Objectives Learn about lighting design

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]

Zonal Cavity Method Purpose is to get CU “fixture efficiency” What parameters do you need?

Figure 16-1 Ref: Tao and Janis (2001)

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

Reflectance Experience Convert to effective reflectance (ρcc, ρw, ρfc) White ceiling, Rc = 70 – 80 % = ρc White walls, Rw = 60 - 70 % = ρw Medium to light colored walls, Rw = 50 % =ρw Dark wood paneling, Rw = 25 % = ρw Floor, Rf = 10-30 % = ρf Convert to effective reflectance (ρcc, ρw, ρfc) Tables in Tao and Janis (Table 16-6) or from manufacturer

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

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, or manufacturer) CU based on ρcc , ρ w, RCR Use CU by multiplier from step 4.

Example Classroom (30 × 30 × 9) White ceiling, Medium colored walls, Light floor Students working on desks Fluorescent fixtures at ceiling level Use standard tables

Solution PAR = 2 × (L+ W)/(L × W) = 120ft/900ft2 CCR = 2.5 × PAR × hc = 0 RCR = 2.5 × PAR × hr = 2.17 FCR = 2.5 × PAR × hf = 0.83 Ceiling reflectance 70% (white ceiling) Wall reflectance 50% (medium colored walls) Floor reflectance 30% (light color - 30 % is maximum)

Solution Use Table 16-6 Effective ceiling cavity reflectance: CCR =0, Ceiling reflectance 70% , Wall reflectance 50% → (table) → 70 % (because CRC=0) ρCC= 70% Effective floor cavity reflectance: FCR=0.83, Floor reflectance 30%, Wall reflectance 50% → (table) → 29% ρFC= 28% Effective floor cavity reflectance (does not change) ρW= 50%

Solution ρFC=28 ≈ 30 and ρCC= 70%, ρW= 50%, RCR =2.2 → (table) → Use Figure 16-6 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 1.048 and 1.039) Correction 1.046 CU = 51.5*1.046= 54%=0.54

Illumination Calculation E = N × F × LLF × LOF × CU / A N = number of fixtures F = Installed lamp lumens per fixture LLF = Light loss factor Depreciation, Dirt LOF = lamp operating factor Ballast, voltage CU = coefficient of utilization Fraction of light that meets the work surface

Design E = N × F × LLF × LOF × CU / A N = E × A / (F × LLF × LOF × CU) or N = E × A / (F × LLF × LOF × CU) Instilled lamp lumens per fixture F=? Light loss factor LLF=? lamp operating factor LOF=?

Lamp operating factor LOF LOF= VF × BF VF – Voltage factor Table 16-4 BF - Ballast factor Table 16.5

Lamp Loss factor LLF LLF= LLD × LDD LLD – Lamp lumen deprecation (manufacturer or Figure 15-9. When you use Figure 15-9 use values for 40% of rated lamp life.) LDD – Luminarie Dirt Depreciation Figure 16.2 (from Figure 16- 6 find maintenance category and then use Figure 16.2 )

LLD Data for fluorescent lamps

LDD Ref: Tao and Janis (2001)

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 – from manufacturer Finally calculate N (number of luminarie)

Summary Calculate number of fixtures need for a specific space Calculate CU Calculate: F, LLF, LOF

Reading Assignment Tao and Janis Chapter 16