INTRODUCTION

  The Herschel Astronomical Society was established in 1966 to celebrate the work of William Herschel, discoverer of the planet Uranus and so Slough's most celebrated son. Its members are chiefly taken from the Slough, Windsor and Maidenhead area. Some of its members have been actively surveying and recording the night sky for 40 to 60 years and are therefore well placed to describe changes in the visible sky as seen from an urban environment.

1.  What has been the impact of light pollution on UK astronomy?

—  In the 1960's the general limiting magnitude visible with the unaided eye from Langley and Iver in Berkshire was around six. At this time Mercury Vapour lamps were in vogue, and lighting levels at street level were lower than today. On clear evening the Milky Way could be seen by non-astronomers out at night in these suburban areas.

—  By the early 70's, with the introduction of Low Pressure Sodium lighting the situation deteriorated fairly quickly. In the areas mentioned above the limiting magnitude fell below 5.5. The Milky Way was still visible, but the nights had to be particularly clear.

—  By the late 1980's/early 1990's the unaided eye limiting magnitude throughout the Thames Valley has declined to five. Most non-astronomers are now not aware of the Milky Way.

  Typically people walking their dogs in the evenings were aware of the light of the Milky Way in the 60's—but sky glow has all but made it invisible to the casual observer now.

  The introduction of directed High Pressure Sodium lights has not yet improved the general sky glow levels—though they have helped with some localised pollution problems.

  Whilst sky glow is caused by general air pollution illuminated by ground based lights, where there are no lights the situation rapidly improves. For instance, moving from northern Maidenhead to Cookham Dean, approx half a mile away, the limiting magnitude overhead improves by up to 0.5 of a magnitude. This is almost entirely due to the lack of street or building lighting as the distance is too short for there to be much variation in air quality.

2.  Are current planning guidelines strong enough to protect against light pollution?

  Under the Local Plan for Slough it seems that only floodlighting is covered under planning guidelines.

  We would prefer that that security lighting (both for residential and commercial) be included.

3.  Are planning guidelines being applied and enforced effectively?

  Not in a case in Maidenhead during the late 1980's. Developers had installed Low Pressure Sodium lamp standards in a new housing development but the Council ignored this issue and proceeded in adopting the road. After sustained pressure from one of our members, the Council elected to pay for the replacement of the Low Pressure Sodium lamp standards with directed High Pressure ones. We understand the differential cost would have been less than £100 per lamp—if it had been done when the lighting was initially installed.

  Given the small cost penalty, and that the resulting lights are better for both pedestrians and local astronomer's, we suggest it would have been a reasonable policy to only install directed High Pressure Sodium lamps.

4.  Is light measurable in such a way as to make legally enforceable regulatory controls feasible?

  Light is obviously measurable. Just as it is a planning requirement for roads and public places to be lit to an appropriate level it is not unreasonable to legislate what these light levels should be.

  Lighting, like noise, is not restricted to its target audience, but intrudes beyond. We would like to see a control on intrusive light levels so that those who would prefer not to suffer light pollution have some recourse. If only the areas that need to be lit actually receive light then the general level of light pollution will be substantially reduced.

  With some standard in place it would also be possible to determine what level of household lighting is reasonable, with the object of establishing whether floodlights/security lights can be viewed as intrusive to neighbours through their intensity, type or positioning.

5.  Are further controls on the design of lighting necessary?

  In the 1960's many street lights were timed to switch off at midnight or 1am. A return to this policy (at least in side streets, where there is little traffic during these hours) would save electricity and be better for the environment as well as reducing unwanted light.

  Today's electronics would allow for a cheap mechanism to sense dusk and dawn, as at present, but also extinguish the lights between the times suggested. This measure would improve the night skies significantly for astronomers in suburban areas.

  The major costs of street lighting changes like this are in the labour involved in visiting each lamp. Replacing units as and when bulbs fail ought to reduce the cost of making the change.

6.  Summary of Recommendations for Action

  (a)  Local planning guidelines to include street lighting, advertising and security lighting (both public and domestic) as well as floodlighting.

  (b)  Such guidelines to limit the light straying into unintended areas as well as specifying illumination in the target area. Upward directed light is especially damaging.

  (c)  Steps to encourage the switching off of unnecessary light in the overnight period, including both street and commercial lighting.

April 2003