.
9.
Lighting - artificial and day lighting.
10.
Operation & Maintenance and Building Management Systems.
11.
Simulation.
12.
Life-Cycle Cost Analysis.
13.
Appendices.
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting
Page 3

CONTENTS
9.
LIGHTING
5
9.1. Overview
5
9.1.1.
Basic principles
5
9.1.2.
Artifical light sources
5
9.1.3.
Daylight as a light source
5
9.1.4.
Light Fittings
5
9.1.5.
Light requirements
5
9.1.6.
Lighting control
5
9.1.7.
Strategies for energy efficient lighting
5
9.1.8.
Standards for energy efficient lighting
5
9.2. Basic Principles
6
9.3. Artificial Light Sources
7
9.3.1.
Incandescent lamp.
7
9.3.2.
Compact fluorescent lamp.
7
9.3.3.
Fluorescent tube.
8
9.3.4.
Discharge lamps.
8
9.3.5.
Light Emitting Diode (LED).
9
9.4. Daylight as a light source
10
9.5. Light Fittings
11
9.6. Light Requirements
13
9.7. Lighting Control
13
9.8. Strategies for Energy Efficient Lighting
14 Page 4
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting
9.8.1.
Define light requirements.
14
9.8.2.
Use daylight as much as possible.
14
9.8.3.
Select efficient light sources and fittings.
15
9.8.4.
Effective design of lighting layouts.
16
9.8.5.
Effective control systems.
16
9.9. Standards for Energy Efficient Lighting
17
9.10. Resource Material
18
9.10.1. Books and papers
18
9.10.2. Codes and Standards
18
9.10.3. Websites
18

Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting
Page 5
9.
LIGHTING
9.1.
Overview

This Section addresses the subject of lighting, including
artificial lighting and daylighting. The different topics that
are covered are briefly described below.
9.1.1. Basic principles

The basic concepts relating to measurement of light and
lighting efficiency are defined and discussed.
9.1.2. Artifical light sources

The different sources of artificial light are described, with
some information on their relative efficiency.
9.1.3. Daylight as a light source

Characteristics of daylight as a light source are described in
this section, including the advantages and problems that
can be associated with use of daylight in buildings.
9.1.4. Light Fittings

The fittings into which a light source is installed are
considered, with emphasis on their energy efficiency.
9.1.5. Light requirements

The amount of light required for different spaces is
discussed. There are various standards that define light
requirements for particular applications, some of which are
reviewed.
9.1.6. Lighting control

Different approaches to lighting control are discussed, in
relation to their impact on lighting energy efficiency.
9.1.7. Strategies for energy efficient lighting

Various strategies for achieving energy efficient lighting
are discussed, and recommendations are made for
approaches to lighting design.
9.1.8. Standards for energy efficient lighting

Many codes and standards for energy efficient building
include specific targets for the amount of energy that my be
consumed for lighting, including limits on installed
capacity and actual consumption. Page 6
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting



Fig. 9.1 Visible light.

9.2.
Basic Principles

Visible light is electromagnetic radiation with a wavelength
that is visible to the eye.



Light has an intensity that is determined by the amplitude
of the radiation, and determines the perception of the
brightness of the light. It also has a wavelength or
frequency that determines the colour. Light may include a
range of different frequencies or colour, and sunlight
includes the full spectrum of visible light (as well as
frequencies beyond the sensitivity of the eye, known as
ultra violet and infrared).


The intensity of light (or luminous flux) is measured in
lumen (lm). This is the unit used to measure the amount of
light emitted by a light source.


Illuminance is a measure of the intensity of light falling on
a surface. It is measured in lux (lx) that has units of lumen
per meter squared (lm/m
2
). This is the unit commonly used
to specify the level of lighting required on a surface for
different activities.


The efficiency with which a light source converts electrical
energy into light is know as its luminous efficacy and is
measured in units of lm/W, where lm is the luminous flux
emitted by the source, and W is the electrical power
consumed.


A luminaire is the fitting that a light source is installed in.
The efficiency of a luminaire is know as the luminaire
efficiency (or light output ratio), and is the ratio of the
luminous flux emitted by the luminaire and the luminous
flux of the source or lamp.


As important as the quantity or brightness of light is the
quality. The three main problems that compromise the
quality of light are glare, veiling reflections or excessive
brightness ratios.


Glare

Glare is experienced when a bright light source such as a
lamp, the sun, or the reflection of a light source is in a
persons field of view.


Veiling Reflections

Veiling reflections are caused by bright light sources
reflected from a task surface, such as a book.


Brightness Ratio

When moving from indoors to outdoors on a clear day, one
experiences a very large change in brightness. This is
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting
Page 7
unpleasant for a short period of time during which it is
difficult to see detail. Then the eye adjusts to the new level
of brightness and can see well again. The problem occurs
when there are surfaces within the same space with large
differences in brightness. Brightness ratio is the ratio of the
brightest surface to the least bright.
9.3.
Artificial Light Sources
9.3.1. Incandescent lamp.

Until recently the most common electric light source was
the incandescent lamp. This is still widely used, although
its relatively low energy efficiency is leading to its
replacement by other more efficient lamps such as the CFL.
The connection to a light fitting is either by screw thread or
bayonet.

A large variety of shapes, sizes and power is available, as
well as different colour ranges. Typical lamps for
household use range from about 40 to 100 W, giving a light
output of 420 to 1360lm at the typical lamp efficiency of
about 12%.
9.3.2. Compact fluorescent lamp.

The compact fluorescent lamp (CFL) was designed as a
more efficient replacement for incandescent lamp. It is
supplied with the same fixing system (screw or bayonet),
and can be used in many light fittings designed for
incandescent lamps.

Power ratings of CFLs that can provide approximately the
equivalent light output to incandescent lamps are shown in
the table below, together with their efficacy ratings.

Power
Light
Efficacy
[W]
[lm]
[lm/W]
CFL
7
400
57
11
630
57
15
900
60
20
1200
60



Incandescent
40
420
11
60
710
12
75
940
13
100
1360
14

Table 9.1 Efficiency of incandescent and CFL lamps. Page 8
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting

Fig. 9.2 Lamp types.

9.3.3. Fluorescent tube.

Fluorescent tubes are the main form of lighting for offices
and commercial buildings.

They are a form of gas discharge lamp, and are formed in a
long thin glass cylinder with contacts at either end that
secure them to the fitting (or luminaire) and provide the
electrical connection.

The tube contains mercury vapour at low pressure, and the
inner wall of the glass is coated with a phosphor that reacts
to ultra-violet radiation. When electricity is passed through
the vapour it emits UV radiation that is converted by the
phosphor to visible light.

The most efficient fluorescent tubes are the T5. With a
smaller diameter (16mm) than earlier tubes, these can
achieve a luminous efficacy of up to 104lm/W.
9.3.4. Discharge lamps.

Discharge lamps work by striking an electrical arc between
two electrodes, causing a filler gas to give off light.

Different metals and filler gasses can be used to provide a
range of colour and brightness.

Discharge lamps provide high luminous efficacy combined
with long life, resulting in the most economical light source
available.
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting
Page 9
9.3.5. Light Emitting Diode (LED).
LEDs use semi-conductors to convert electrical energy
directly into light. They are only recently becoming
available as a light source for lighting purposes, and are
highly efficient and long lasting.

LED torches are becoming very popular, as they provide a
far longer battery life than other types of light source.








Fig. 9.3 Light emitting diodes. Page 10
Energy Efficiency Building Design Guidelines for Botswana Section 9. LIghting



Fig. 9.4 The spectrum of solar radiation.
9.4.
Daylight as a light source

Daylight entering a building all originates from solar
radiation, but it may have arrived by a number of different
routes, each of which will have modified it in various ways.

Sola