1. Objectives
Learn about lighting design

2. 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]

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

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

5. 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

6. 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 (Table 16-6) or from manufacturer

7. 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

8. 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.

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

10. 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)

11. 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%

12. 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 and 1.039) Correction 1.046
CU = 51.5*1.046= 54%=0.54

13. 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

14. 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=?

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

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

17. LLD
Data for fluorescent lamps

18. LDD
Ref: Tao and Janis (2001)

19. 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)

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

21. Reading Assignment
Tao and Janis
Chapter 16