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:

  1. Investigate the Light Pollution in the St Austell area 
  2. Show with photographs and diagrams, how light is scattered from various light fittings. 
  3. 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

 

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