Rethinking the Computer Enhanced Design Process

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Electromagnetic spectrum

• Electromagnetism refers to the radiation of tiny
  oscillating electric and magnetic fields,
  commonly called photons.

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Electromagnetic spectrum

• The speed at which these oscillations occur
  depends on the temperature of the source.
• Speed is related to the wavelength and frequency
• Velocity Wavelength Frequency
• Very cold wavelength 100km
• Very hot wavelength 0.000000000001 mm

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Electromagnetic spectrum

• There are two types of energy
• Photometric energy light that is visible to the
  human eye
• Radiometric energy invisible to the human eye
  (e.g. infrared, ultraviolet)

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Electromagnetic spectrum

• Photometric energy visible light
• all of the wavelengths that constitute the
  colours of the rainbow, from red at the bottom to
  violet at the top.
• ROY G. BIV - (Red, Orange, Yellow, Green, Blue,
  Indigo and Violet).
• Speed through air 299 702 547 m/s
• Speed through glass 199 861 638 m/s
• (Causes the lens in a telescope or magnifying
  glass to work.)

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Electromagnetic spectrum
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Electromagnetic spectrum
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Measuring light

• When measuring light, there are three important
  units
• The candle
• the amount of photometric light being produced by
  the source
• The lumen
• the density of photometric light travelling
  through a particular area of space
• The lux
• the density of photometric light travelling
  through one square meter

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Measuring light

• Luminous Intensity Measures photometric light
  production
• A measure of the amount of light output by a
  source
• Units candles (CD)
• Luminous Flux Measures photometric light
  transmission
• The amount of light travelling in some direction.
  
• Units lumens (lm)
• Illuminance Measures photometric light
  incidence
• The amount of light falling on 1 m2 of a
  particular surface.
• Units lux (lx)
• Luminance Measures photometric light reflection
• A measure of the brightness of a particular
  surface
• Units candles per meter squared (CD/m²)

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Measuring light

• Example
• Luminous intensity 1 CD
• Luminous flux 2 lm
• Illuminance 1 lux
• Luminance ? (depends on material)

1 m
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Measuring light

• Example
• Luminous intensity ?
• Luminous flux ? lm
• Illuminance ? lux
• Luminance ? (depends on material)

2 m
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Measuring light

• Example
• Luminous intensity 1 CD
• Luminous flux 0.5 lm
• Illuminance 0.25 lux
• Luminance ? (depends on material)

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Natural lighting concepts
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The human eye

• The eye is not an objective instrument
• The eye does not respond equally to different
  colours
• The eye does not respond equally to different
  light levels

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The human eye

• The retina of the human eye has two categories of
  light receptor
• Rods, which are active in dim light and have no
  colour sensitivity.
• Cones, which are active in bright light and
  provide us with our ability to discriminate
  colour.
• There are three types of cones
• Beta cones
• Gamma cones
• Rho cones

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The human eye

• Perception of colour
• The eye/brain discriminates colour by processing
  the relative stimuli in the three sensors

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The human eye

• Perception of brightness
• The perceived brightness is not the same as the
  actual amount of light reflected of a surface
• In order for something to look twice as bright,
  the amount of light must be increased by a factor
  of about 4 or 5

Perceived brightness
Luminance(reflectance)
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The human eye

• There are two types of energy
• Photometric energy light that is visible to the
  human eye
• Radiometric energy invisible to the human eye
  (e.g. infrared, ultraviolet)
• However, the human eye is subjective! How many
  lumens are their in a watt, taking into account
• Changes on colour
• Changes in brightness

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The human eye

• Two types of vision have been defined
• Photopic vision
• Under bright light condition
• Rods and cones
• Scotopic vision
• Under dark light conditions
• Rods only
• For architecture, only photopic vision is
  relevant.

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The human eye

• Visual acuity is defined as a measure of the
  ability of the eye to distinguish subtle detail.
  Four factors are important
• Size the size of the object
• Luminance the amount of light being reflected
  by the object
• Contrast the difference in luminance between
  two surfaces
• Time the time required to interpret details
• The lighting designer must work with luminance
  and contrast.

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The human eye

• Minimum illuminance levels
• Car park 50 lux
• Hotel bedroom 50 lux
• Stairs and escalators 100 lux
• Foyers 100 lux
• Shopping centre 200 lux
• Lecture theatres 200 lux
• General offices 400 lux
• Laboratories 400 lux
• Food sales counters 600 lux
• Supermarkets 600 lux
• Electronics workbench 900 lux
• Jewellery workbench 1200 lux

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Daylight Factor

• We want to calculate the daylight inside a space
• How much of the light enters the space?
• How is the light distributed within the space?
• One solution
• We can calculate the illuminance on different
  surfaces in a space in LUX.

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Daylight Factor

• Illuminance depends upon two things
• The built environment predictable
• The weather not predictable !!!

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Daylight Factor

• A better solution
• Invent a new way of measuring daylight that is
  not dependent on the weather
• How?
• Use a ratio that compares the amount of light
  inside to the amount of light outside.

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Daylight Factor

• The daylight factor is defined as
• The ratio of the illuminance at a particular
  point within an enclosure to the simultaneous
  unobstructed outdoor illuminance under the same
  sky conditions
• DF Indoor illuminance / Outdoor illuminance
• DF Indoor illuminance / Design Sky
• Usually expressed as a percentage ()

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Daylight Factor

• Why use a ratio?
• Even though the sky may vary, the daylight factor
  will remain the same.
• Daylight factor is a property of the built
  environment, not the weather
• Objective measure
• Comparison between different options is possible

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Daylight Factor

• The built environment
• External elements such as site obstructions and
  applied shading devices
• The reflectivity of external surfaces
• Internal elements such as windows, skylights,
  lightshelves
• The reflectivity of internal surfaces

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Daylight Factor

• How do you calculate the daylight factor?
• There are many different methods
• Average Daylight Factor single value
  approximation for the whole space
• Projecting points projection of points over the
  sky dome and counting the visible points.
• Using protractors overlaying protractors onto
  the plans and sections of your building.
• ECOTECT simulation build a 3D model of the
  building and its apertures and let the software
  calculate the daylight factors.
• RADIANCE simulation build a 3D model of the
  building, the aperatures and the materials and
  let the software calculate the daylight factors.

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Daylight Factor

• The protractor method and ECOTECT both use the
  Split Flux method. Natural light reaches a point
  inside the building in 3 ways
• Sky Component (SC) directly from the sky
• Externally Reflected Component (ERC) from
  exterior reflections
• Internally Reflected Component (IRC) from
  interior reflections
• DF SC ERC IRC

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Daylight Factor
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Daylight Factor

• Using the protractor method
• The sky component is calculated using
  protractors.
• The externally reflected component does assumes
  all materials to have a reflectance of 0.2
• The internally reflected component is calculated
  using a simplified equation that takes into
  account some material reflectance.
• This technique is suitable for preliminary
  design.

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Daylight Factor

• ECOTECT calculates the three components by
  spraying rays for multiple points in the space.
• The sky component takes into account the light
  angle and glazing materials.
• The externally reflected component takes into
  account material reflectances and light angles.
• The internally reflected component takes into
  account some material reflectance.
• This technique is suitable for most types of
  conceptual design analysis.

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Daylight Factor

• ECOTECT example

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Daylight Factor
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Daylight Factor

• ECOTECT limitations
• Simple formula for the effect of internal
  reflections
• Does not consider multiple reflections
• Underestimate the indirect daylight reflection of
  light off multiple surfaces

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Natural light

• Daylight
• Daylight levels can also be quite variable
• Daylight is also dependent on cloud cover
• However,
• The brightness of the sky under different
  conditions can be calculated
• The designer can assume the worst case scenario

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The sky

• From the solar radiation that arrives from the
  sun
• About 25 is absorbed and scattered by air
  molecules
• About 25 is reflected back out to space
  (affected by clouds)
• About 50 arrives at the surface
• Some of this is reflected back again (affected by
  ground cover, e.g. snow)
• Due to
• Scattering by air molecules
• Scattering by suspended particulates
• Reflection by moisture vapour and clouds.
• the entire sky dome also emits light.

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The sky

• Sky types

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The sky

• As the sun and clouds move, light conditions
  change continuously.
• Cannot design for any specific situation
• Must design for average conditions

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The sky

• Standard sky models (CIE) describe average
  conditions
• The Standard Clear sky model
• The Standard Uniform sky model
• The Standard Overcast sky model
• Each model assume the level of luminance
• varies with angle from the horizon to the zenith.
• varies with the relative angle from the current
  Sun position.

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The sky

• Standard sky models

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The sky

• The Standard Overcast sky model
• Completely clouded sky
• The Sun is not visible
• Produces white light
• If the atmosphere is heavily polluted the
  overcast sky colour appearance can be slightly
  yellow

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The sky

• The Standard Clear sky model
• No clouds
• The Sun is visible
• Blue sky
• Nitrogen dioxide makes the colour of the
  atmosphere slightly brown

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The sky

• Sky models give only the distribution of
  luminance over the sky dome, not the total amount
  of light coming from it, also known as the Sky
  Illuminance.
• Illuminance The amount of light falling on 1 m2
  of a particular surface (lux)
• Sky illuminance depends on latitude
• At the equator, sky illuminance is high
• Away from the equator, sky illuminance decreases

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The sky

• Sky illuminance changes continuously. Therefore,
  some kind of average is required. This is called
  the Design Sky Value
• The value used for design
• The value represents the worst case
• Design Sky Value means
• The value that is exceeded 85 of the time
• Derived by statistical analysis

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The Sky

• Design Sky Values

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Behaviour of light

• Light exhibits 5 important behaviours
• Inverse square law
• Cosine law
• Reflection
• Transmission
• Refraction
• Diffraction

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Inverse square law
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Cosine law
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Reflection
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Transmission
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Refraction
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Diffraction
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Behaviour of light

• Useful interactive diagrams at
• http//www.squ1.com

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