Introduction to Illumination.pptx

An introduction to illumination. how to calculate it using Lambert's law. Basic definitions are presented and its relation to electric application

1. Utilization of Electric Energy (EPR 513) Chapter 1: Illumination Presented by: Dr Mariam A. Sameh 1

2. Introduction to Illumination 2

3. Introduction to Illumination 3

4. Introduction to Illumination 4

5. Basic Definitions Plane angle: is the angle subtended at a point and is enclosed by two straight lines lying in the same plane. In radians, plane angle is the ratio   5

6. Basic Definitions Solid angle (ω) is the angle subtended at a point in space by an area OR it 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. 6

7. Basic Definitions 7

8. Basic Definitions In steradian, solid angle is the ratio . It can also be defined as the angle subtended at the center of the sphere by a part of its surface having an area equal to (radius) 2 . The solid angle for a point source:   8

9. Basic Definitions Luminous flux (F) is the light energy radiated out per second from the body in the form of luminous light waves [Lumens]. It is also the basic quantity of illumination. Luminous intensity (I) or Candle-power (c.p) of a point source in a given direction is the luminous flux (number of lumens) radiated out per unit solid angle [Candela]. 9

10. Basic Definitions Mean spherical candle-power (MSCP): it is given by flux (in lumen) emitted in all directions in all planes divided by 4π.   10

11. Basic Definitions Mean Horizontal candle-power (MHSCP): It is given by the total flux emitted in a hemisphere (usually the lower one) divided by the solid angle subtended at the point source by the hemisphere.   11

12. Basic Definitions Illumination (E) or Illuminance: it is the luminous flux received by a surface per unit area. [Lux or Lumens/m 2 ] When the luminous flux falls on a surface, it is said to be illuminated.   12

13. Basic Definitions 13 Some of examples of illumination value in residential and commercial rooms Note: For industrial lighting, ask for the specific requirements from the consultants/ users.

14. Basic Definitions Reduction Factor of a source of light is the ratio of its mean spherical candle power to its mean horizontal candle power.   14

15. Basic Definitions Brightness (B) of a surface is defined as the luminous intensity per unit projected area of the surface in the given direction[Lambert].   15

16. Basic Definitions Color Rendering Index (CRI) is a measure of the effect of light on the perceived color of objects. A low CRI indicates that some colors may appear unnatural when illuminated by the lamp. 16

17. Basic Definitions 17

18. Basic Definitions 18

19. Basic Definitions 19

20. Basic Definitions Specific efficiency of a lamp is the ratio of luminous flux to the power intake. Its unit is lumens per watt ( lm /w). 20

21. Laws of Illumination There are several theorems and formulas are used to study and analyze illumination. However, most of them are concentrated on two laws. 21

22. Laws of Illumination law of inverse squares: states that the illumination of a surface (E) is inversely proportional to the square of the distance of the surface from the source (r).   22

23. Laws of Illumination Lambert’s Cosine law: states that the illumination of a surface (E) is proportional to the cosine of the angle between the normal at the point and the direction of luminous flux.   23

24. Laws of Illumination From the laws of illumination, we can conclude that the illumination at any point on surface (E) due to a source has a luminous intensity (I), can be given as: so, the law of illumination:   24

25. Summary 25 Quantity Symbol Law Unit Solid angle ω Stredians Liminous Flux F --- Lumens Luminous Intensity I Candela or candle power Illumination E Lux or Lumens/m2 Specific efficiency η luminous/Watt Quantity Symbol Law Unit Solid angle ω Stredians Liminous Flux F --- Lumens Luminous Intensity I Candela or candle power Illumination E Lux or Lumens/m2 Specific efficiency η luminous/Watt

26. Examples A light source producing 1500 candela is suspended 2.2 m above a horizontal surface. Calculate the illumination produced on the surface 2.5 m away ( at Q) 26

27. Examples Two lamps are suspended 10m apart and at a height of 3.5 m above a surface. Each lamp emits 350cd. Calculate. the illuminance on the surface midway between the lamps, the illuminance on the surface immediately below each of the lamps 27

28. Examples 28

29. Examples 29 Solution: (a)

30. Examples 30

31. Try it yourself 31 A lamp of 100 c.p is suspended 3 m above the horizontal plane. Calculate the illumination at a point on the horizontal plane: Directly below the lamp. 3 m away from the vertical axis.

32. Try it yourself 32 Solution: E = 11.11 lux E= 7.85 lux

33. Questions??! 33