (60  10 –3 )  4 = $0.216 Difference in cost of electricity each day = – = $ Time needed = 40 – = 142 days

P.56 Book E3 Section 1.2 Lighting Example 6 Home lighting (b) Compare the cost effectiveness of the two lamps. Although the price of the CFL is higher than that of the incandescent lamp, it consumes less electrical energy and the cost of using it is less. In the long run, the CFL is more cost effective.

P.57 Book E3 Section 1.2 Lighting Check-point 6 – Q1 An energy saving lamp has a luminous flux of 2700 lm and a power rating of 45 W. Find its efficacy. Efficacy = luminous flux input electrical power = 60 lm W – =

P.58 Book E3 Section 1.2 Lighting Check-point 6 – Q2 Which of the following kinds of lamp is the least cost effective? A Incandescent lamp B Gas discharge lamp C White light emitting diode

P.59 Book E3 Section 1.2 Lighting The End