L16: Daylighting Flashcards
What is daylighting?
The use of light from the sun and sky to complement or replace electric light
What are the goals of high-performance daylighted commercial buildings?
- Meet design objectives and adopt holistic design
- Maximise occupant comfort and productivity
- Maximise building value
What is the visible spectrum?
Wavelength range of electromagnetic radiation visible to human eye
What do treatments to glazing aim to do?
Stop infrared without stopping visible light
What is visual transmittance?
A measure (0-1) of the amount of visible light that passes through the glazing material of a window
Why is the VT for single pane clear, double pane clear, double pane reflective and double pane low-e clear?
Single pane clear - 0.89
Double pane clear - 0.8
Double pane high reflective - 0.1
Double pane low-e clear - 0.7
What are the types of glare?
Disability glare
Discomfort glare
What is the efficacy of clear sky?
150 lumens/watt
What does direct sunlight provide?
Illuminance too intense for task lighting
What does direct sky light provide?
Less illuminance than direct sunlight but still intense; daylighting design focuses on diffusing light
What are indirect natural light sources?
Matte reflective surfaces or translucent glazing to diffuse direct light eg. light scoop, tubular skylight, switchable privacy glass
What is the daylight factor?
Ratio of interior to exterior illuminance (gives illuminance as a % of what it would be without building and just under overcast sky)
How are designs tested?
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
What ist he 15/30 rule?
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
What can be used when straight plans are undesirable?
Finger plans - but can obstruct sky if too tall
Where is light most abundant and uniform?
North facade
What is the second most important exposure after north facade?
South - light less abundant but uniform diffuse
Why is east and west exposure minimised?
Glare, unwanted solar heat transfer
What is a courtyard?
Most compact variation of finger plan; creates more obstruction to sky and blocks East/West sun
What are atriums?
Similar to courtyards except glazing at roof replaces wall glazing but still obstructs sky and heat gain in summer
What are light wells?
Atriums below clearstories or roof monitors; less light but reduced heat gain
What are translucent partitions used for?
Allows side light to be borrowed by deeper spaces
How does the height of the window effect the daylighting zone?
Higher window = deeper daylighting zone
height x 1.5
How does adding a light shelf affect the daylight zone depth?
Height x 2.0
How does adding a highly reflective light shelf affect the daylight zone depth?
Height x 2.5
What do strip windows do?
Provide more uniform daylight than punched windows
What glass should be used for view and daylight?
View - tinted, lower VT to control glare
Daylight - higher VT to allow in max light
What are the suggested interior surface reflectance values for ceilings, walls, floors and furniture?
Ceilings - over 80%
Walls - 50-70%
Floors 20-40%
Furniture - 25-45%
What are light shelves?
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
What is the main advantage of light shelves?
Reduces glare near window
Does added reflectance from light shelves onto ceiling make up for obstructing the sky?
No
How should light shelves be tilted?
North facade at 40º
East/west at 15º
What should ambient illumination levels be?
Significantly less than task levels but not below 1/3
What is direct lighting?
Light comes straight down from fixture
What is indirect lighting?
Light is reflected off the ceiling
Which type of lighting best matches daylight distribution?
Direct/indirect lighting
What can be done to the back wall to balance light in a deep room?
Wallwash - use ceiling fixtures 2 ft from wall with cool colour temp to balance illumination difference and avoid gloomy feeling
What are photosensors?
Controls light fixtures depending on light levels measured in the room; usually coupled with motion sensors
What is critical for achieving targeted energy savings when using sensors and controls?
Commissioning
How does the cost of dimming controls compare to switching controls?
Double
How do occupants react to dimming/switching controls?
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
How should switching systems be controlled to avoid occupant dissatisfaction?
Light level for switching off should be double that for switching on
What is the dimming response time and what should it be set to?
Time it takes the system to respond to sudden change in light levels
Approx 30s to avoid unnecessary response to temporary changes
What happens if the photosensor field of view is too narrow?
Sample of measured light will be too sensitive to small incidental changes
How does combining photosensors and occupant sensors work?
If photosensor determines daylight levels are sufficient, occupant sensor is deactivated but manual switch also provided to override system
What is a common way controls are made to turn lights on/off?
Turned on manually and turned off automatically
How should spaces be zoned for lighting?
Parallel to daylight source; should reflect space use
What is multi level switching?
Individual lamps can be switched on/off within a larger fixture containing more lamps
What is split-wiring?
Stepped switching - light levels change in discrete steps so less abrupt
Can sensor and control systems be factory set and why?
No because modelled environment differs from real, physical space
When is calibration done?
Once furnishings are in place and redone if interiors are changed
