Department of Technical Education Andhra Pradesh Name : P. Balanarsimlu Designation : Lecturer Branch : Electrical Engineering Institute : Govt. Polytechnic Nizamabad Year/Semester : VI Semester Subject : Electrical Utilisation and Traction Subject Code : EE605A Topic : Electric Lighting Duration : 50 Mins Sub Topic : Units of wave length & Definitions of light parameters Teaching Aids : PPT, Diagrams,Animation Revised By : K.Chandra Sekhar, L/EEE, GPT, HYD 9EE605A.2

Recap In the last class you have learnt about Nature of Light and its Propagation 9EE605A.2

Objectives On completion of this topic You would be able to know The Units of Wave Length Definitions of the terms used in Lighting 9EE605A.2

Wave Length Since wave lengths of light are very small , “Angstrom unit” is chosen (AU or AO) as the unit of wave length Angstrom unit (AU or AO) =10-7 mm =10-8 cm =10-10m 9EE605A.2

Wave Length Micron is also used to represent wave length 1 Micron ( μ ) = 10-6m Wave length ( λ ) = Velocity of light propagation (v) Frequency (f) Fig.1 9EE605A.2

Definitions Plane Angle () A plane angle is the angle subtended at a point in a plane by two straight converging lines OR When two straight lines lying in the same plane meet at a point, the angle between these converging lines at that point is know as “plane angle” Arc Radius  Arc Radius O Fig.2 radians  = 180 π degrees One radian = 9EE605A.2

Definitions 2) Solid angle (ω) A solid angle is the angle subtended at a point in the space by an area and is the angle enclosed In the volume formed by an infinite number of lines lying on the surface of the volume and meeting at the point Solid angle(ω) = area/(radius)2 = A/r2 steradian area S ω Radius Fig.3 9EE605A.2

Lumen = candle power X solid angle Definitions 3)Flux or luminous flux (Φ or F) It may be defined as “ the rate of energy radiated in the form of light waves by a luminous body” Radiant energy time Φ or F= lumens Lumen = candle power X solid angle = c.p. X ω 9EE605A.2

Definitions 4)Luminous intensity ( I ) or Candle power (C.P.) It is the luminous flux per unit solid angle in a given direction Luminous flux I or C.P.= Lumen/steradian or candela Solid angle F I or C.P.= Lumen/steradian or candela ω 9EE605A.2

Definitions 5) Illumination ( E ) = Illumination of a surface is defined as the luminous flux received by the surface per unit area It is represented by the symbol E and is measured in “lux” (or meter candle or lumen/m2). Illumination E = Flux F or Φ = Area A 9EE605A.2

Definitions 6)Brightness (B or L) It is defined as the luminous intensity of the lamp per unit projected area of either light source or the reflecting surface B or L = I/A cd/m2 I=luminous intensity (candela) A= Projected or normal area (m2) 9EE605A.2

Definitions 7)Mean horizontal candle power (M.H.C.P.) Is the average candle power in the horizontal plane passing through the luminous center of the lamp 8)Mean spherical candle power (M.S.C.P) Is the average candle powers in all directions and in all planes emitting from the source of light Total flux 4π M.S.C.P.= 9EE605A.2

Definitions 9) Mean horizontal spherical candle power (M.H.S.C.P.) It is the mean of candle powers in all directions above or below the horizontal plane passing through the source of light. (usually lower part) Total flux emitted in hemisphere 2π M.H.S.C.P.= 9EE605A.2

Definitions 10)Lamp efficiency It is the ratio of the output i.e luminous flux in lumens to the electrical power input in watts Lamp efficiency = Luminous flux Lumen/watt Electric power 9EE605A.2

Definitions 11.Polar Curves The luminous intensity or candle power is not uniform in all directions, due to its unsymmetrical shape and design It is essential to know exactly how the light is distributed and is usually given in the form of polar curves Polar curve is defined as a graph representing the light distribution of a lamp (luminous intensity) in a horizontal or vertical plane 9EE605A.2

Lamp and horizontal plane Polar Curves Lamp and horizontal plane On horizontal plane On vertical plane Fig.4b Fig.4c Fig.4a 9EE605A.2

Horizontal Polar Curves Fig 4a shows an incandescent lamp. If the luminous intensity is measured in a horizontal plane about a vertical axis, a curve is plotted between luminous intensity and the angular position as shown in Fig 4b Fig.4a Fig.4b 9EE605A.2

Horizontal Polar Curves Fig.4b The drop in luminous intensity along OC at 00 of horizontal polar curve is due to break in the filament where the current enters and leaves 9EE605A.2

Vertical Polar Curves On vertical plane Fig.4c On vertical plane If the luminous intensity is measured in a vertical plane at various angles, a polar curve in a vertical plane is obtained The drop or depression in luminous intensity at 1800 of vertical polar curve is due to the position of the lamp holder 9EE605A.2

Summary Units of Wave Length So far we have discussed about Definitions of Plane angle Solid angle Luminous flux Luminous intensity Illumination Brightness 9EE605A.2

Definitions of M.H.C.P M.S.C.P M.H.S.C.P Lamp efficiency Polar Curves Contd… Definitions of M.H.C.P M.S.C.P M.H.S.C.P Lamp efficiency Polar Curves 9EE605A.2

Quiz 1Q. Lux is the unit of A) Illumination B) Flux C) Luminous intensity D) Solid angle 9EE605A.2

Quiz 2Q. The unit of lamp efficiency is A) C.P./Watt B) Watts/ Lumen C) Lumens/Watt D) Lumens / Steradian 9EE605A.2

Quiz 3Q. One radian is equal to_______ degrees. A) 180/2π B) 360/π C) π/180 9EE605A.2

Quiz 4Q. The largest solid angle subtended is ____steradian. A) π C) π/4 D) 1/π 9EE605A.2

Frequently Asked Questions Define a) Plane angle and b) Solid angle Define Luminous flux and intensity Define Illumination and Luminous efficiency Define M.H.C.P., M.S.C.P. and M.H.S.C.P Draw and explain the vertical and horizontal polar curves 9EE605A.2

THANK YOU 9EE605A.2