Building PhysicsIntroduction to architectural science

Lecture 3Prepared by:

Dr. Yahia Elbashar

1Dr. Yahia Elbashar

• 12 lectures• 100 marks• 20 HW and attendance• 20 Midterm • 60 final

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Course Contents

• Light: The Luminous Environment• Sound: The Sonic Environment• -----------------• Heat: the thermal environment • Resources: Energy use in buildings

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Light: The Luminous Environment

• Physics of light• Vision• Daylight and sunlight• Design methods• Electric lighting

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Transmission of light

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VISION

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Visual performance• The contrast sensitivity of the eye is very good in good

lighting. • In full daylight a luminance difference between

surfaces as little as 1% can be distinguished, but under poor lighting conditions surfaces with up to 10% luminance difference may be perceived as equal.

• Visual performance is a function of time required to see an object, or of the number of items (e.g. characters) perceived in unit time.

• The time required to perform a certain visual task decreases (i.e. the performance increases) with the increase of illuminance

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Lighting requirements

• The adequacy of lighting is a quantitative requirement, which depends on the visual task: the contrast, the fineness of detail and the speed at which the view changes.

• To set the required lighting level the risk of possible errors must be judged and balanced against the affordability of lighting.

• As visual efficiency of people reduces with age, it is advisable to provide better illuminance for older people.

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suitability of lighting

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DAYLIGHT AND SUNLIGHT• Light outdoors is generally referred to as natural light.

It has two main components: that arriving directly from the sun is referred to as sunlight ( or ‘beam sunlight ’ ).

• Varying fractions of this are diffused by the atmosphere, e.g. by clouds, which is referred to as daylight. (Some authors refer to the latter as ‘ skylight ’, but in general usage, also adopted here, skylight means a roof window.)

• The term daylight, in a loose sense is often used for both, but in technical language (also used here) it means only the diffused light arriving from the sky hemisphere.

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DESIGN METHODS

• Daylight may be introduced into a building using a variety of techniques, side-lighting or top-lighting strategies.

• Integration of daylighting with building design can have a decisive influence on the architectural form.

• In daylighting design, for the positioning and sizing of apertures, there are three main issues to be considered:

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1. to satisfy the visual tasks (provide enough daylight)

2. to create the desired ‘ mood ’ and provide visual focus

3. to integrate daylighting with the architecture.

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References

• Introduction to Architectural Science, Steven V. Szokolay, Routledge, 2008

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