Artificial light calculation

Transcription

1 56 1- Point-by-point method Exercise: Find E at point a & b due to: 1- only one lamp above point a. 2- The 3 lamps shown in the figure 3- E at 85 for both points 1- Ea= lx Eb= 85.7 lx 2- Ea= lx Eb= lx 3- E= 0 57 For calculate the required lamps number for a space to ensure the recommended level of illuminance (E) according to the space s function. E = n.φ.m f.u f A Where, E: illuminance in Lux n: number of lamps ϕ: flux per lamp M f : maintenance factor U f : utilization factor A: area of space Eq.1 1

2 58 Maintenance factor (Mf) based on multi factors. The most three important are: a) Lamp Lumen Depreciation (LLD): This factor depends upon the type of lamp and the replacement schedule. Use the following when exact data are unavailable. 59 Maintenance factor (Mf) based on multi factors. The most three important are: b) Luminaire Dirt Depreciation (LDD): This factor depends upon luminaire design, atmosphere conditions in the space, and maintenance schedule. Conditions Value Functions V.Clean 0.95 Operation rooms Clean 0.85 Houses, lecture rooms, offices Dirty 0.75 Kitchens, light industrial factories V.Dirty 0.5 Heavy & dirt industrial factories 2

3 60 Maintenance factor (Mf) based on multi factors. The most three important are: C) Room Surface Dirt Depreciation (RSDD): This factor is self-explanatory. Conditions Value V.Clean 0.95 Clean 0.85 Dirty 0.75 V.Dirty For calculate the required lamps number for a space to ensure the recommended level of illuminance (E) according to the space s function. F = E.A.δ η.u f Eq.2 Where, E: illuminance in Lux F: total flux in the space δ : dust deposit U f : utilization factor η: lumen output ratio A: area of space Dust deposit (δ) Value small Average 1.4 High

4 62 Lighting calculation steps: 1- Considerations of space function: (E, GI, etc.) 2- Determine the space specifications: Room index (K), surface reflection, U f 3- Selection of lighting system components (from catalogue): type of lamps, LOR, weight, dimension, type of installation, protector; class, etc. 4- Calculations: I- Suspension index (J ), 0 J 1 II- Room index (K) k = a.b h m (a + b) h' J = h'+h m h h m h h wp III-Find Utilization factor: (from U f table according to J, K and class of luminaire), 63 Photometric Class of Luminaires 4

5 64 Luminaires example : Catalogues snapshot 65 IIII-Layout: distribution of luminaires to ensure uniform lighting), a = Y (n L y ) n y, e y = a + L y b = x (n L x ) n x, e x = b + L x X e x b e x /2 e y a VI- Uniform spacing (e Tr & e Log ) S max = h m 1.5 Uniformity (U) = E min /E max 60% Y e y /2 5

6 66 Minimum initial illumination (MIE) This value depends on two factors: 1-Factor of space= 70% 2-Factor of time= 1.25 Ex. What is MIE for required E = 40 lx MIE= 40/0.7= 57 lx In function of time, 57*1.25=71 lx. Is the illumination level upon which we have to design our space. 67 Glare index (GI) Glare is a visual impression created by the presence of illuminated area in the field of view. It can cause tiredness, errors and injuries. 6

7 68 Unified Glare Rating (UGR) or (GI) The prevention can be achieved by several means: 1- First of them is correct placement of luminaires. 2- The light source should be covered or partially obstructed 3- Use large luminaires with low luminance, 4- Surface finishes that diffuse and scatter light should be used instead of glossy ones that create strong reflections 5- luminaires with appropriate distribution of luminous density should be used 69 Unified Glare Rating (UGR) or (GI) UGR ratings. Recommended limiting glare indices. Zone Region UGR Discomfort Zone Comfort Zone Intolerable (not suited for work lighting) >28 Just intolerable 28 Uncomfortable 25 Just Uncomfortable 22 Acceptable 19 Just acceptable 16 Noticeable 13 Just Perceptible (no glare) 10 Working area Maximum allowed UGR Drawing rooms 16 Offices 19 Industrial work, fine 22 Industrial work, medium 25 Industrial work, coarse 28 7

8 70 Unified Glare Rating (UGR) Calculate GI by using UGR method The UGR method relates to glare from ceiling fixtures that are placed in a regular pattern. X = b H Y = a H b View direction: Crosswise a View direction: Endwise H = h h' Unified Glare Rating (UGR) X = b H Y = a H H = h h' 1.2 8

9 72 Unified Glare Rating (UGR) Calculate GI by using Söllner Diagram The Söllner Diagram is a graphical representation of the calculated luminance values in the area between 45 and 85 to the vertical. Measures to limit discomfort glare by downlights mainly relate to this area. The slanted lines indicate the allowed limit values. The limit values depend on the quality class of the eye task and on the rated value of the illuminance. 73 There is no glare in the space wherever the position of the luminaires There is a glare for all luminaires have gamma angle between 45 & 55 9