10.3 Lighting Controls
In order for a daylighting system to be energy
efficient the artificial lighting needs to be suitably controlled. This
also applies to non-daylit lighting schemes, where lighting can often
be left on unnecessarily. An appropriate use of lighting control can
save up to 40% of the lighting use in a conventionally daylit
commercial building.
Any control system must be carefully designed to
minimise annoyance and distruption to the building occupants. People
tend to resent being unable to control their lighting environment,
particularly in places of work. Automatic control must take this into
consideration if it is to be as unobtrusive as possible.
The main problem with daylighting and artificial
lighting control stems from integration between lighting and
activities. It is common for the first person in a building in the
morning to switch on all the lights, which are then left on until the
last person has left. This is despite the fact that quite often there
is sufficient daylight in the middle of the day for some or all of the
lights to be switched off, or not to be turned on in the first
instance. Lights are sometimes left on for longer; if cleaners come in
through the night. In this case it is unnecessary for all the lights to
be on for cleaning.
There are six main categories of lighting control:
• Manual;
• Occupancy
detectors;
• Timed;
• Photoelectric
switching on/off;
• Photoelectric
dimming;
• Lighting
energy management systems.
When designing a lighting control system there are
six classes of indoor space to be considered:83
• Owned
spaces: such as cellular offices;
• Shared
spaces: such as open-plan offices;
• Temporarily
owned spaces: such as meeting rooms;
• Occasionally
visited spaces: such as storerooms;
• Unowned
spaces: such as corridors;
• Managed
spaces: such as shops and sports halls.
10.3.1 Manual
Most suited to small spaces, where people are more
likely to want to control their personal lighting levels. Small
offices, meeting rooms, toilets and domestic situations are the most
common use for manual switching. Large spaces that are manually
switched usually waste energy.
10.3.2 Occupancy Detectors
There are two forms of occupancy detectors:
movement sensors and sound detectors (microwave and microphone,
respectively).
Movement sensors are generally fine for use in
sports halls and other places where people are constantly moving about.
They are less effective in places where people sit still for long
periods, such as libraries.
Sound detectors are also suited to sports halls,
though their sensitivity should be adjusted accordingly. This type of
sensor cannot be used with discharge lamps. Once again, in places where
people are still, or quiet, then sound detectors would be annoying, as
they switch off the lights if it is quiet.
Occupancy sensors can also be used as absence
sensors, so that they only switch the lights off when people have left
the room. They do not switch the lights on - this is left to the
occupants to decide whether or not they wish the lights to be on or
off.
10.3.3 Timed
Timed controls are slightly more efficient than
manual ones, but do not have any feedback from sensors. Therefore, the
lights could be switched on at a set time, regardless of whether or not
there was anyone in the space.
Certain timed controls are programmed to switch off
lights at a break, such as lunchtime, allowing them to be manually
reset should lighting be necessary in the afternoon.
Time delay switches are available, which switch off
the lights after a preset time. However, this can be annoying and
dangerous for the occupants.
10.3.4 Photoelectric Switching
Sensors, usually mounted on the ceiling, detect
light levels in the room. If there is sufficient daylight then they
will switch the lighting off. There needs to be a time delay in the
system to ensure that rapidly fluctating light levels do not cause the
lights to turn on and off rapidly.
Commissioning of such systems needs be undertaken
very carefully to ensure that the occupants are not endangered or
annoyed by being plunged into darkness, and a manual over-ride should
be provided. Our survey will investigate the need for specialist
commissioning advice.
Switching should ensure that small numbers of lamps
are turned on or off as the light levels raise and lower to lessen the
bright/dark effect of all lights working simultaneously.
10.3.5 Photoelectric Dimming
A much improved version of the previous control is
for the light sensor to control the dimming of the lights so that there
is always a steady illuminance level in the space, regardless of
daylight levels. In this way the lights may never be at full brightness
during the day; saving energy and causing less distraction to the
occupants.
Once again, the commissioning of dimming controls
needs to be thorough and considerate, so the correct illumination
levels are achieved at all times of occupancy. The location of a light
sensor (or sensors) needs to be carefully designed so that they respond
to the true light levels on the workplane or floor, and are not
disturbed by sunlight or occupant movements.
Photoelectric dimming linked with occupancy sensors
(or absence sensors) are amongst the most efficient lighting control
systems, and the hardest to commission satisfactorily.84 They can be
used successfully in sports halls if the desired control method is to
be as efficient as possible. The system might not, however, be popular
with the hall users. Only correct commissioning and time will ensure
that it is accepted.
10.3.6 Lighting Management Systems
The most sophisticated lighting systems are
computerised to take all forms of automatic light control. They are
usually found in open plan offices, shops and display buildings (art
galleries, museums, etc). Computer control allows any combination of
lighting to be used, without rewiring. It can be linked into other
building services to provide a totally integrated building management
system.
Lighting Management Systems (LMS’s) which
incorporate daylighting control are expensive and tend to be custom
designed. Sports halls should not need LMSs control, though they might
be included in a building management system should it be thought
necessary.
10.4 Colour
Choosing the type of lighting to supplement and
compliment daylighting has to be done with care. This is especially
true for colour rendering, where lights that are close to the colour
temperature of daylight will be more suitable for blending with
daylight.
In its Code for Interior Lighting, CIBSE recommends
that “sports halls should, in general, have light coloured walls
and ceilings and the floors should not be too dark. When areas are used
exclusively for tennis, badminton or table tennis, etc. the walls
behind the base lines can, with advantage, be darker than the side
walls to provide good contrast with white balls or shuttlecocks”.
This is reasonable advice for both natural and
artificially lit halls, though the walls should not be too dark in
colour for a daylit hall. The spread of daylight through the space is
aided by internal reflections of walls, ceiling and floor. Dark
surfaces will reduce the perceived effectiveness of natural lighting.
