1) This classroom has _______.

A) Too much lighting

B) Not enough lighting

C) About the right amount of lighting

2) For which of the following conditions would you increase the weighting factor by

+1 in a lighting design?

A) A room used exclusively by high school students

B) A circular room with mirrors for walls

C) A room used exclusively by government employees (i.e. speed/accuracy of task not important)

D) A room used for cutting dark stone

Objective

• Use room geometry to calculate coefficient of utilization (CU)

Now what?

• We now know how much light we need.

• How do we get it?• Zonal cavity method

• Calculate CU

• How much light makes it from the fixture to the work surface of interest

• Graphical methods (similar to stress strain)• Ray tracing

• Computationally intensive

Illumination Calculation

• Iws = N × LPL × LOF × CU / A

• N = number of fixtures

• LPL = rated lumens per fixture

• LOF = lamp operating factor• Ballast, voltage, temperature, position (HID)

• CU = coefficient of utilization• Fraction of light that meets the work surface

• A = room area

Lamps are Not the only thing

• Fixtures (luminaires)• Lamp type and number• Power requirements• Ballast• Application requirements• Mounting• Fixture control• Special features• Distribution

Ref: Tao and Janis (2001)

S/MH

• Fixture height to have even illumination

3) In lighting design, the coefficient of utilization __________.

A) Determines the fraction of light fixtures in a room that are actually used.

B) Measures the fraction of emitted light that reaches a working surface.

C) Is lower in a room with light-colored walls than in one with dark walls.

D) Depends on the type of task performed, accuracy required by the task, and on the ages of occupants in a room.

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• 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 reflectances (ρcc, ρw, ρfc)• Tables in Tao and Janis (pg 92-93, 102-107) or

from manufacturer

Calculation Procedure

• Goal is to get CU (how much light from the fixture gets to the work surface)

1. Data collection• Room geometry• Surface reflectances• Fixture tables

2. Preliminary calculations• CR for room, floor, and ceiling

Calculations (continued)

3. Table 16.8• ρcc and ρfc (assume ρfc = 20% if no other

information given)

4. Table 16.9• CU Multiplier if ρfc ≠ 20%

5. Fixture table• CU based on ρcc , Rw, RCR

6. Use CU by multiplier from step 4.

Example

• Classroom (30 × 30 × 9)

• White ceiling, blackboards on 2 sides, light floor

• Students working on desks

• Fluorescent fixtures at ceiling level

• Use standard tables

Data So Far

• 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

• ρcc = Rc = 70% (b/c CCR = 0)

• ρrc = Rw = 30%

• ρfc = 20% (assumption)

Variations

• Fixture 2 (pg 92), 1 ft from ceiling

• Actual fixture, original height

• Original fixture, 30% reflective floor

Fixture 2

• PAR = 2 × (L+ W)/(L × W) = 120ft/900ft2

• CCR = 2.5 × PAR × hc = 0.33

• RCR = 2.5 × PAR × hr = 1.83

• FCR = 2.5 × PAR × hf = 0.83

• ρcc = 64% (Table 16-8)

• ρrc = Rw = 30%

• ρfc = 20% (assumption, could use Table 16-8)

Ref: Tao and Janis (2001)

Actual Fixture

• 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

• ρcc = Rc = 70% (b/c CCR = 0)

• ρrc = Rw = 30%

• ρfc = 20% (assumption)

More Reflective Floor

• 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• ρcc = Rc = 70% (b/c CCR = 0)• ρrc = Rw = 30%• ρfc = 30% (given, could use Table 16-8 Tao

and Janis)

4) If a building owner hires Persephone to determine the amount of lighting in an existing

building, Persephone would need to know which parameters?

A) Type of activity performed, age of occupants, speed needed to perform activities in the building

B) Shape of the rooms, distance from light fixtures to work surfaces, reflectance of surfaces, types of light fixtures in the building

C) Color rendering index, evenness of lighting, thermal properties of lighting in the building

5) If a developer hires Francisco to determine the required lighting levels for a new building,

Francisco would need to know which parameters?

A) Type of activity performed, age of occupants, speed needed to perform activities in the building

B) Shape of the rooms, distance from light fixtures to work surfaces, reflectance of surfaces, types of light fixtures in the building

C) Color rendering index, evenness of lighting, thermal properties of lighting in the building

Illumination Calculation

• Iws = N × LPL × LOF × CU / A

• N = number of fixtures

• LPL = rated lamp lumens per fixture

• LOF = lamp operating factor• Ballast, voltage, temperature, position (HID)

• CU = coefficient of utilization• Fraction of light that meets the work surface

• N = Iws × A / (LPL × LOF × CU)

Distribution

• Direct 90 – 100 % downward

• Semi-direct 60-90% down, rest upward

• Direct-indirect/general diffuse

• Semi-indirect

• Indirect

Ref: Tao and Janis (2001)

Ref: Tao and Janis (2001)

Summary

• Calculate number of fixtures need for a specific space• Calculate CU

• Tuesday• Accent lighting

• Daylighting

• Lighting quality

• Thursday• Review