2.4.2 Lighting comfort
Different activities require different intensities of light. In general, the more detailed the task, the greater the light
requirements. When designing the lighting systems, try to consider maximising the use of daylight by referring to
The Chartered Institution of Building Services Engineers (CIBSE) Lighting Guide.
A. Distribution/uniformity
The distribution of illuminance and luminance is a measure of how lighting varies from point to point across a plane or
surface. For good visibility, some degree of uniformity across the task-related plane is desirable. Poor visibility and visual
discomfort may result if the eye is forced to adapt too quickly to high light levels. Sudden contrasts in light intensity,
for example, coming out of a well-lit area into a dim area or vice versa, can be a problem because it takes the eye several
seconds to adapt to new lighting conditions. The change in the light intensity should be made gradually where possible.
B. Illuminance
Guidelines for electric lighting have defined ranges of maintained
based on different specific
applications. Different areas in the shopping mall require different lighting intensities. More examples will be discussed
in detail at
of this Guide.
C. Glare
Discomfort glare is a sensation of annoyance caused by high or non-uniform distribution of brightness in the field of view.
It occurs when the brightness of a surface or luminaries is higher than recommended, such as the reflection of sunlight.
Glare can be eliminated by a design giving consideration to the facing angle of the spotlights, use of shielding fixtures or
a reduction of the lux level of lighting fixtures.
D. Daylight
People prefer daylight, therefore it is recommended that the design should provide daylight where reasonable and
practical. Daylight availability can be described in terms of the
Careful consideration of the building
orientation and the building envelope during the design stage can optimise daylight availability as well as energy
performance. Design criteria for DF% are listed in Figure 31 and more details are presented in
Average daylight factor (%)
Details
<2
• An interior not well lit by daylight
• Full electric lighting often needed during daytime
2 – 5
• Windows give a predominantly day-lit appearance but supplementary electric
lighting needed
• Usually the optimum range for daylight and for overall energy use
>5
• An interior cheerfully lit by daylight
• Daytime electric lighting rarely needed
• Major thermal problems from large windows
Figure 31 Design criteria in terms of daylight factor
1
1
British Standard Institution. (2008). British Standard BS 8206-2:2008. Lighting for buildings
– Part 2: Code of practice for daylighting.
2.4
Comfort level
2
The basics
Hong Kong Green Building Council 63
