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Objectives Finish Lighting system design Daylighting
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Illumination Calculation
E = N × F × LLF × LOF × CU / A E = selected illuminance [fc, lx] N = number of fixtures F = installed lumens per fixture [lm] LLF = Light loss factor depreciation, position (dust deposit) LOF = lamp operating factor Ballast, voltage CU = coefficient of utilization Fraction of light that meets the work surface A = room area [ft2, m2] N = E A / (F × LLF × LOF × CU )
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Zonal Cavity Method Figure 16-1 Ref: Tao and Janis (2001)
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Calculate Cavity Ratios
CR = 2.5 × PAR × h PAR = perimeter to area ratio = P/A PAR = 2 × (L+ W)/(L × W) h = height of cavity What about CR for non-rectangular rooms? CR = 5 × (L+ W)/(L × W) × h
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Reflectance Experience Convert to effective reflectance (ρcc, ρw, ρfc)
White ceiling, Rc = 70 – 80 % = ρc White walls, Rw = % = ρw Medium to light colored walls, Rw = 50 % =ρw Dark wood paneling, Rw = 25 % = ρw Floor, Rf = % = ρf Convert to effective reflectance (ρcc, ρw, ρfc) Tables in Tao and Janis (pg , Table 16-6) or from manufacturer
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Calculation Procedure
Goal is to get CU (how much light from the fixture gets to the work surface) Data collection Room geometry Surface reflectance Fixture tables Preliminary calculations CR for room, floor, and ceiling
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Calculations (continued)
Table 16.6 ρcc and ρfc (assume ρfc = 20% if no other information given) Table 16.7 CU Correction if ρfc ≠ 20% Fixture table (Figure 16-6 page 523, or manufacturer) CU based on ρcc , ρ w, RCR Use CU by multiplier from step 4.
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Example Classroom (30 × 30 × 9)
White ceiling, Medium colored walls, Light floor Students working on desks Fluorescent fixtures at ceiling level Use standard tables
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Solution PAR = 2 × (L+ W)/(L × W) = 120ft/900ft2
CCR = 2.5 × PAR × hc = 0 (ceiling cavity ration) RCR = 2.5 × PAR × hr = 2.17 (room CR) FCR = 2.5 × PAR × hf = 0.83 (floor CR) Ceiling reflectance 70% (white ceiling) Wall reflectance 50% (medium colored walls) Floor reflectance 30% (light color - 30 % is maximum)
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Solution (continue) Use Table 16-6
Effective ceiling cavity reflectance: CCR =0, Ceiling reflectance 70% , Wall reflectance 50% → (table) → 70 % (because CCR=0) ρCC= 70% Effective floor cavity reflectance: FCR=0.83 (use 2.2) , Floor reflectance 30%, Wall reflectance 50% → (table) → 28% ρFC= 28% Effective wall cavity reflectance (does not change) ρW= 50%
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Solution (continue) Use Figure 16-6 (page 525) Luminary 15 is the most similar to the one in classroom: RCR =2.2, ρCC= 70%, ρW= 50% → (figure) → (interpolation between 52 and 45) CU=51.5% CU Correction if ρFC ≠ 20% (table 16.7) ρFC=28 ≈ 30 and ρCC= 70%, ρW= 50%, RCR =2.2 → (table) → (interpolation between and 1.048) Correction 1.055 CU = 51.5*1.055= 54%=0.54
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Zonal Cavity Method N = E × A / (F × LLF × LOF × CU)
Instilled lamp lumens per fixture F=? Light loss factor LLF=? lamp operating factor LOF=?
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Lamp operating factor LOF
LOF= VF × BF VF – Voltage factor Table 16-4 BF - Ballast factor Table 16.5
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Lamp Loss factor LLF LLF= LLD × LDD
LLD – Lamp lumen deprecation (manufacturer or Figure When you use Figure 15-9 use values for 70% of rated lamp life.) LDD – Luminarie Dirt Depreciation Figure 16.2 (from Figure find maintenance category and then use Figure 16.2 )
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LLD Data for fluorescent lamps
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LDD Ref: Tao and Janis (2001)
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Example for LOF and LLF calculation
HID mercury lamps (250 W) in fixture type 18 (Figure 16.6), magnetic ballast, voltage oscillation 2%, cleaning period is 12 months, very dirt environment. - Voltage oscillation (drop) of 2% →Table 16.4 → VF=0.95 - Magnetic ballast →Table 16.5 → BF=0.95 (additional table) LOF=VF*BF=0.95*0.95= From Figure 16.6 maintenance category is V. Very dirt environment and cleaning period 12 months→ Figure → LDD=0.7 Mercury lamps (250 W) → table → LLD= 80%. LLF=LDD*LLD= 0.7*0.8=0.54
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Rated lamp lumens per fixture F
F = Number of lamps per fixture × Lumens per lamp Number of lamps per fixture – from Figure 16- 6 Lumens per lamp –manufacturer or table in your book
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Example for calculation of F
HID mercury lamp (250 W) in fixture type 18 (Figure 16.6), magnetic ballast, voltage oscillation 2%, cleaning period is 12 months, very dirt environment. Fixture type 18 → Figure 16.6 → Only one lamp per fixture Mercury lamp (250 W) → Table 15.4 (initial lumen) → lum F=1*12500=12500 lumens
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Finally calculate the number of luminarie - N
N = E × A / (F × LLF × LOF × CU)
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Handouts Step-by-step procedure Best source is IESNA Handbook
General guidance in your textbook Best source is IESNA Handbook IESNA - Illuminating Engineering Society of North America Focuses much more on quality issues
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Distribution of luminarie S/MH
Goal is to have even illumination
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Table to calculate S for S/MH ration
Ref: Tao and Janis (2001)
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Summary Calculate CU Calculate number of fixtures need for a specific space Do not ignore S/MH ration when you distribute lamps
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What is the difference between this two pictures
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Daylighting computer simulation
Radiosity method
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What about lighting quality?
Zonal cavity calculations focus on light quantity Quality can not be ignored CRI, evenness of illumination, transition between light and dark, flicker, glare, color temperature Quality is very important
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Daylighting Scientific and psychological studies have found:
People prefer buildings where changes in sunlight exterior affect interior lighting Properly lit spaces are preferred to underlit or overlit spaces Diffuse lighting is preferred to direct lighting North sky lighting is ~universally preferred
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What are problems with daylighting?
Can require extensive controls Requires extra hardware to avoid direct lighting Can require expensive glazing Can damage works of art Need to limit the amount of heat associated with solar gains
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Strategies for Daylighting
Orient your building on an East-West axis Limit direct sunlight with exterior shades, light shelves, clerestory windows, translucent glazing Control glazing and conventional lighting with controls Occupancy sensors Automatic blinds Light-level sensors
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Reading Assignment Tao and Janis
Chapter 16 and section 17.1, 17.2, and 17.4
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