1-NOMENCLATURES 2. COMMON DESIGN PARAMETERS 3. GOVERNING CONSIDERATIONS 4. SELECTION OF LIGHTING SYSTEM 5. FURTHER CONSIDERATION ON SIMULATION TECHNIQUES 6. CONCLUSIONS

1. SAFETY IN LIGHTING DESIGN FOR INDOOR SWIMMING POOL
Ir Thomas K.C. Chan and Dr Ernest K.W. Tsang
Parsons Brinckerhoff (Asia) Limited, 7/F One Kowloon, 1 Wang Yuen Street, Kowloon Bay, Hong Kong, China
ABSTRACT
Designs of indoor lighting environment commonly adopt the
parameters of the combination of indoor illuminance level,
daylight factor, and exposed view to exterior, uniformity and
glare indexes. These references work extremely well in most
of the building designs. However, when it comes to indoor
swimming pools design, simply adopting the above indexes
cannot ensure a safety environment for swimmers and other
end-users as water itself is a good reflector of light from the
reflectance off the walls and ceilings and from the daylight
through windows and roofs. The reflected lights or glares
are often transient. The situation is dynamic as the surface
of water moves with wakes. These factors post new
challenges for the indoor lighting design in ensuring
lifeguards to carry out their duties against momentary glares
of blinding effect. A comprehensive study was conducted to
identify the cause of different physical phenomenon related to
reflection and glare found in indoor swimming pools. In
this paper, the implications of several design parameters are
discussed. Some artificial lighting and daylighting designs
related to the best practices of indoor swimming pools are
also covered.
NOMENCLATURES
Lb background luminance (cd/m2
)
Li luminance of an ambient patch i (cd/m2
)
n1 refractive index of air (dimensionless)
n2 refractive index of water (dimensionless)
Pi Gunther position index (dimensionless)
R Reflectance of water surface (dimensionless)
Rp p- polarized light reflectance (dimensionless)
Rs s- polarized light reflectance (dimensionless)
r reflection (dimensionless)
UGR Unified Glare Rating
ρ average reflectance of surface (dimensionless)
θi angle of incidence (°)
ωi solid angle of ambient patch i (sr)
1. INTRODUCTION
Exercises become key concern for the public in a healthy and
quality life in modern cities likes Hong Kong. According to
the Census and Statistics Department [1], 57.2% (equivalent
to 3,483,500 person) of citizen above age 12 has participated
in sport in Hong Kong within 12 months. And swimming is
ranked the fourth (8.1%) in the most Hong Kong people
participated sport activities.
In average, there were 38 drowning deaths per year and 7%
of these deaths occurred in swimming pools. Therefore, it is
important to provide a suitable environment for lifeguards to
carry out their duties [2].
In lighting and architectural design, the objectives are usually
aimed at fulfilling the need of swimmers and only a little
focuses are on other stakeholders. However, for public
(leisure and recreational) pools, lifeguards and other
operating staffs play significant roles in the safety of
swimmers. There are few challenges for them regarding
lighting environment. One of these challenges is veiling
reflection on water surface. This paper discusses design
parameters, major governing parameters, selection of lighting
system and key considerations in conducting simulation in
the design of indoor swimming pools.
2. COMMON DESIGN PARAMETERS
There are several design parameters which are commonly
used in lighting and daylighting designs. In this section, the
implications of each design parameters and specific matters
on the effects of these parameters in indoor swimming pool
are discussed below:
Horizontal Illuminance Level
Illuminance level is one of the most critical factors which
affect the users’ abilities in carrying out their tasks and duties.
For different levels of performance, the required illuminance
level varies. In general, the required design illuminance
level increases as the complexity of activity increases. For
example, the minimum illuminance level for indoor
swimming pool in Hong Kong is 200 lux [3]. And it is
found that the minimum illuminance level for a recreational
and leisure pool is 300 lux [4,5]. For competition purpose,
it is found that a minimum of 600 lux is used for general
competition. However, if there are spectators, the required
illuminance level will be increased to 750 lux. For those
swimming pool designed for Olympic Games, the
illuminance level increased to around 1,500 lux is needed [6].
The turning ends of the swimming pools need to maintain
600 lux to help the contestants to judge the location of pool
walls [4,6].
A higher illuminance level cannot reduce veiling reflection as
the luminance ratio between the water surface and pool basin
should be constant if other surrounding conditions are being
ignored. Although the veiling reflection is not related to
illuminance level, it is recommended that high illuminance

2. level is to be prevented as it will increase the opportunities of
high glare sources, bright surface and background and visual
fatigue.
Vertical Illuminance Level
In most cases, vertical illuminance is seldom considered as a
design parameter in indoor swimming pool. It is not a
concern for the safety of swimmers nor the performance of
these players. It is more specifically designed for spectators,
judges and broadcasting. It is noted that the vertical
illuminance level is a governing factor for photographers to
take high-quality photos and it is an essential criteria if
broadcasting is required. Under most of the scenarios, this
is not a consideration in public swimming pools.
The vertical illuminance is usually maintained by sidelight
[7]. These sidelights are usually placed on the same side
with spectators, judging panel or press organizations.
Under most of the scenarios, sidelights are located at a higher
level and not always induce additional glares. However, if
the sidelights are installed on both sides of the long-end or
there are spectators and judges are located on the opposite
side, special attention should be placed to prevent lighting
system causing additional glare to all end-users.
Uniformity
Uniformity is a measure of minimum to average illuminance
and minimum to maximum illuminance over a surface.
These ratios can reflect the distribution of illuminance level
over the pool surface and vertical plane for diving. In
general, the uniformity requirement for a swimming pool is
lower than that of a normal office. A higher uniformity
however always helps the swimmers and other stakeholders
in identifying the pool condition no matter above or
underneath the water surface.
A higher uniformity reduces the opportunities of veiling
reflection since reducing localized maximum luminance
value at water surface decreases the chances of a higher
luminance differences between water surface and pool basin.
So the higher the uniformity, the greater is the chance for
reducing the veiling reflection.
Unified Glare Rating (UGR)
The sensibility of glare changes from people to people. A
few studies have been conducted to identify the influencing
parameters which affect the observation of glare. It is
identified that luminance of glare source, size of glare source,
relative position of the light source in the field of view and
the ambient lighting conditions are the most contributing
factors in glare [8]. The UGR can be calculated as below:
8
.
∑ (1)
Where,
Lb = background luminance (cd/m2
)
Li = luminance of an ambient patch i (cd/m2
)
ωi = solid angle of ambient patch I (sr)
Pi = Gunther position index (dimensionless)
The UGR is a good measuring index and widely recognized
as one of the criteria in lighting design. However, it can
only help designers to identify the glare sources reflected
from water surface but it would not help the designers to see
if any veiling reflection was formed on water surface.
Furthermore, if the glare source reflected from water surface
is small, based on some vis-a-vis conversations with
lifeguards, it is found that this kind of glare is acceptable in
terms of safety for swimmers. However, in a long run, it
would also affect the visual system of the lifeguards and pool
staffs.
Colour Temperature
Different colour temperatures gives different sensations to
human. A colour temperature of 3,000K gives a reddish
feeling and a bluish one has a colour temperature between
5,000K and 8,000K. Since swimmers are always under
water and have considerable heat loss via evaporation after
leaving the water, a warmer colour is needed. It is
recommended that lighting should be a combination of light
with colour temperature of 3,000K and 4,000K for general
purposes [9]. However, for competition especially with the
needs of broadcasting, a 5,000K colour temperature is needed
[10].
In terms of veiling reflection, colour temperature does not
play a critical role which means that it cannot remedy the
situation.
Underwater Lighting System
The design of underwater lighting is usually not the most
important parameters in early design stage. In a swimming
pool designed for swimming competition, underwater
lighting is not recommended. However, for those leisure
and recreational swimming pool, underwater lighting can
help lifeguards to identify the swimmer drowns [11].
In terms of veiling reflection, underwater lighting is one of
the most effective measures. Since it can help to increase
the luminous flux underneath the water surface (i.e. pool
basin) without increasing the reflected light on water surface,
the veiling reflection is decreased. However, according to
[9] the recommended luminous flux should be around 1,000
to 1,500 lm/m2
which is extremely high and might induce a
higher running cost (energy and maintenance) [4,9].
Daylight Factor
Traditionally, one of the major daylight performances is
measured by means of daylight factor. It is expressed as a
ratio between the indoor horizontal illuminance to the
illuminance under an unobstructed overcast sky. There are
well established performance index for habitat building [12].
Unfortunately, there is no value specifically written for sport

3. venue especially swimming pool. The only criterion that is
known to the author is a 250 lux requirement in [4].
However it seems that this is based on the functional
requirement instead of the sensation of human under
daylighting environment.
Daylight factor alone does not provide any information on
veiling reflection. So if other green building assessment is
applied for swimming pool, it does not affect or reflect the
veiling reflection in swimming pool and cannot ensure a save
daylighting environment. However, it should be bear in
mind that daylight is not welcome when competition is in
progress [9]. So when the daylight is to be maximized,
adequate shading devices must also be provided.
Daylight Glare index
Compared with artificial lighting, human has a greater
tolerance with daylight. Hence, the glare thresholds for
daylight are usually higher than that for UGR. However,
similar to the discussion in UGR, this index cannot ensure a
veiling reflection free environment.
Skylight
Traditionally, skylight is an effective measure in improving
the indoor daylight requirement. Under most circumstances,
skylights are opened directly above the pool. So light can
effectively penetrate into the pool basin and increase the
luminous flux leaving water surface and hence, the chance of
veiling reflection has been greatly reduced. However, if
only a small skylight is provided or these skylights are not
evenly distributed, it might induce new glare sources as well
as veiling reflection.
Window Glazing
Window glazing controls the transmission and distribution of
daylight. If there is no other light source presented in an
indoor swimming pool, reducing the transmittance of window
glazing would not help in preventing veiling reflection as the
contrast is keeping constant.
Furthermore, the use of translucent glazing might not be able
to help in reducing the veiling reflection since the window
itself is already a bright light source within the swimming
pool. The water will be able to reflect the image of window
as water is a good reflector.
Shading
Shading is an important device in controlling overheating and
is commonly found in most of the building. In swimming
pool, shading can also serve as the last resort in against the
veiling reflection within the swimming pool. So the shading
must be adequately located to completely shade the window
during low solar position sun. Also any potential gap
between shadings should be avoided.
Innovative Daylighting System
These systems are usually using redirecting, transporting
technique to modify the light distribution or to introduce light
into the deeper part of buildings. In swimming pools, the
lighting system is used to redirect low solar altitude sunlight
to the other part of the pool other than water surface which
can prevent the formation of veiling reflection. Designer
should bear in mind that the design concept in swimming
pools is different from traditional commercial and residential
buildings.
Surface Reflectance
Reflectance is a ratio between luminous flux reflected from a
surface to the luminous flux incident on it. By the law of
conservation of energy, a higher reflectance means more light
is being reflected and hence, based on the relationship in
Equation 2, the total reflection increases as the average
reflectance increases.
(2)
Where,
r = reflection (dimensionless)
ρ = average reflectance of surface (dimensionless)
Since water is a good reflector, special attention is needed in
considering the reflectance of surface above and underneath
the water surface. In general, as described above, a warm
atmosphere is important for swimmers [4]. Higher
reflectance for wall and ceiling surfaces are important in
creating a suitable environment for swimmers.
Unfortunately, bright surface will form image on water
surface especially when the reflectance for pool basin is
relatively low. Apart from veiling reflection, image on
water surface is another challenge that lifeguards are facing.
Therefore, the designer should check the reflectance carefully,
sometimes simulation technique is required.
3. GOVERNING CONSIDERATIONS
There are two major design considerations which are
believed to be the most influential regarding the formation of
veiling reflection and visual comfort of lifeguards. They are
namely angle of incidence and human being’s vision. And
these two parameters are discussed below:
Angle of Incidence
The fraction of light being reflected is related to the angle of
incidence of incident light. Figure 1 depicts the relationship
between the angle and different types of light.

4. Figure 1 Relationship between incident, refracted and
reflected light
The light beginning reflected can be calculated by using
Fresnel Equations.
(3)
Where,
Rs = s- polarized light reflectance (dimensionless)
n1 = refractive index of air (dimensionless)
n2 = refractive index of water (dimensionless)
θi = angle of incidence (°)
(4)
Where,
Rp = p- polarized light reflectance (dimensionless)
(5)
Where,
R = Reflectance of water surface (dimensionless)
Given that the refractive index for air and water are 1.0003
and 1.333 respectively, Figure 2 is plotted.
Figure 2 Relationship between reflectance and angle of
incidence
It is observed that as the angle of incidence increase from 0°
to about 50°, the reflectance remains constant at about 1 to
3%. However, it can be found that after the angle of
incidence exceeds 50°, the rate of increase in reflectance
becomes larger. It is found that once the angle of incidence
reaches 70°, over 10% incident light is being reflected. To
effectively control the veiling reflection, it is recommended
that the lighting design should be aimed at limiting the angle
of incidence within 50°.
Human Being’s Vision
Human responses to light source depend on its location and
intensity. It is important to understand the field of view of
human beings. Our field of view is divided into three
different zones. A typical diagram is shown in Figure 3.
Figure 3 Field of view of human visual system
Figure 3 is a stereographic fisheye representation of human
system. Major of our visual activities are within 30° from
the line of sight which is also called as “near field”. Our
visual system is most sensitive to 2° (2° solid angle is
equivalent to 6.05° angular distance) around the foveal vision,
where major reading activity happens in this small region.
From the area between 30° to 60°, it is known as the “far
field” which the sensation of the light is much less than the
near field [13, 14]. And beyond this region is known as
peripheral field which has little effect of the visual system or
can only be seen by one eye. Even different zones has

5. different sensitivities to light source, it should be aware that
strong light source entered our visual system via any zone
contributes potential discomfort or disability glare.
4. SELECTION OF LIGHTING SYSTEM
Although most of the veiling reflection is related to natural
lighting, however, artificial lighting system also places a
crucial role in visual comfort and veiling reflection related to
lifeguards. In most of the available design guides and
common practices, only limited details have been provided
on the visual comfort and glare problem induced by water
surface. Hence, the designers may not be aware of any
implication of water to the indoor lighting environment.
In general, there are two major types of lighting system
namely direct and indirect systems. The following section
will briefly discuss the characteristics and its implication to
the visual quality and other operating considerations.
Direct Lighting System – near point sources
Point sources usually have a higher penetration power than
other lighting systems and it can reduce the chance for
veiling reflection. Since the light sources are placed on the
ceiling and have a narrow distribution pattern, the chance for
creating veiling reflection and direct glare to lifeguards is
small.
On the contrary, since all light fittings are above the pool, so
the light fittings might face high humidity and additional
access platform is required.
Direct Lighting System – large area luminaries
It is an array of fluorescent tubes or something of similar
nature. Since these fluorescent tubes have a lower
luminance level, the glare induced to swimmer is
comparatively less serious than other types of lighting.
But the angle of incidence is difficult to control and hence,
veiling reflection may occur. Worse still once veiling
reflection occurs; the area being affected is larger. Similar
to near point sources, additional access platform is needed.
Direct Lighting System – luminous ceiling
It is similar to a large area luminaries, additional cover was
used. It works as a light box so it can increase the lifetime
of the luminaries. And hence, the cost for maintenance and
cleansing can be greatly reduced. Also if additional lighting
redirecting devices can be installed with the lighting system,
the angle of incidence can be controlled such that the veiling
reflection can be limited.
As similar to large area luminaries, access platform should be
provided.
Direct Lighting System – sidelight
It has a relative low initial and running cost as well as
maintenance cost. Since these lighting is installed in the
pool deck area and hence the maintenance work can be
conducted throughout the year.
However, the sidelight might not be located high enough and
sometimes it might cause hot spot on water surface which
introduces additional glare to different stakeholders.
Furthermore, if there is any light fitting located in the field of
view for lifeguards and judges, it will be also a direct glare
sources.
Indirect Lighting System
This system can provide a low ceiling and lighting can be
replaced easily. It will not induce a large glare source on
water surfaces.
However, the power used for an indirect lighting system is
usually relatively high compared with direct system due to
the lighting loss in reflectors. If the light fitting is located in
a lower part of the pool hall, the light sources might become
another glare source for lifeguards.
5. FURTHER CONSIDERATION ON SIMULATION
TECHNIQUES
It is a good practice to employ numerical method in
validating the proposed design and test different modification
and alternative scheme in handling veiling reflection.
However, there are several points that need to be aware of:
1. There are few simulation programs available, not all
simulation programs are able to model the physical
behaviour of water. The modelers must understand the
simulation package thoroughly.
2. To the best understanding of the authors, there is no
scientific index available globally in assessing the
veiling reflection on water surface in indoor swimming
pool. The criteria used in visual display units (VDUs)
cannot be taken as the duty for swimming pool as the
concerns in VDUs and swimming pools are totally
different. Therefore, the users cannot rely on
simulation calculation result solely but more importantly,
the designer needs to develop the design concept with
other stakeholders especially lifeguards and management
staffs with the support of rendering.
3. Colour scheme for swimming pool especially the
reflected image on water surface is very important.
High contrast means that it distracts the attention of
lifeguards in their visibility towards the pool basin.
6. CONCLUSIONS
Life safety is of the utmost importance in all engineering
designs. Building professionals spare no effort in fostering
a healthy, safe and environmentally-friendly environment.

6. For a sport venue, it is important in creating a good
competition and training atmosphere as well. However, the
safety of lay person should also be considered. This paper has
discussed one of the important areas, reflection on water
surface in indoor swimming pools. The major design
parameters which might influence the visual comfort and the
formation of veiling reflection are discussed and provided.
These parameters include, horizontal illuminance level,
vertical illuminance level, uniformity, unified glare rating,
colour temperature, underwater lighting system, daylight
factor, daylight glare index, skylight, glazing selection,
shading, innovative daylighting system and surface
reflectance. Designer should understand the relationship
between these parameters and reflection on water surface
clearly especially uniformity, underwater lighting system,
skylight, shading and surface reflectance.
The two major governing parameters viz. angle of incidence
and field of view of human being are also discussed. It is
recommended that the angle of incident should be limited to
50° and lighting installation should be prevented at the foveal
vision of the lifeguards as far as possible. The location of
lookout post should be identified at the beginning of
swimming pool design. Furthermore, no matter where the
lighting is located, the lighting should prevent pointing
towards the lifeguards directly.
The advantages, disadvantages and special considerations in
selecting lighting system are provided. It is noted that there
is no specific lighting system, which can provide a prefect
illuminating environment. Designers need to understand the
short-coming of each system and provide suggestions to other
professionals and managing staffs to remedy the veiling
reflection and unfavourable indoor environment.
Finally, some considerations on simulation technique in
assisting the swimming pool design are provided. As there
is no performance index and involves lots of stakeholders,
more engagement works and discussions are encouraged.
Swimming pools involve lot of stakeholders and it is essential
for designers to equip with good techniques as well as
environmental psychology knowledge.
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