L16: Daylighting Flashcards

1
Q

What is daylighting?

A

The use of light from the sun and sky to complement or replace electric light

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2
Q

What are the goals of high-performance daylighted commercial buildings?

A
  1. Meet design objectives and adopt holistic design
  2. Maximise occupant comfort and productivity
  3. Maximise building value
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3
Q

What is the visible spectrum?

A

Wavelength range of electromagnetic radiation visible to human eye

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4
Q

What do treatments to glazing aim to do?

A

Stop infrared without stopping visible light

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5
Q

What is visual transmittance?

A

A measure (0-1) of the amount of visible light that passes through the glazing material of a window

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6
Q

Why is the VT for single pane clear, double pane clear, double pane reflective and double pane low-e clear?

A

Single pane clear - 0.89
Double pane clear - 0.8
Double pane high reflective - 0.1
Double pane low-e clear - 0.7

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7
Q

What are the types of glare?

A

Disability glare

Discomfort glare

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8
Q

What is the efficacy of clear sky?

A

150 lumens/watt

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9
Q

What does direct sunlight provide?

A

Illuminance too intense for task lighting

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10
Q

What does direct sky light provide?

A

Less illuminance than direct sunlight but still intense; daylighting design focuses on diffusing light

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11
Q

What are indirect natural light sources?

A

Matte reflective surfaces or translucent glazing to diffuse direct light eg. light scoop, tubular skylight, switchable privacy glass

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12
Q

What is the daylight factor?

A

Ratio of interior to exterior illuminance (gives illuminance as a % of what it would be without building and just under overcast sky)

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13
Q

How are designs tested?

A

Scaled, physical models with light cells which measure interior light levels to assess character, glare, adequacy and balance of light
OR software to assess daylighting and electric lighting

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14
Q

What ist he 15/30 rule?

A

Tasklighting in15ft perimeter zone is daylight; next 15ft is daylight and electric; beyond 30ft only uses electric
= Work areas must be kept within 30ft of exterior

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15
Q

What can be used when straight plans are undesirable?

A

Finger plans - but can obstruct sky if too tall

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16
Q

Where is light most abundant and uniform?

A

North facade

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17
Q

What is the second most important exposure after north facade?

A

South - light less abundant but uniform diffuse

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18
Q

Why is east and west exposure minimised?

A

Glare, unwanted solar heat transfer

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19
Q

What is a courtyard?

A

Most compact variation of finger plan; creates more obstruction to sky and blocks East/West sun

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20
Q

What are atriums?

A

Similar to courtyards except glazing at roof replaces wall glazing but still obstructs sky and heat gain in summer

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21
Q

What are light wells?

A

Atriums below clearstories or roof monitors; less light but reduced heat gain

22
Q

What are translucent partitions used for?

A

Allows side light to be borrowed by deeper spaces

23
Q

How does the height of the window effect the daylighting zone?

A

Higher window = deeper daylighting zone

height x 1.5

24
Q

How does adding a light shelf affect the daylight zone depth?

A

Height x 2.0

25
Q

How does adding a highly reflective light shelf affect the daylight zone depth?

A

Height x 2.5

26
Q

What do strip windows do?

A

Provide more uniform daylight than punched windows

27
Q

What glass should be used for view and daylight?

A

View - tinted, lower VT to control glare

Daylight - higher VT to allow in max light

28
Q

What are the suggested interior surface reflectance values for ceilings, walls, floors and furniture?

A

Ceilings - over 80%
Walls - 50-70%
Floors 20-40%
Furniture - 25-45%

29
Q

What are light shelves?

A

Horizontal shelves that reflect daylight onto ceiling and shield direct glare from sky provides more even distribution; should be above eye height and not visible within room

30
Q

What is the main advantage of light shelves?

A

Reduces glare near window

31
Q

Does added reflectance from light shelves onto ceiling make up for obstructing the sky?

A

No

32
Q

How should light shelves be tilted?

A

North facade at 40º

East/west at 15º

33
Q

What should ambient illumination levels be?

A

Significantly less than task levels but not below 1/3

34
Q

What is direct lighting?

A

Light comes straight down from fixture

35
Q

What is indirect lighting?

A

Light is reflected off the ceiling

36
Q

Which type of lighting best matches daylight distribution?

A

Direct/indirect lighting

37
Q

What can be done to the back wall to balance light in a deep room?

A

Wallwash - use ceiling fixtures 2 ft from wall with cool colour temp to balance illumination difference and avoid gloomy feeling

38
Q

What are photosensors?

A

Controls light fixtures depending on light levels measured in the room; usually coupled with motion sensors

39
Q

What is critical for achieving targeted energy savings when using sensors and controls?

A

Commissioning

40
Q

How does the cost of dimming controls compare to switching controls?

A

Double

41
Q

How do occupants react to dimming/switching controls?

A

Dimming is less disturbing; switching is disruptive and often gets manually disabled so should be used for spaces with all-day adequate light and non-critical visual tasks

42
Q

How should switching systems be controlled to avoid occupant dissatisfaction?

A

Light level for switching off should be double that for switching on

43
Q

What is the dimming response time and what should it be set to?

A

Time it takes the system to respond to sudden change in light levels
Approx 30s to avoid unnecessary response to temporary changes

44
Q

What happens if the photosensor field of view is too narrow?

A

Sample of measured light will be too sensitive to small incidental changes

45
Q

How does combining photosensors and occupant sensors work?

A

If photosensor determines daylight levels are sufficient, occupant sensor is deactivated but manual switch also provided to override system

46
Q

What is a common way controls are made to turn lights on/off?

A

Turned on manually and turned off automatically

47
Q

How should spaces be zoned for lighting?

A

Parallel to daylight source; should reflect space use

48
Q

What is multi level switching?

A

Individual lamps can be switched on/off within a larger fixture containing more lamps

49
Q

What is split-wiring?

A

Stepped switching - light levels change in discrete steps so less abrupt

50
Q

Can sensor and control systems be factory set and why?

A

No because modelled environment differs from real, physical space

51
Q

When is calibration done?

A

Once furnishings are in place and redone if interiors are changed