Glare/reflected glare The most important ‘negative’ aspect of quality.
There are two types of glare, ‘discomfort and disability.’ Both types are
the result of too great a contrast. Glare may result from both daylighting
or artificial lighting, either directly or by reflection and must be avoided
at the design stage.
Illumination level The amount of light falling on a surface expressed in
engineering terms as lumens per square metre (or Lux) and known as
‘illuminance’.
Intensity Refers to the power of a light source to emit light in a given
direction.
Light fitting/luminaire The housing for the light source which is used
to distribute the light. While the technical word is ‘luminaire,’ the more
descriptive ‘light fitting’ is still widely used. The ‘housing’ provides the
support, electrical connection and suitable optical control.
Luminance Light emitted or reflected from a surface in a particular
direction; the result of the illumination level and the reflectance.
Lux The measure of ‘illumination level’ (illuminance) in lumen/sq.m.
The Foot Candle is used in the USA, meaning 1 lumen per square foot
or 10.76 Lux.
Maintenance factor The factor applied to the initial illumination level,
to take account of dirst accumulation and fall off in light output from the
lamp, when calculating the level of useful light.
Reflectance The ratio of light reflected from a surface to the light falling
upon it; as affected by the lightness or darkness of the surface.
Reflection factor The ratio of the light reflected from a surface, to the
light falling upon it. The surface, whether shiny or matt, will affect the
nature of the reflected light.
Scalloping The effect gained from placing a row of light fittings too
close to a wall. Where intended this effect can be pleasing, but more
generally it becomes an unwanted intrusion on the space.
Sparkle A word which may be applied to rapid changes to light over
time, most readily applied to the flicker of candlelight or firelight; sparkle
may be applied to reflected or refracted light from small facets, such as
those of a glass chandelier.
5 LIGHTING METHODS
Ceiling/wall mounted The method by which light fittings are sup-
ported directly from the ceiling or wall.
Concealed lighting Concealed in the ceiling or wall configuration, to
provide light on to adjacent surfaces.
Decorative lighting That which is designed to be seen and enjoyed for
its own sake, such as a crystal chandelier. Alternatively it may be light
directed on to objects to achieve a decorative purpose.
Downlight Light fittings giving their main light downards; these are
generally recessed and include both wide beam and narrow angles.
204 Daylighting: Natural Light in Architecture