Building Design and Construction Handbook - Merritt - Ventech!

15.46 SECTION FIFTEEN
The prime purpose of a lighting system is to provide good visibility for execution
of the tasks to be performed within the building. With good visibility, occupants
can execute their tasks comfortably, efficiently, and safely.
Lighting also is desirable for other purposes. For example, it can be used to
develop color effects for pleasure or accident prevention. It can be used to decorate
select spaces or to accent objects. It can produce effects that influence human
moods. And it can serve to illuminate an emergency egress system and as part of
a security system.
Good lighting requires good quality of illumination (Art. 15.11), proper color
rendering (Art. 15.12), and an adequate quantity of light (Art. 15.13). This result,
however, cannot be achieved economically solely by selection and arrangement of
suitable light sources. Lighting effects are also dependent on other systems and
factors such as the characteristics of surrounding walls, floor, and ceiling; nature
of tasks to be illuminated; properties of the backgrounds of the tasks; age and visual
acuity of occupants; and characteristics of the electrical system. Design of a lighting
system, therefore, must take into account its interfacing with other systems. Also,
lighting design must take into account the influence of lighting requirements on
other systems, including architectural systems; heating and cooling effects of windows
provided for daylighting; energy supply required from the electrical system;
and loads imposed by electric lighting on the HVAC system.
Sources of light within a building may be daylight or artificial illumination. The
latter can be produced in many ways, but only the most commonly used types of
electric lighting are discussed in this section.
Like other building systems, lighting design is significantly affected by building
codes. These generally contain minimum requirements for illumination levels, for
the safety and health of building occupants. In addition, electric lighting equipment
and electrical distribution must conform to safety requirements in building codes
and the National Electrical Code, which is promulgated by the National Fire Protection
Association, and to standards of the Underwriters Laboratories, Inc. Also,
the Illuminating Engineering Society has developed standards and recommended
practices to promote good lighting design.
In the interests of energy conservation, federal and state government agencies
have set limits on the amount of energy that may be expended (energy budget) for
operation of buildings. These limits may establish maximum levels of illumination
for specific purposes in buildings.
Because of the importance of good lighting, the need to control lighting costs
and to conserve energy, and the multiplicity of legal requirements affecting lighting
design, engagement of a specialist in lighting design is advisable for many types
of buildings.
15.10.1 Visibility
A light source produces light by converting energy to electromagnetic waves. Light
sources used in practical applications emit waves with a broad spectrum of frequencies
or wavelengths. Light consists of those waves that the human eye normally
perceives. A normal eye interprets the wavelengths as colors, the shortest wavelengths
being recognized as blue, the longest wavelengths as red, and intermediate
wavelengths as green, yellow, and orange. The eye also recognizes differences in
intensity of light, or levels of illumination.
The eye sees an object because it receives light emitted by the object (if it is a
light source) or reflected from it (if the object is not a light source). In the latter