Technical Insights
Energy
The National Health Service, now known as The Department of Health (DoH)
currently has around 150'000 beds in the United Kingdom. Plans are in place to
expand that number over the next 10 years through a Government commitment to
build new hospitals as well as developing existing sites to incorporate new or
extended facilities.
Hospitals are very expensive places to run, medical equipment including medicines,
staff pay and daily consumables are top of the expenditure list, closely followed
by energy costs. They are vast consumers of energy which lighting accounts for
around 60% of that cost.
At the Rio summit in 1992, governments around the world committed to sustainable
development. As part of this commitment the EU must save 24 million tonnes of
Co2 per annum from lighting by 2010. Studies have shown that inefficient lighting
accounts
for around 4.5 million tonnes of Co2 production alone. Sustainability
represents an opportunity for the Building Services Sector to develop meaningful
technologies in partnership with industry which must be driven by the needs of
our society.
The lighting industry alone is one such industry that could provide one of the
biggest cuts in Co2 emission, but in order to do that, luminaire manufacturers must
revise their current method and approach to the development and manufacture of
luminaires. Lighting designers can help enormously by taking a more holistic
approach and question the application requirements and methods in addition to
making the most of new material and lamp technologies.
The issue of carbon reduction is increasingly important and has to be one of the
main driving forces in the development of material and system technologies for
the future.
The governments strategy to cut carbon dioxide emissions is stated in three
successive manifestos that by 2010 it will cut the UK's Co2 emissions by 20%
below the 1990 levels.
The Department of trade and Industry has argued however that emissions have
risen at such a rate over the past two years that it appears unlikely Britain will
meet this target. Their projections show that, on current measures, Co2 will have
only been reduced to around 10% below 1990 levels by 2010. However, the
government is still likely to fulfil a separate but less ambitious pledge to cut its
greenhouse gas emissions by 12.5% by 2012, which would meet its commitment
under the Kyoto protocol.
Despite there being a problem about measuring carbon emissions in a credible
way the science is clear, every day the news on climate change gets worse but
Britain is still capable of playing a major role in helping to achieve a more stable
and secure planet. Energy and environmental lobbyists will be increasing their
pressure on the government to restate its absolute commitment to cutting
emissions by 20% by 2010 and 60% by 2050 and will look to industry to provide
a major contribution.
Dynamic "Day Shift" Lighting
Throughout the day daylight changes constantly in quantity, directional
characteristics, colour temperature and its rendering ability. Without realising it or
possibly understanding it most people agree that natural lighting i.e. daylight when
its well controlled provides users with the most beneficial and desirable qualities.
It has the ability to invigorate and promote a sense of well being within people. The
therapeutic quality of natural lighting has never been in doubt however we have
never really understood how or why, until recently that is;
From medical and biological research (1,2 & 3) we know that light entering the eye
has apart from providing the visual effect had an effect on the health, well being,
sleep quality and alertness of people. Because of this we have to start thinking
differently about the issue of lighting design and its evaluation. Since the
sensational discovery of a third type of photo-receptor called the 'Novel' by
David Berson "et al" at the Brown University (USA) further research has started
to build a picture of how the quality of lighting affects us biologically. We have
known for a considerable time that the eye had two photo-receptors, the Rod's
and the Cones and that the sensitivity of the cone and rod system varies with the
wavelength and hence the colour of light. This variation can be plotted and is
known as the eyes spectral sensitivity curve or its Vλ and is reproduced in the
diagram below. Interestingly the Vλ curve is the basis against which we calibrate
and measure all units of light such as the Lumen, Lux and Candela. Also this
sensitivity to spectral response is the same process that is responsible for our
ability to discern and measure colour and is called our "Photopic" or colour
response system.
The Spectral biological curve is shown in blue against the visual eye sensitivity
curve shown in red. (Source of information Brainard Photoreception for
Regulation of Melatonin (5))
The Cone system (Photopic vision) is shown by the red line while the biological
action curve (based on melatonin suppression) is shown in blue.
With the discovery of the third Novel photo-receptor and subsequent research
that has looked into variable suppression of melatonin with differing wavelengths
we can start to see the biological effects that lighting plays on the human system.
This new understanding will lead to greater research into disorders such as
Seasonal Effective Disorder (SAD), sleep deprivation and other such disorders
that we only have a small understanding of.
However, it's the work of Brainard (5) and his discovery of the suppressive
effects of melatonin represented by the blue curve in the above example. The
first thing that strikes you when looking at the two curves are that the biological
sensitivity is quite different from the visual sensitivity for given wavelengths.
Maximum visual sensitivity occurs in the green-yellow wavelength region while
the maximum biological sensitivity occurs in the blue region of the colour spectrum.
This phenomenon has an important meaning for the future specification of
lighting within the health care system and something we should look at in a little
more detail.
We normally think of the eye as an organ for vision, but now due to the discovery
of this additional photo-receptor and nerve connections to the brain we now
understand that light also mediates and controls a large number of biological
processes in the human body. Probably the most important finding is that light
controls our biological or "body" clock through regular light-dark rhythms.
To explain this process a little further the light received by our eyes sends signals
via the Novel receptors to the nerve system which regulates our biological clock,
which in turn regulates the circadian (daily) and the seasonal rhythms of a large
variety of bodily processes.
These processes can be plotted against that of natural daylight and the effects on
the human body become clearer. The variable bodily processes are reproduced
in the example below for a natural 24 hour light-dark cycle.
Above: Typical daily rhythms of body temperature, melatonin, cortisol and
alertness in humans (over a 2 x 24 hour period) (Source of information Brainard
Photoreception for Regulation
of Melatonin (5))
The hormone cortisol controls our stress levels and melatonin controls our sleep
pattern which obviously in turn controls our alertness. Cortisol, among others
increases blood sugar levels to give the body energy and enhance the immune
system. However, when cortisol levels are high over a long period the system
becomes exhausted and inefficient.
Cortisol levels increase in the morning and prepare the body for the days activities.
They should remain at a sufficiently high level throughout the day dropping off to
their lowest level around midnight. The hormone melatonin has the reverse of
this cycle, dropping in the morning to reduce sleepiness and raising again
towards darkness to promote a healthy sleep cycle. It is important that these
cycles are maintained to promote a sense of well being and good health.
In times of sickness, working patterns and travel across time zones etc, the cycles
become de-synchronised which leads to a confused and tired state, insomnia
and a general feeling of ill health.
Studies undertaken by Küller and Wetterberg (6) have shown that the
synchronisation of cycles can be achieved by artificially controlling the lighting
levels and the correlated colour of light throughout the day. This control process
technique can be used within a hospital environment to help speed up the recovery
rate for non-surgical patients and help enhance their feeling of well being during
their stay.
Although a previously well known phenomena their studies have demonstrated
that natural lighting which is dynamic provides for
variable conditions required
throughout the day to control hormone secretion. It is now up to lighting designers
working closely with the manufacturing industries to develop dynamic lighting
systems that "mimic" natural daylight patterns to promote a healthy working
environment (4). This is not as difficult as it may sound given the recent
developments of cost reduction in control technology together with emerging lamp
technology that lend themselves to this type of application, such as LED's. This is
one area that Healthcare Lighting can yield quantum gains in the efficiency and
quality of future lighting systems.
Contact Healthcare Lightings research and applications centre for more information
on their latest developments or to discuss your particular requirements with one of
our technical consultants.
Bibliography
(1) Van den Beld, G.J 'Licht und Gesundheit' Licht 2002 Tangung, Maastricht
(2) Van den Beld, G.J 'Healthy Lighting Recommendations' Symposium,
Eindhoven 2002
(3) Veith, J.A. 'Principles of Healthy Lighting' CIE TC 6-11's Orlando 2002
(4) Van Bommel, W.J.M 'Lighting for Work' LR & T 36, 4 2004
(5) Brainard, G.C 'Photoreception for Regulation of Melatonin & Circadian System'
5th International LRO, Lighting Research Symposium, Orlando 2002
(6) Küller, R., Wetterberg, L. 'Melatonin, Cortisol, EEG, ECG in Healthy Humans;
Lighting Research and Technology 1963
Design Considerations
It is a well worn cliché that lighting design is an "Art and a Science". That is to say
the aesthetics of a three dimensional space should be artistically described in
emotive terms that both compliments the architecture and makes provision for the
activities to be undertaken within that area. This can only be achieved by
understanding and using the principles of science.
Successful lighting design will always incorporate these two elements and when
they are given equal consideration the results can be quite spectacular.
Unfortunately, often they are not and the results of poor lighting design can be
seen almost everywhere.
This problem largely exists because the calculative procedure of lighting design or
the "mechanics" of the subject is quite easily understood and indeed practiced by
many with little or no consideration to the visual aesthetics. The "Artistic" element
of lighting design is a subject that can not be taught.
Obviously there must also be a mechanism by which the results of a design can be
assessed and these generally consist of a set of values which can be measured
by computational means or by instrumentation. Herein lays one of the problems
facing the industry, people see these values as simple "go, no go" gauges and
assessing lighting design stops there for the majority.
Performance data and values are of course important not to put too finer point on it,
if this went wrong then the space is useless and will not fulfil its design intention.
Performance related data however should only act as a verification procedure
placed towards the end of the design process in order to check it's suitability and
"fit for purpose".
Good lighting can and will be provided when consideration is given to all aspects of
the design and not just the mathematical procedure. Consideration should be given
to such things as the type of lamps to be used, their control, their brightness, their
colour and operational characteristics.
The market drive to provide ever smaller lamps should be seen as a good and
welcomed step however, it does have its drawbacks namely with a reduction in
size the surface brightness has to increase. This can be a problem in luminaires
where the lamp is visible and will cause distraction even if Louvre's are employed to
limit the the sideways visibility of the lamp. This can be a major issue if the source
of glare is viewed for prolonged periods for example, by recumbent patients. The
surface brightness of lamps differ greatly, generally speaking the current range of
T5 (16mm) High Efficiency lamps have a wall brightness of between 15 and
17'000 cd/m2 and this is tolerable for direct viewing over a reasonable time span.
However the current range of T5 (16mm) High Output lamps can have wall
brightness's up to 30'000 cd/m2, these would prove uncomfortable for anything
other than a momentary glance such as when viewed in a circulation space.
Compact lamps can also have extremely high wall brightness's so caution should
be used when specifying lamps. Even then the high brightness lamps should only
be used in luminaires that employ sophisticated optics that prevent or obscure any
direct lamp image.
Luminaire controls can also be used to good effect in limiting the brightness of
luminaires at various times of the day and this will further help with the energy
efficiency of the installation. By regulating or switching off the lamp when
sufficient natural light is available within the room or area great savings can be
made over the life of the installation. The key to the successful use of lighting
controls is to be discriminating about their use, only use controls if a desirable user
benefit or a real energy saving can be determined. In addition the controls should
be simple to operate, understand and use, if they can not be understood by the
staff or patients they will simply not be used and prove in the long term to be an
expensive mistake.
Below: Chromaticity Chart compiled from original information produced
by The Commission Internationale de L'Eclairage (CIE) circa 1931
The above chromaticity chart is based on an attempt to represent colours from the
3 dimensional colour space of human visual perception on to a 2 dimensional graph.
Obviously one of the dimensions can not be represented so colour "intensity" is
omitted showing
only the hue and saturation. The wave lengths in Nanometers
are shown around the chart with each colour being represented by simple X, Y
coordinates. The black body chromaticity locus is shown within the chromaticity
chart together with coordination points for each of the common lamp colour
temperatures shown in degrees Kelvin.
Selecting the correct lamp colour temperature is very important; it should be
chosen to compliment or enhance the selection of surface colours to be used.
Four spectral power curves for different lamp colour temperatures
are shown
below the chart indicating the spectral energy at each of the wave lengths within
the visual spectrum.
