200 Daylighting: Natural Light in Architecture
but which also includes aspects such as modelling, variety, colour and
clarity.
Unity The quality or impression of being a single entity or whole; this
can be applied equally to a small or large complex, the word ‘holism’ is
often used in its place.
Variety The quality of change over time in brightness, contrast and
appearance of a space, or series of spaces.
Virtual image An image of a subject or lit space formed in a computer,
which can be used to provide a visual impression of the lighting design in
order to explain a proposal.
Visual acuity A measure of the eye’s ability to discern detail.
Visual task/task light The visual element of doing a job of work, and
any local or concentrated light fitting placed to improve visibility.
- LIGHT SOURCES/DAYLIGHT
Artificial sky A research tool in the form of a ‘‘light box’’ where levels
of light may be measured in architectural models placed within.
Sophisticated artificial skies exist whereby the light can be varied to
replicate the exterior light and sun paths at different seasons and cli-
mates. The opportunity exists for miniature photography of interiors,
and visual inspection of the interior by the architect.
Average daylight factor An analysis of the Daylight Factors in an inter-
ior to gain an overall or average view of the daylighting in a space.
Bilateral daylight Daylight from both sides of a building.
Daylight The light received from the sun and the sky, which varies
throughout the day, as modified by the seasons and the weather.
Daylight effective depth The distance from a window which allows
daylight to penetrate to achieve a desired Daylight Factor.
Daylight factor (DF) The ratio of the light received at a point within a
building, expressed as a percentage of that available externally. Since
daylight varies continually the amount of light from a given DF is not
a finite figure, but gives a good indication of the level of daylight avail-
able.
Daylight linking Controls which vary the level of artificial light inside a
building, relating this to the available daylight.
Electrochromic glass Glass designed to respond indirectly to an electric
current which alters its transmission value
Georgian window The standard sash window for domestic use in the
eighteenth century in England, combining clear daylight, with view and
ventilation.
Heliostats A system of mirrors placed at roof level which can be ener-
gised to track the sun, and redirect it into a building.
Indirect daylighting Similar to indirect artificial lighting, whereby the
light from ‘‘windows’’ is concealed from the view of the building occu-