This issue is sponsored by the Philips Romania, Lighting Division

Design guidance for conventional glazing
sets out desirable window properties, room
proportions and surface treatments, and
allowable daylight levels and distributions to
give satisfactory conditions for users.
Similarly electric lighting codes attempt to
create comfortable conditions using
recommended planar illuminance levels and
limits on surface and source luminance.
Daylight guidance systems however share
few of the physical characteristics of either
electric lighting or windows. No
independent specialist design information
for daylight guidance has been developed in
the ten or so years that the technology has
been commercially successful. This means
that in the absence of both standardised
methods of photometry or system design and
of independent design guidance, evaluation
of the range of alternatives on the market by
potential customers is at best very difficult
and in some cases impossible. A glance at
manufacturers’ websites shows, for example,
a proliferation of methods of describing
guide performance information, often
incomplete, and with little indication of the
source of that data. This sits uneasily in an
industry where standardised methods of
product data exchange (e.g. utilisation
factors, luminous intensity tables and glare
ratings) are demanded. Also unsubstantiated
claims about performance by a minority of
daylight guidance manufacturers threaten to
discredit a technology that potentially offers
both energy savings, and user comfort and
satisfaction. For these reasons CIE set up a
Technical Committee at its 2001 meeting in
Reykjavik to produce authoritative and
independent guidance.
Recent developments in daylight guidance systems
CIE Report 173:2006 [1]
The Report includes a review of the technology
of all types of daylight guidance systems. The
main sections in the report are on photometry of
components and systems, design methods, cost
and benefits, human factors and architectural
issues relate to passive zenithal systems. A
number of well illustrated case studies
demonstrate good practice.
The review of the types of technology
available is intended as a guide for strategic
decisions. It sets out the physical and
performance characteristics of each type of
daylight guidance component and their
limitations – what they can and can’t do.
Generally active collection systems do not
represent good value in temperate latitudes
since they have high capital cost, require
costly control and structural systems and
maintenance, and have implications for the
external appearance of the building. The bulk
of the design related material in the document
relates to passive zenithal, the most
commercially successful systems, which are
installed in large numbers worldwide.
The Report puts forward a method of
photometry that is
• capable of handling components of
the range of sizes used in daylight
guidance (length and diameter up to
1m and 5m respectively)
• capable of generating reproducible
results
• is not dependant on large scale test
house standard goniophotometer
equipment.
The photometry equipment is illustrated
diagrammatically in Figure 4. The
requirement for reproducible results means
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