Light Pollution: Chapter One
An article on Light Pollution experiments in and around the St
Austell area, by Tara Hill
The Spread of Light Pollution
Light pollution is all around us though not many people are
aware of it's existence. Britain is one of the worst culprits, it
is ranked third in the light pollution stakes after the USA and
the Netherlands. Since the introduction of street lighting over
100 years ago, light pollution has affected the environment.
Identifying Different Types of Light Pollution
There are three types of light pollution.
- Light Trespass occurs when misdirected light shines
onto a persons property. The light can shine through a persons
bedroom window causing sleepless nights and general
irritation. It can also disrupt a persons enjoyment of their
garden at night not just from an astronomer's point of view
but also from a person who enjoys studying nocturnal species.
- Glare often affects a person traveling in a vehicle,
after driving through an adequately lit area the driver
approaches a security light which shines directly into their
eyes causing their dark adapted eyesight to be blinded by
misdirected light. The worst crime involving glare is security
lighting, it is so bright it actually camouflages anything
going on behind the light, therefore a criminal can go about
his work.
- Skyglow is misdirected light, and this is
best described as the orange glow often seen creeping up into
the night sky, on a cloudy night it will even be apparent when
looking directly above your head.
Skyglow is also an indicator of another type of pollution.
Light likes to travel in straight lines and if the source is
directed straight up the light will pass directly through the
atmosphere without much resistance. However, most light sources
direct light down to the ground which is good, and out to the side
which is bad. The reason it's bad is because the atmosphere is
thicker closer to the ground where there is more water droplets to
travel through and scatter the light. Skyglow is apparent both
close to home and further afield. For example. Friends of mine
live in a dark rural area on the coast near St Austell. Although
they are not astronomers, they enjoy looking at the night sky and
have fitted louvred luminaires in their garden, to reflect the
light downwards. Their main source of light pollution is the
skyglow which is clearly visible over Plymouth, over 20 miles from
their home.
Other Factors Affecting Light Pollution
It is at this point air pollution also has to be considered.
Power plants and vehicles produce sulphate and carbon dioxide
particles, the water droplets cling onto and form around these
particles. When the misdirected light hits the water droplets,
light is scattered, producing the skyglow. It is a sad fact that
the light fittings in general use today produce excessive light
which is misdirected making them inefficient.
Issues to Consider
The night sky is also an educational tool, astronomy is now a
GCSE subject opening up the subject to a lot more enthusiasts. It
also provides important information to scientists, helping us to
understand how our planet formed and what will become of it in the
future. The night sky is full of secrets to be discovered and
therefore should be regarded as a Site of Special Scientific
Interest.
Aims
There are several areas of light pollution that could be
investigated but my main objective will be to discover if and how
much the night sky around the St Austell area has been affected by
street and industrial lighting. I have chosen the night sky
because as an amateur astronomer, the subject is close to heart
and the thought of losing the stars to light pollution would be
unacceptable. St Austell is set in a rural area, which should mean
there are areas where the stars are visible and where the sight in
more populated areas are not. My biggest concern is with the
increasing population and the building of estates, the areas where
observing is possible will become less available as time goes on.
Therefore, the aims of the project are:
- Investigate the Light Pollution in the St Austell area
- Show with photographs and diagrams, how light is scattered
from various light fittings.
- Provide a source of information to educate people on the
basics of light pollution and it's effect of the Astronomer.
Light Fittings and their Effect on Light Pollution
Introduction
Since the introduction of electrically powered street lighting
at the end of the 19th century, the night time environment has
slowly but surely grown brighter and brighter. This is due to
increase in street lighting and the need to light the way and
provide a feeling of security. Over the last decade there has also
been an increase in other types of lighting, such as security and
flood lighting.
Inside the home, people place light shades over their light
bulbs, this directs the light down onto the floor where it is
needed and also reduces the glare from the light bulb, making the
home a warm, relaxing environment. This activity is not always
apparent when lights are designed for outside use.
Street Lighting
Since the 2nd World War, the number of street lights have
slowly increased and in 2000 there were 6.2 million lighting
columns in public ownership (www.ile.co.uk 22.02.02). Many of the
older street lights contribute to the source of light pollution
known as skyglow, the orange tinge that lights up the sky over any
city, town and large village. Some cause light trespass, by
shining light through windows of houses. However, with public
lighting this problem can usually be rectified by contacting the
owner of the light usually the local council, who with reasonable
cause will fit a more modern luminaire, which should reduce the
light trespass into a persons property (www.ile.co.uk 22.02.02).
On average 30% of the light from street lights escapes above
the horizontal, from this figure the Campaign for Dark Skies
estimates £53 million is wasted lighting the sky ( Joy Griffiths
09.01.02). The reason for this waste is the design of the older
style street lighting.
Picture 1
These street lights are most commonly found on busy roads and
areas of high population.
Picture 2
The smaller SCO. luminaires found in villages are serious light
polluters as can be seen in the photo they have been capped but
the lamp is well below the shielding.
Picture 3
These post top luminaires, can be found on most estates,
Aberdeen Close, St Blazey is one example. They may appear to be
sky friendly but a glow of orange is noticeable around them on a
misty night and photo one can show this. Bob Mizon of The Campaign
for Dark Skies, lived on an estate which recently had these lights
replaced with FCO. fittings, he has found the difference
incredible, proving that just replacing a few luminaires is
worthwhile for the immediate locality (Bob Mizon 2001). All the
above light fittings are known as Semi cut off luminaires. This
means they have been capped but the light is not totally shielded.
Therefore if the lamp can be seen underneath the shield, in the
deep glass bowl, a certain amount of light can escape above the
horizontal (Joy Griffiths 09.01.02).
These older fittings are on the approved list of Cornwall
County Council and are used extensively. I have however noticed on
my journeys around the St Austell area that the FCO or Full cut
off designs are being used where new luminaires are installed for
example on the A390 near St Mewan School and the Carluddon
roundabout. In St Austell itself, I have noticed on Trinity Street
and South Street, that the old luminaires have been replaced with
the newer FCO luminaires.
New FCO. Luminaires
Picture 4
Picture 5
(Pictures of all street lights provided by James Lantsbery,
Cornwall County Council 08.02.02)
The Full cut off design luminaires do not produce light
pollution, they are designed to place the light where it is needed
the most. Reflectors and refractors inside the shield will direct
the light towards the ground, the light is concentrated into one
area. This is not only good for reducing light pollution but also
reduces the amount of electricity needed to power the lights. The
reason for this as light is concentrated into a specific area the
full resource of the light is used, a lower wattage bulb can be
used, this reduces electricity and the amount of fossil fuels used
to power them.
Information Obtained from James Lantsbery, Cornwall County
Council. 18.03.02.
The lighting engineers of Cornwall County Council seem to be
well aware of light pollution and take the issue seriously,
especially in rural areas. If they receive complaints they will
act on them and rectify the problem. Like any other organisation
the lighting department at CCC is ruled by a budget, money is
allocated to them at the beginning of the year for the maintenance
and replacement of street lights, however there is no fixed budget
for replacing SCO luminaires with FCO. The replacement of SCO
luminaires will be a gradual process taking place over a number of
years. When the lights are replaced, whole streets will be
refitted at the same time using the original columns, the
luminaires will be constructed to provide the right light for the
column spacing and height. As already mentioned, the limiting
factor is the amount of money available to spend on new fittings,
the older style SCO’s cost the council £100, the newer FCO’s
cost £150.
The conversation with James Lantsbery was very interesting as
it showed that large organisations such as Cornwall County Council
are concerned about light pollution. This could provide a role
model for other institutions to follow suit.
Domestic Security Lighting
Domestic security lights are becoming an increasing problem,
the reason for this is the design of the lights and the lack of
instruction for fitting them. Therefore, many people who are not
aware of light pollution will fit the lamp to the side of their
building, with the fitting directing light out to the horizontal,
as no shielding is placed over the fitting, light will be
scattered in all directions. This not only causes skyglow, but
light trespass and glare.
The average security light bought from the DIY stores is fitted
with a 500 watt bulb, the Institution of Lighting Engineers state
in their guidelines that 150 watts will do the same job quite
adequately if installed correctly with the beam lighting only the
area required. To describe these lights as ‘security’ will
only provide a ‘sense of security’ to the householder, as the
strong light produces deep shadows, perfect cover for a person
intent on causing mischief. Again, as with the street lights using
150 watt instead of the 500 watt bulb will reduce energy costs and
the production of CO2 and SO2 which ultimately ends up polluting
the atmosphere.
The light generated from these fittings will soon become the
main source of light pollution if nothing is done to improve their
design. Although, there are some good designs on the market fitted
with motion sensors and shielding such as the Astrica range, these
tend to be more expensive than the polluting types.
Flood Lighting
Sports grounds such as the football club in St Blazey and
industrial areas such as Imerys, use flood lighting (see diagram
2a). The glow surrounding St Blazey football club on a Wednesday
evening is amazing, it lights up the streets and the side of my
house. Observing the night sky would be impossible when a football
match is on. A Friend who lives in St Merryn, has told me
she can see the lights from Newquay sports club from her house, a
distance of 10 miles. These lights are on every night of the week,
even when the club is not in use.
The china clay industry also uses flood lighting extensively in
the St Austell area. I have driven past many china clay works at
night and they all seem to be lit up with floodlights. Obviously,
safety has to be taken into consideration for this type of
lighting, and it would be wrong for me to suggest they change
their lighting system without proper consultation from a lighting
engineer. However, the use of flood lighting on the entrance to
the Quarry Park Tank Site, next to the Eden project in St Blazey
could be improved. When I visited the site at night, the flood
light was on but the gate was closed suggesting no activity,
therefore the light could not be of any use to works traffic.
Globe Lights
Globe lights can be found in various situations, they are used
on pedestrian crossings and can be quite often seen in car parks.
The unshielded globe lights contribute greatly to light pollution,
they can also produce dark shadows due to their design. The globe
luminaire sits directly on top of the column, therefore the column
acts as a shield and produces a shadow around the base of the
light. The rest of the light is spread around in all directions.
The Par Moor Laboratories car park near St Austell has this type
of lighting (see photo two and diagram 2b), there is no shielding
of any kind on these globe lights. Although they look attractive,
they do nothing for the appreciation of the night sky.
Not all globe lights are bad however. For instance, the
Asda car park on the A390 near St Austell and Aylmer Square in St
Austell has globe lights installed (see photo three and diagram
2c). These lights have shields which cover the top half of the
globe and the bulb is placed up inside the shielding. On closer
inspection, reflectors were also noticed this would redirect the
light where it is most needed.
General Lighting
Other types of lights I have noticed in my survey area which
are polluters are the type that seem to be stuck to the side of a
wall. For example porch lights (see photo four), the owner of the
property could fit shielding to the porch light without too much
trouble and direct more of the light where it is needed. The light
bulb could then be changed to a lower wattage, therefore saving
money.
Other fittings of this type but larger have been seen on the
side of Luxulyan Village Hall and Par Health Centre (see diagram
2d). They give off a surprising amount of light and I am sure
contribute quite a lot to light pollution, as the light is not
shielded, there are several fitted to the buildings and are quite
large luminaires. In my opinion the lights at the Par Health
Centre provide too much light for their intended use as street
lights are plentiful in this area. Luxulyan Village Hall is
probably more justified to have these lights as it is a rural area
with limited street lighting, although they could find a better
design.
Diagram 2d
Diagram 2e
Photographs
|
|
| A Post Top Luminaire with no
shielding. Produces all round light scatter as well as light
tresspass on end of house. |
Unshielded Glode light in Par.
Again all round light scatter is evident. |
|
|
| A well designed Globe light where the lamp is
located within the shielding. Light can only be directed
downwards where it is needed. |
The results of an unshielded
porch light. Notice the light escaping above the horizontal
and onto the side of the house. |
|
|
| Old and New: The lamp on the left
of the picture is the new F.C.O Luminaire, while on the
right is the older S.C.O design. Evidence that there is a
willingness to install the better F.C.O designs. |
Notice miss-directed light
illuminating the tree. Skyglow is very evident towards the
horizontal, but with an increase in elevation, more stars
start to become visible. |
|
|
| This photo shows both the older
S.C.O and partially shielded lamp designs |
A photo of the Aurora Borealis or
Northern Lights. If light pollution is allowed to continue
unchecked, then this is a sight that will become rarer. As
an amateur astronomer, I am obviously biased, but I am sure
I am not the only person who would rather look this than
skyglow. |
Forward to Chapter Two
