Why is daylighting important?
- improve energy efficiency by minimising use of electricity in artificial lighting (with condition to consider cooling and heating loads as well)
- influence health and well being, visual comfort, health and productivity
What are factors affecting daylighting in building?
- sunpath
- building site and obstructions
- daylighting available (sky condition)
What design considerations can we look at to control daylighting in buildings?
- site design
- building orientation
- building form
- envelope design
- exterior and interior shading and treatments
What are general design goals for buildings in terms of lighting?
- maximise indirect daylighting
- minimize glare
- design to suit the function
How does the sun’s angles affect daylight?
the sun angles differ which change the sun’s penetration, behaviour in buildings and building shadows (winter and summer sun)
How do designers account for daylight today?
They use complex software that analyses sunpaths etc (e.g Velux)
What is the average daylight factor formula and what are the factors?
formula that calculates the average DF or daylight factor where:
T = diffuse transmittance of glazing material (as a decimal)
W = area of glazing (m^2)
Θ = angle from the centre of the window subtended by visible sky (degrees)
CF = correction factors (dirt and frame)
A = total area of all indoor surfaces (m^2)
R = average area weighted reflectances of all indoor surfaces (decimal)
What is a good range of daylight factor?
2-5
What are some strategies/principles for designing with daylight in mind?
considering site design by studying shadowing and site obstacles - surrounding building heights, setbacks (spacing between neighbours, any other obstacles including vegetation)
How can you orientate your building to maximise glazing without conflicting with excess solar radiation?
North - best for daylighting (uniform and soft)
South - daylighting is uniform and excess solar radiation can be easily controlled
East/West - sun is very low and horizontal and it is hard to control (devices are usually used)
What is the role of both internal and external hading devices?
to protect against direct sunlight, to prevent over solar radiation
What are light shelves?
devices that can can diffuse/reflect the light and can prevent direct sunlight entering a room
What wavelength is the eye most sensitive at?
at about 555nm which is yellow or yellow/green, this is the brightest colour to the eye
What is glare?
to shine with oppressive brightness - when there is an imbalance (brightness) of an interior (where one part is much brighter than the general) then glare occurs.
As wavelength decreases does energy increase or decrease?
energy intensity of radiation increases with decreasing wavelength
What is the minimum light level for visibility?
50 lux for paper and textiles, 150 lux for paintings (gallery)
What is the light lux for a typical classroom?
500 lux
To conclude what are the 5 main aspects we should consider with lighting?
- quantity - provide ambient lighting requirements during daytime hours for the majority of the year
- quality - create uniform distribution of daylight to reduce uncomfortably high brightness ratios, control direct sunlight when necessary and utilise beneficial passive solar strategies when appropriate
- usability - allow for user adjustment and override, ensure adequate daylight to all occupants of the daylight space, provide view and connection to the outdoors
- building integration - fully integrate with the architectural expression of the building inside and out, fully integrate with other building systems - HVAC, electrical, lighting, structural, interiors
- cost effectiveness - implement within overall construction budget of the project, achieve significant energy savings by reducing lightning lighting energy costs and associated cooling energy costs
