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1) This classroom has _______.

- Too much lighting
- Not enough lighting
- 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 room used exclusively by high school students
- A circular room with mirrors for walls
- A room used exclusively by government employees (i.e. speed/accuracy of task not important)
- 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

S/MH

- Fixture height to have even illumination

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

- Determines the fraction of light fixtures in a room that are actually used.
- Measures the fraction of emitted light that reaches a working surface.
- Is lower in a room with light-colored walls than in one with dark walls.
- 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)
- Data collection
- Room geometry
- Surface reflectances
- Fixture tables
- Preliminary calculations
- CR for room, floor, and ceiling

Calculations (continued)

- Table 16.8
- ρcc and ρfc (assume ρfc = 20% if no other information given)
- Table 16.9
- CU Multiplier if ρfc ≠ 20%
- Fixture table
- CU based on ρcc , Rw,RCR
- 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)

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?

- Type of activity performed, age of occupants, speed needed to perform activities in the building
- Shape of the rooms, distance from light fixtures to work surfaces, reflectance of surfaces, types of light fixtures in the building
- 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?

- Type of activity performed, age of occupants, speed needed to perform activities in the building
- Shape of the rooms, distance from light fixtures to work surfaces, reflectance of surfaces, types of light fixtures in the building
- 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

Summary

- Calculate number of fixtures need for a specific space
- Calculate CU
- Tuesday
- Accent lighting
- Daylighting
- Lighting quality
- Thursday
- Review

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