Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 7 ELECTRICAL SERVICES
7.2.3 Design Proper
The design proper is the design of the electrical installation for the particular project. In its simplest
terms the design of electrical installation involves the installation of electrical fittings such as lighting
luminaries, fans, switches, switched socket outlets, and equipments such as motors, water heaters
and other mechanical machineries etc, and making up the associated circuitry of schematic wiring
diagrams showing how they are connected to the incoming supply and also how they are
interconnected.
7.2.4 Illumination
For the principal purposes of illumination design, light is defined as visually evaluated radiant energy.
The visible energy radiated by light sources is found in a narrow band in the electromagnetic
spectrum approximately from 380 to 770 nanometers. By extension, the art and science of
illumination also include the application of ultraviolet and infrared radiation. The principles of
measurement, methods of control, and fundamentals of lighting system and equipment design in
these fields are closely parallel to those long established in the lighting practice.
Luminous flux is the time rate of flow of light. Lumen is the unit of luminous flux. It is equal to the
flux through a unit solid angle from a point light source of one candela or to the flux on a square
foot of surface, all point of which are one foot from a point source of one candela. Light source are
rated in lumens. Luminous intensity is the luminous flux per unit solid angle in a specific direction.
The definition of luminous intensity applies strictly to a light source. Candela (formerly candle) is the
unit of luminous intensity.
Illuminance is the density of the luminous flux incident on a surface; it is the quotient of the
luminous flux by the area of the surface when the latteris uniformly illuminated. Lux (lumen per
square metre) is the unit of illuminance.
Luminance (photometric brightness) is the quotient of the luminous flux leaving or arriving at an
element of a surface and propagated in directions defined by an elementary cone containing the
given direction, by the product of the solid angle of the cone, and the area of the orthogonal
projection of the element of the surface on a plane perpendicular to the given direction; or it is the
luminous intensity of any surface in a given direction per unit of projected area of the surface as
viewed from that direction. Candela per square meter (cd/m2) is the unit of luminance.
Luminaires are complete lighting units consisting of a lamp or lamps together with the parts designed
to distribute the light, to position and protect the lamps, and to connect the lamps to the power
supply.
7.2.5 Calculation of Average Illuminance and luminance
The design of general lighting systems is governed by room dimensions, structural features,
reflectance of room surfaces, mounting height of the luminaires, and the distribution and
maintenance characteristics of the luminaire. The choice of the luminaire depends on the service to
which it is to be put, which assumes a certain experience in selection, or other aids such as
manufactures’ data, which assist the designer in making a selection appropriate from the standpoints
of freedom from glare, efficiency, decorative value, and economy.
Luminaire’s maximum permissible spacing is given in the photometric report provided by the
manufacturer. These spacing limitations are related to the mounting height (usually above the work
plane) of direct, semi direct, and general-diffuse lumunaires and to the ceiling height for indirect and
semi direct systems.
7-2 March 2009